diff --git a/README.md b/README.md
index b548d0c..489433b 100644
--- a/README.md
+++ b/README.md
@@ -15,32 +15,33 @@ Regorus is available as a library that can be easily integrated into your Rust p
 
 ## Getting Started
 
-[regorus](examples/regorus.rs) is an example program that shows how to integrate Regorus into your project and evaluate Rego policies.
+[examples/regorus](examples/regorus.rs) is an example program that shows how to integrate Regorus into your project and evaluate Rego policies.
 
-To build it, do
+To build and install it, do
 
-    cargo build -r --example regorus
+    cargo install --example regorus --path .
 
 
 Check that the regorus example program is working
 
-    $ target/release/examples/regorus
+    $ regorus
     Usage: regorus <COMMAND>
     
     Commands:
       eval   Evaluate a Rego Query
       lex    Tokenize a Rego policy
-      parse  Parse q Rego policy
+      parse  Parse a Rego policy
       help   Print this message or the help of the given subcommand(s)
-
+    
     Options:
       -h, --help     Print help
-      -V, --version  Print version
+      -V, --version  Print versionUsage: regorus <COMMAND>
+
 
 
 First, let's evaluate a simple Rego expression `1*2+3`
 
-    target/release/examples/regorus eval "1*2+3"
+    regorus eval "1*2+3"
 
 This produces the following output
 
@@ -63,16 +64,11 @@ This produces the following output
 
 Next, evaluate a sample [policy](examples/example.rego) and [input](examples/input.json) (borrowed from [Rego tutorial](https://www.openpolicyagent.org/docs/latest/#2-try-opa-eval)):
 
-    target/release/examples/regorus eval -d examples/example.rego -i examples/input.json data.example
+    regorus eval -d examples/example.rego -i examples/input.json data.example
 
 Finally, evaluate real-world [policies](tests/aci/) used in Azure Container Instances (ACI)
 
-    target/release/examples/regorus eval -d tests/aci/framework.rego \
-        -d tests/aci/policy.rego \
-        -d tests/aci/api.rego  \
-        -d tests/aci/data.json  \
-        -i tests/aci/input.json \
-         data.policy.mount_overlay=x
+    regorus eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.policy.mount_overlay=x
 
 
 ## ACI Policies
@@ -94,26 +90,24 @@ Regorus successfully passes the ACI policy test-suite. It is fast and can run ea
 
 Run the ACI policies in the `tests/aci` directory, using data `tests/aci/data.json` and input `tests/aci/input.json`:
 
-    target/release/examples/regorus eval \
-         -b tests/aci \
-         -d tests/aci/data.json \
-         -i tests/aci/input.json \
-         data.framework.mount_overlay=x
+    regorus eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.policy.mount_overlay=x
+
 
 Verify that [OPA](https://github.com/open-policy-agent/opa/releases) produces the same output
 
-    diff <(target/release/examples/regorus eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x) <(opa eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x)
+    diff <(regorus eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x) \
+         <(opa eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x)
 
 ## Performance
 
 To check how fast Regorus runs on your system, first install a tool like [hyperfine](https://github.com/sharkdp/hyperfine).
 
-   cargo install hyperfine
+    cargo install hyperfine
 
 Then benchmark evaluation of the ACI policies,
 
-    $ hyperfine "target/release/examples/regorus eval -b tests/aci -d tests/aci/data.json -i   tests/aci/input.json data.framework.mount_overlay=x"
-    Benchmark 1: target/release/examples/regorus eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x
+    $ hyperfine "regorus eval -b tests/aci -d tests/aci/data.json -i   tests/aci/input.json data.framework.mount_overlay=x"
+    Benchmark 1: regorus eval -b tests/aci -d tests/aci/data.json -i tests/aci/input.json data.framework.mount_overlay=x
       Time (mean ± σ):       4.6 ms ±   0.2 ms    [User: 4.1 ms, System: 0.4 ms]
       Range (min … max):     4.4 ms …   6.0 ms    422 runs
  
diff --git a/examples/regorus.rs b/examples/regorus.rs
index 1bdb296..8cc2d69 100644
--- a/examples/regorus.rs
+++ b/examples/regorus.rs
@@ -142,7 +142,7 @@ enum RegorusCommand {
         verbose: bool,
     },
 
-    /// Parse q Rego policy.
+    /// Parse a Rego policy.
     Parse {
         /// Rego policy file.
         file: String,
diff --git a/src/ast.rs b/src/ast.rs
index a66dfea..3eb3975 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -321,6 +321,7 @@ pub enum Rule {
     Default {
         span: Span,
         refr: Ref<Expr>,
+        args: Vec<Ref<Expr>>,
         op: AssignOp,
         value: Ref<Expr>,
     },
diff --git a/src/builtins/aggregates.rs b/src/builtins/aggregates.rs
index f7e4025..0d6c226 100644
--- a/src/builtins/aggregates.rs
+++ b/src/builtins/aggregates.rs
@@ -21,7 +21,7 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("sum", (sum, 1));
 }
 
-fn count(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn count(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "count", params, args, 1)?;
 
     Ok(Value::from(Number::from(match &args[0] {
@@ -38,7 +38,7 @@ fn count(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })))
 }
 
-fn max(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn max(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "max", params, args, 1)?;
 
     Ok(match &args[0] {
@@ -53,7 +53,7 @@ fn max(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })
 }
 
-fn min(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn min(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "min", params, args, 1)?;
 
     Ok(match &args[0] {
@@ -68,7 +68,7 @@ fn min(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })
 }
 
-fn product(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn product(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "product", params, args, 1)?;
 
     let mut v = Number::from(1_u64);
@@ -93,7 +93,7 @@ fn product(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     }))
 }
 
-fn sort(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn sort(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "sort", params, args, 1)?;
     Ok(match &args[0] {
         Value::Array(a) => {
@@ -110,7 +110,7 @@ fn sort(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })
 }
 
-fn sum(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn sum(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "sum", params, args, 1)?;
 
     let mut v = Number::from(0_u64);
diff --git a/src/builtins/arrays.rs b/src/builtins/arrays.rs
index fe5c04d..1375787 100644
--- a/src/builtins/arrays.rs
+++ b/src/builtins/arrays.rs
@@ -18,7 +18,7 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("array.slice", (slice, 3));
 }
 
-fn concat(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn concat(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "array.concat";
     ensure_args_count(span, name, params, args, 2)?;
     let mut v1 = ensure_array(name, &params[0], args[0].clone())?;
@@ -28,7 +28,7 @@ fn concat(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     Ok(Value::Array(v1))
 }
 
-fn reverse(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn reverse(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "array.reverse";
     ensure_args_count(span, name, params, args, 1)?;
 
@@ -37,7 +37,7 @@ fn reverse(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     Ok(Value::Array(v1))
 }
 
-fn slice(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn slice(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "array.slice";
     ensure_args_count(span, name, params, args, 3)?;
 
diff --git a/src/builtins/bitwise.rs b/src/builtins/bitwise.rs
index 82e035e..deac304 100644
--- a/src/builtins/bitwise.rs
+++ b/src/builtins/bitwise.rs
@@ -21,7 +21,7 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("bits.xor", (xor, 2));
 }
 
-fn and(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn and(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "bits.and";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -34,7 +34,7 @@ fn and(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })
 }
 
-fn lsh(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn lsh(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "bits.lsh";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -47,7 +47,7 @@ fn lsh(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })
 }
 
-fn negate(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn negate(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "bits.negate";
     ensure_args_count(span, name, params, args, 1)?;
 
@@ -59,7 +59,7 @@ fn negate(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })
 }
 
-fn or(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn or(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "bits.or";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -72,7 +72,7 @@ fn or(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })
 }
 
-fn rsh(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn rsh(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "bits.rsh";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -85,7 +85,7 @@ fn rsh(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })
 }
 
-fn xor(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn xor(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "bits.xor";
     ensure_args_count(span, name, params, args, 2)?;
 
diff --git a/src/builtins/conversions.rs b/src/builtins/conversions.rs
index c7d4631..afb35fd 100644
--- a/src/builtins/conversions.rs
+++ b/src/builtins/conversions.rs
@@ -15,12 +15,13 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("to_number", (to_number, 1));
 }
 
-fn to_number(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn to_number(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "to_number";
     ensure_args_count(span, name, params, args, 1)?;
 
     let span = params[0].span();
     Ok(match &args[0] {
+        Value::Null => Value::from(0u64),
         Value::Bool(true) => Value::from(1u64),
         Value::Bool(false) => Value::from(0u64),
         Value::Number(_) => args[0].clone(),
@@ -34,7 +35,9 @@ fn to_number(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value>
             }
         },
         _ => {
-            bail!(span.error(format!("`{name}` expects bool/number/string argument.").as_str()));
+            bail!(
+                span.error(format!("`{name}` expects bool/number/string/null argument.").as_str())
+            );
         }
     })
 }
diff --git a/src/builtins/crypto.rs b/src/builtins/crypto.rs
index e377b70..a0aa071 100644
--- a/src/builtins/crypto.rs
+++ b/src/builtins/crypto.rs
@@ -28,7 +28,12 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("crypto.sha256", (crypto_sha256, 1));
 }
 
-fn hmac_equal_fixed_time(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn hmac_equal_fixed_time(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "crypto.hmac.equal";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -41,7 +46,7 @@ fn hmac_equal_fixed_time(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> R
     )))
 }
 
-fn hmac_md5(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn hmac_md5(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "crypto.hmac.md5";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -57,7 +62,7 @@ fn hmac_md5(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value>
     Ok(Value::String(hex::encode(result.into_bytes()).into()))
 }
 
-fn hmac_sha1(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn hmac_sha1(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "crypto.hmac.sha1";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -73,7 +78,7 @@ fn hmac_sha1(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value>
     Ok(Value::String(hex::encode(result.into_bytes()).into()))
 }
 
-fn hmac_sha256(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn hmac_sha256(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "crypto.hmac.sha256";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -89,7 +94,7 @@ fn hmac_sha256(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Valu
     Ok(Value::String(hex::encode(result.into_bytes()).into()))
 }
 
-fn hmac_sha512(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn hmac_sha512(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "crypto.hmac.sha512";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -105,7 +110,7 @@ fn hmac_sha512(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Valu
     Ok(Value::String(hex::encode(result.into_bytes()).into()))
 }
 
-fn crypto_md5(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn crypto_md5(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "crypto.md5";
     ensure_args_count(span, name, params, args, 1)?;
 
@@ -119,7 +124,7 @@ fn crypto_md5(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value
     Ok(Value::String(hex::encode(result).into()))
 }
 
-fn crypto_sha1(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn crypto_sha1(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "crypto.sha1";
     ensure_args_count(span, name, params, args, 1)?;
 
@@ -133,7 +138,12 @@ fn crypto_sha1(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Valu
     Ok(Value::String(hex::encode(result).into()))
 }
 
-fn crypto_sha256(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn crypto_sha256(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "crypto.sha256";
     ensure_args_count(span, name, params, args, 1)?;
 
diff --git a/src/builtins/debugging.rs b/src/builtins/debugging.rs
index 0c0a582..bb77b14 100644
--- a/src/builtins/debugging.rs
+++ b/src/builtins/debugging.rs
@@ -20,7 +20,7 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
 // Symbol analyzer must ensure that vars used by print are defined before
 // the print statement. Scheduler must ensure the above constraint.
 // Additionally interpreter must allow undefined inputs to print.
-fn print(span: &Span, _params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn print(span: &Span, _params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     if args.len() > MAX_ARGS as usize {
         bail!(span.error("print supports up to 100 arguments"));
     }
diff --git a/src/builtins/deprecated.rs b/src/builtins/deprecated.rs
index e3bc5df..6e7d6af 100644
--- a/src/builtins/deprecated.rs
+++ b/src/builtins/deprecated.rs
@@ -19,7 +19,13 @@ lazy_static! {
 	let mut m : HashMap<&'static str, BuiltinFcn>  = HashMap::new();
 	
 	m.insert("all", (all, 1));
-	m.insert("any", (any, 1));	
+	m.insert("any", (any, 1));
+	m.insert("cast_array", (cast_array, 1));
+	m.insert("cast_boolean", (cast_boolean, 1));
+	m.insert("cast_null", (cast_null, 1));
+	m.insert("cast_object", (cast_object, 1));
+	m.insert("cast_set", (cast_set, 1));
+	m.insert("cast_string", (cast_string, 1));
 	m.insert("set_diff", (set_diff, 2));
 
 	#[cfg(feature = "crypto")]
@@ -28,7 +34,7 @@ lazy_static! {
     };
 }
 
-fn all(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn all(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "all", params, args, 1)?;
 
     Ok(Value::Bool(match &args[0] {
@@ -41,7 +47,7 @@ fn all(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     }))
 }
 
-fn any(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn any(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "any", params, args, 1)?;
 
     Ok(Value::Bool(match &args[0] {
@@ -54,10 +60,70 @@ fn any(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     }))
 }
 
-fn set_diff(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn set_diff(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "set_diff";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_set(name, &params[0], args[0].clone())?;
     let s2 = ensure_set(name, &params[1], args[1].clone())?;
     Ok(Value::from_set(s1.difference(&s2).cloned().collect()))
 }
+
+fn cast_array(span: &Span, params: &[Ref<Expr>], args: &[Value], strict: bool) -> Result<Value> {
+    let name = "cast_array";
+    ensure_args_count(span, name, params, args, 1)?;
+    match &args[0] {
+        Value::Array(_) => Ok(args[0].clone()),
+        _ if strict => bail!(params[0].span().error("array required")),
+        _ => Ok(Value::Undefined),
+    }
+}
+
+fn cast_boolean(span: &Span, params: &[Ref<Expr>], args: &[Value], strict: bool) -> Result<Value> {
+    let name = "cast_boolean";
+    ensure_args_count(span, name, params, args, 1)?;
+    match &args[0] {
+        Value::Bool(_) => Ok(args[0].clone()),
+        _ if strict => bail!(params[0].span().error("boolean required")),
+        _ => Ok(Value::Undefined),
+    }
+}
+
+fn cast_null(span: &Span, params: &[Ref<Expr>], args: &[Value], strict: bool) -> Result<Value> {
+    let name = "cast_null";
+    ensure_args_count(span, name, params, args, 1)?;
+    match &args[0] {
+        Value::Null => Ok(Value::Null),
+        _ if strict => bail!(params[0].span().error("null required")),
+        _ => Ok(Value::Undefined),
+    }
+}
+
+fn cast_object(span: &Span, params: &[Ref<Expr>], args: &[Value], strict: bool) -> Result<Value> {
+    let name = "cast_object";
+    ensure_args_count(span, name, params, args, 1)?;
+    match &args[0] {
+        Value::Object(_) => Ok(args[0].clone()),
+        _ if strict => bail!(params[0].span().error("object required")),
+        _ => Ok(Value::Undefined),
+    }
+}
+
+fn cast_set(span: &Span, params: &[Ref<Expr>], args: &[Value], strict: bool) -> Result<Value> {
+    let name = "cast_set";
+    ensure_args_count(span, name, params, args, 1)?;
+    match &args[0] {
+        Value::Set(_) => Ok(args[0].clone()),
+        _ if strict => bail!(params[0].span().error("set required")),
+        _ => Ok(Value::Undefined),
+    }
+}
+
+fn cast_string(span: &Span, params: &[Ref<Expr>], args: &[Value], strict: bool) -> Result<Value> {
+    let name = "cast_string";
+    ensure_args_count(span, name, params, args, 1)?;
+    match &args[0] {
+        Value::String(_) => Ok(args[0].clone()),
+        _ if strict => bail!(params[0].span().error("string required")),
+        _ => Ok(Value::Undefined),
+    }
+}
diff --git a/src/builtins/encoding.rs b/src/builtins/encoding.rs
index 108ff84..7df87b8 100644
--- a/src/builtins/encoding.rs
+++ b/src/builtins/encoding.rs
@@ -26,7 +26,12 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     }
 }
 
-fn base64_decode(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn base64_decode(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "base64.decode";
     ensure_args_count(span, name, params, args, 1)?;
 
@@ -38,7 +43,12 @@ fn base64_decode(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Va
 }
 
 #[cfg(feature = "yaml")]
-fn yaml_is_valid(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn yaml_is_valid(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "yaml.is_valid";
     ensure_args_count(span, name, params, args, 1)?;
 
@@ -47,7 +57,7 @@ fn yaml_is_valid(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Va
 }
 
 #[cfg(feature = "yaml")]
-fn yaml_marshal(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn yaml_marshal(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "yaml.marshal";
     ensure_args_count(span, name, params, args, 1)?;
     Ok(Value::String(
@@ -58,14 +68,24 @@ fn yaml_marshal(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Val
 }
 
 #[cfg(feature = "yaml")]
-fn yaml_unmarshal(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn yaml_unmarshal(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "yaml.unmarshal";
     ensure_args_count(span, name, params, args, 1)?;
     let yaml_str = ensure_string(name, &params[0], &args[0])?;
     Value::from_yaml_str(&yaml_str).with_context(|| span.error("could not deserialize yaml."))
 }
 
-fn json_is_valid(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn json_is_valid(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "json.is_valid";
     ensure_args_count(span, name, params, args, 1)?;
 
@@ -73,7 +93,7 @@ fn json_is_valid(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Va
     Ok(Value::Bool(Value::from_json_str(&json_str).is_ok()))
 }
 
-fn json_marshal(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn json_marshal(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "json.marshal";
     ensure_args_count(span, name, params, args, 1)?;
     Ok(Value::String(
@@ -83,7 +103,12 @@ fn json_marshal(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Val
     ))
 }
 
-fn json_unmarshal(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn json_unmarshal(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "json.unmarshal";
     ensure_args_count(span, name, params, args, 1)?;
     let json_str = ensure_string(name, &params[0], &args[0])?;
diff --git a/src/builtins/glob.rs b/src/builtins/glob.rs
index b55b2a3..b3993b1 100644
--- a/src/builtins/glob.rs
+++ b/src/builtins/glob.rs
@@ -55,7 +55,7 @@ fn make_glob<'a>(pattern: &'a str, span: &'a Span) -> Result<Glob<'a>> {
     Glob::new(pattern).or_else(|_| bail!(span.error("invalid glob")))
 }
 
-fn glob_match(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn glob_match(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "glob.match";
     ensure_args_count(span, name, params, args, 3)?;
 
@@ -101,7 +101,7 @@ fn glob_match(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value
     Ok(Value::Bool(glob.is_match(&value[..])))
 }
 
-fn quote_meta(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn quote_meta(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "glob.quote_meta";
     ensure_args_count(span, name, params, args, 1)?;
 
diff --git a/src/builtins/mod.rs b/src/builtins/mod.rs
index 714cfcc..af6391c 100644
--- a/src/builtins/mod.rs
+++ b/src/builtins/mod.rs
@@ -38,7 +38,7 @@ use std::collections::HashMap;
 use anyhow::Result;
 use lazy_static::lazy_static;
 
-pub type BuiltinFcn = (fn(&Span, &[Ref<Expr>], &[Value]) -> Result<Value>, u8);
+pub type BuiltinFcn = (fn(&Span, &[Ref<Expr>], &[Value], bool) -> Result<Value>, u8);
 
 #[cfg(feature = "deprecated")]
 pub use deprecated::DEPRECATED;
diff --git a/src/builtins/numbers.rs b/src/builtins/numbers.rs
index 7238b2d..bc2428e 100644
--- a/src/builtins/numbers.rs
+++ b/src/builtins/numbers.rs
@@ -48,28 +48,28 @@ pub fn arithmetic_operation(
     }))
 }
 
-fn abs(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn abs(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "abs", params, args, 1)?;
     Ok(Value::from(
         ensure_numeric("abs", &params[0], &args[0])?.abs(),
     ))
 }
 
-fn ceil(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn ceil(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "ceil", params, args, 1)?;
     Ok(Value::from(
         ensure_numeric("ceil", &params[0], &args[0])?.ceil(),
     ))
 }
 
-fn floor(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn floor(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "floor", params, args, 1)?;
     Ok(Value::from(
         ensure_numeric("floor", &params[0], &args[0])?.floor(),
     ))
 }
 
-fn range(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn range(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "numbers.range", params, args, 2)?;
     let v1 = ensure_numeric("numbers.range", &params[0], &args[0].clone())?;
     let v2 = ensure_numeric("numbers.range", &params[1], &args[1].clone())?;
@@ -96,14 +96,14 @@ fn range(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     Ok(Value::from_array(values))
 }
 
-fn round(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn round(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "round", params, args, 1)?;
     Ok(Value::from(
         ensure_numeric("round", &params[0], &args[0])?.round(),
     ))
 }
 
-fn intn(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn intn(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let fcn = "rand.intn";
     ensure_args_count(span, fcn, params, args, 2)?;
     let _ = ensure_string(fcn, &params[0], &args[0])?;
diff --git a/src/builtins/objects.rs b/src/builtins/objects.rs
index 97ffa84..7f23a52 100644
--- a/src/builtins/objects.rs
+++ b/src/builtins/objects.rs
@@ -122,7 +122,7 @@ fn merge_filters(
     Ok(filters)
 }
 
-fn json_filter(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn json_filter(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "json.filter";
     ensure_args_count(span, name, params, args, 2)?;
     ensure_object(name, &params[0], args[0].clone())?;
@@ -136,7 +136,7 @@ fn json_filter(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Valu
     Ok(json_filter_impl(&args[0], &filters))
 }
 
-fn filter(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn filter(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "object.filter";
     ensure_args_count(span, name, params, args, 2)?;
     let mut obj = ensure_object(name, &params[0], args[0].clone())?;
@@ -154,7 +154,7 @@ fn filter(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     Ok(Value::Object(obj))
 }
 
-fn get(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn get(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "object.get";
     ensure_args_count(span, name, params, args, 3)?;
     let obj = ensure_object(name, &params[0], args[0].clone())?;
@@ -179,14 +179,14 @@ fn get(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     })
 }
 
-fn keys(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn keys(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "object.keys";
     ensure_args_count(span, name, params, args, 1)?;
     let obj = ensure_object(name, &params[0], args[0].clone())?;
     Ok(Value::from_set(obj.keys().cloned().collect()))
 }
 
-fn remove(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn remove(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "object.remove";
     ensure_args_count(span, name, params, args, 2)?;
     let mut obj = ensure_object(name, &params[0], args[0].clone())?;
@@ -225,7 +225,7 @@ fn is_subset(sup: &Value, sub: &Value) -> bool {
     }
 }
 
-fn subset(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn subset(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "object.subset";
     ensure_args_count(span, name, params, args, 2)?;
 
diff --git a/src/builtins/regex.rs b/src/builtins/regex.rs
index 6e5de98..6b80b14 100644
--- a/src/builtins/regex.rs
+++ b/src/builtins/regex.rs
@@ -26,7 +26,12 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("regex.template_match", (regex_template_match, 4));
 }
 
-fn find_all_string_submatch_n(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn find_all_string_submatch_n(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "regex.find_all_string_submatch_n";
     ensure_args_count(span, name, params, args, 3)?;
 
@@ -68,7 +73,7 @@ fn find_all_string_submatch_n(span: &Span, params: &[Ref<Expr>], args: &[Value])
     ))
 }
 
-fn find_n(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn find_n(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "regex.find_n";
     ensure_args_count(span, name, params, args, 3)?;
 
@@ -98,14 +103,19 @@ fn find_n(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     ))
 }
 
-fn is_valid(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn is_valid(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "regex.is_valid";
     ensure_args_count(span, name, params, args, 1)?;
     Ok(ensure_string(name, &params[0], &args[0])
         .map_or(Value::Bool(false), |p| Value::Bool(Regex::new(&p).is_ok())))
 }
 
-pub fn regex_match(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+pub fn regex_match(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "regex.match";
     ensure_args_count(span, name, params, args, 2)?;
     let pattern = ensure_string(name, &params[0], &args[0])?;
@@ -116,7 +126,12 @@ pub fn regex_match(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<
     Ok(Value::Bool(pattern.is_match(&value)))
 }
 
-fn regex_replace(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn regex_replace(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "regex.replace";
     ensure_args_count(span, name, params, args, 3)?;
 
@@ -135,7 +150,7 @@ fn regex_replace(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Va
     ))
 }
 
-fn regex_split(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn regex_split(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "regex.split";
     ensure_args_count(span, name, params, args, 2)?;
     let pattern = ensure_string(name, &params[0], &args[0])?;
@@ -151,7 +166,12 @@ fn regex_split(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Valu
     ))
 }
 
-fn regex_template_match(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn regex_template_match(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "regex.template_match";
     ensure_args_count(span, name, params, args, 4)?;
     let template = ensure_string(name, &params[0], &args[0])?;
diff --git a/src/builtins/semver.rs b/src/builtins/semver.rs
index 7748587..b34a863 100644
--- a/src/builtins/semver.rs
+++ b/src/builtins/semver.rs
@@ -19,7 +19,7 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("semver.is_valid", (is_valid, 1));
 }
 
-fn compare(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn compare(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "semver.compare";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -35,7 +35,7 @@ fn compare(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     Ok(Value::from(result as i64))
 }
 
-fn is_valid(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn is_valid(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "semver.is_valid";
     ensure_args_count(span, name, params, args, 1)?;
     let v = ensure_string(name, &params[0], &args[0])?;
diff --git a/src/builtins/sets.rs b/src/builtins/sets.rs
index 8eca717..e4c0f78 100644
--- a/src/builtins/sets.rs
+++ b/src/builtins/sets.rs
@@ -34,7 +34,12 @@ pub fn difference(expr1: &Expr, expr2: &Expr, v1: Value, v2: Value) -> Result<Va
     Ok(Value::from_set(s1.difference(&s2).cloned().collect()))
 }
 
-fn intersection_of_set_of_sets(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn intersection_of_set_of_sets(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "intersection";
     ensure_args_count(span, name, params, args, 1)?;
     let set = ensure_set(name, &params[0], args[0].clone())?;
@@ -61,7 +66,12 @@ fn intersection_of_set_of_sets(span: &Span, params: &[Ref<Expr>], args: &[Value]
     Ok(Value::from_set(res))
 }
 
-fn union_of_set_of_sets(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn union_of_set_of_sets(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "union";
     ensure_args_count(span, name, params, args, 1)?;
     let set = ensure_set(name, &params[0], args[0].clone())?;
diff --git a/src/builtins/strings.rs b/src/builtins/strings.rs
index 53b3d98..1835ec2 100644
--- a/src/builtins/strings.rs
+++ b/src/builtins/strings.rs
@@ -42,7 +42,7 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("upper", (upper, 1));
 }
 
-fn concat(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn concat(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "concat";
     ensure_args_count(span, name, params, args, 2)?;
     let delimiter = ensure_string(name, &params[0], &args[0])?;
@@ -50,7 +50,7 @@ fn concat(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     Ok(Value::String(collection.join(&delimiter).into()))
 }
 
-fn contains(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn contains(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "contains";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -58,7 +58,7 @@ fn contains(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value>
     Ok(Value::Bool(s1.contains(s2.as_ref())))
 }
 
-fn endswith(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn endswith(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "endswith";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -76,7 +76,7 @@ fn format_number(n: &Number, base: u64) -> String {
     }
 }
 
-fn format_int(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn format_int(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "format_int";
     ensure_args_count(span, name, params, args, 2)?;
     let mut n = ensure_numeric(name, &params[0], &args[0])?;
@@ -97,7 +97,7 @@ fn format_int(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value
     ))
 }
 
-fn indexof(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn indexof(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "indexof";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -109,7 +109,7 @@ fn indexof(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
 }
 
 #[allow(dead_code)]
-fn indexof_n(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn indexof_n(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "indexof_n";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -128,14 +128,14 @@ fn indexof_n(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value>
     Ok(Value::from_array(positions))
 }
 
-fn lower(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn lower(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "lower";
     ensure_args_count(span, name, params, args, 1)?;
     let s = ensure_string(name, &params[0], &args[0])?;
     Ok(Value::String(s.to_lowercase().into()))
 }
 
-fn replace(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn replace(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "replace";
     ensure_args_count(span, name, params, args, 3)?;
     let s = ensure_string(name, &params[0], &args[0])?;
@@ -144,7 +144,7 @@ fn replace(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     Ok(Value::String(s.replace(old.as_ref(), new.as_ref()).into()))
 }
 
-fn split(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn split(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "replace";
     ensure_args_count(span, name, params, args, 2)?;
     let s = ensure_string(name, &params[0], &args[0])?;
@@ -157,7 +157,7 @@ fn split(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     ))
 }
 
-fn sprintf(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn sprintf(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "sprintf";
     ensure_args_count(span, name, params, args, 2)?;
     let fmt = ensure_string(name, &params[0], &args[0])?;
@@ -345,7 +345,12 @@ fn sprintf(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     Ok(Value::String(s.into()))
 }
 
-fn any_prefix_match(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn any_prefix_match(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "strings.any_prefix_match";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -376,7 +381,12 @@ fn any_prefix_match(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result
     ))
 }
 
-fn any_suffix_match(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn any_suffix_match(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     let name = "strings.any_suffix_match";
     ensure_args_count(span, name, params, args, 2)?;
 
@@ -407,7 +417,7 @@ fn any_suffix_match(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result
     ))
 }
 
-fn startswith(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn startswith(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "startswith";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -415,7 +425,7 @@ fn startswith(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value
     Ok(Value::Bool(s1.starts_with(s2.as_ref())))
 }
 
-fn replace_n(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn replace_n(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "trim";
     ensure_args_count(span, name, params, args, 2)?;
     let obj = ensure_object(name, &params[0], args[0].clone())?;
@@ -438,14 +448,14 @@ fn replace_n(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value>
     Ok(Value::String(s.clone()))
 }
 
-fn reverse(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn reverse(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "reverse";
     ensure_args_count(span, name, params, args, 1)?;
     let s = ensure_string(name, &params[0], &args[0])?;
     Ok(Value::String(s.chars().rev().collect::<String>().into()))
 }
 
-fn substring(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn substring(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "substring";
     ensure_args_count(span, name, params, args, 3)?;
     let s = ensure_string(name, &params[0], &args[0])?;
@@ -470,7 +480,7 @@ fn substring(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value>
     }
 }
 
-fn trim(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn trim(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "trim";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -478,7 +488,7 @@ fn trim(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
     Ok(Value::String(s1.trim_matches(|c| s2.contains(c)).into()))
 }
 
-fn trim_left(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn trim_left(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "trim_left";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -488,7 +498,7 @@ fn trim_left(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value>
     ))
 }
 
-fn trim_prefix(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn trim_prefix(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "trim_prefix";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -499,7 +509,7 @@ fn trim_prefix(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Valu
     }))
 }
 
-fn trim_right(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn trim_right(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "trim_right";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -509,14 +519,14 @@ fn trim_right(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value
     ))
 }
 
-fn trim_space(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn trim_space(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "trim_space";
     ensure_args_count(span, name, params, args, 1)?;
     let s = ensure_string(name, &params[0], &args[0])?;
     Ok(Value::String(s.trim().into()))
 }
 
-fn trim_suffix(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn trim_suffix(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "trim_suffix";
     ensure_args_count(span, name, params, args, 2)?;
     let s1 = ensure_string(name, &params[0], &args[0])?;
@@ -527,7 +537,7 @@ fn trim_suffix(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Valu
     }))
 }
 
-fn upper(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn upper(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "upper";
     ensure_args_count(span, name, params, args, 1)?;
     let s = ensure_string(name, &params[0], &args[0])?;
diff --git a/src/builtins/time.rs b/src/builtins/time.rs
index 2b692fe..0291160 100644
--- a/src/builtins/time.rs
+++ b/src/builtins/time.rs
@@ -16,7 +16,7 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("time.now_ns", (now_ns, 0));
 }
 
-fn now_ns(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn now_ns(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "time.now_ns";
     ensure_args_count(span, name, params, args, 0)?;
 
diff --git a/src/builtins/tracing.rs b/src/builtins/tracing.rs
index 9a8dc3b..2870107 100644
--- a/src/builtins/tracing.rs
+++ b/src/builtins/tracing.rs
@@ -17,7 +17,7 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
 
 // Symbol analyzer must ensure that vars used by trace are defined before
 // the trace statement. Scheduler must ensure the above constraint.
-fn trace(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn trace(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "trace";
     ensure_args_count(span, name, params, args, 1)?;
     let msg = ensure_string(name, &params[0], &args[0])?;
diff --git a/src/builtins/types.rs b/src/builtins/types.rs
index b58bb6a..bc11b0e 100644
--- a/src/builtins/types.rs
+++ b/src/builtins/types.rs
@@ -22,37 +22,37 @@ pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("type_name", (type_name, 1));
 }
 
-fn is_array(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn is_array(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "is_array", params, args, 1)?;
     Ok(Value::Bool(matches!(&args[0], Value::Array(_))))
 }
 
-fn is_boolean(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn is_boolean(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "is_boolean", params, args, 1)?;
     Ok(Value::Bool(matches!(&args[0], Value::Bool(_))))
 }
 
-fn is_null(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn is_null(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "is_null", params, args, 1)?;
     Ok(Value::Bool(matches!(&args[0], Value::Null)))
 }
 
-fn is_number(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn is_number(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "is_number", params, args, 1)?;
     Ok(Value::Bool(matches!(&args[0], Value::Number(_))))
 }
 
-fn is_object(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn is_object(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "is_object", params, args, 1)?;
     Ok(Value::Bool(matches!(&args[0], Value::Object(_))))
 }
 
-fn is_set(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn is_set(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "is_set", params, args, 1)?;
     Ok(Value::Bool(matches!(&args[0], Value::Set(_))))
 }
 
-fn is_string(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn is_string(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     ensure_args_count(span, "is_string", params, args, 1)?;
     Ok(Value::Bool(matches!(&args[0], Value::String(_))))
 }
@@ -70,7 +70,12 @@ pub fn get_type(value: &Value) -> &str {
     }
 }
 
-pub fn type_name(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+pub fn type_name(
+    span: &Span,
+    params: &[Ref<Expr>],
+    args: &[Value],
+    _strict: bool,
+) -> Result<Value> {
     ensure_args_count(span, "type_name", params, args, 1)?;
     Ok(Value::String(get_type(&args[0]).into()))
 }
diff --git a/src/builtins/units.rs b/src/builtins/units.rs
index df67d1d..6598c65 100644
--- a/src/builtins/units.rs
+++ b/src/builtins/units.rs
@@ -66,7 +66,7 @@ fn two_exp(suffix: &str) -> Option<i32> {
     })
 }
 
-fn parse(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn parse(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
     let name = "units.parse";
     ensure_args_count(span, name, params, args, 1)?;
     let string = ensure_string(name, &params[0], &args[0])?;
@@ -143,7 +143,7 @@ fn tenb_exp(suffix: &str) -> Option<i32> {
     })
 }
 
-fn parse_bytes(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Value> {
+fn parse_bytes(span: &Span, params: &[Ref<Expr>], args: &[Value], strict: bool) -> Result<Value> {
     let name = "units.parse_bytes";
     ensure_args_count(span, name, params, args, 1)?;
     let string = ensure_string(name, &params[0], &args[0])?;
@@ -166,12 +166,15 @@ fn parse_bytes(span: &Span, params: &[Ref<Expr>], args: &[Value]) -> Result<Valu
         _ => (string, ""),
     };
 
-    let v: Value = if number_part.starts_with('.') {
+    let v: Value = match if number_part.starts_with('.') {
         serde_json::from_str(format!("0{number_part}").as_str())
     } else {
         serde_json::from_str(number_part)
-    }
-    .with_context(|| span.error("could not parse number"))?;
+    } {
+        Ok(v) => v,
+        Err(_) if strict => bail!(span.error("could not parse number")),
+        _ => return Ok(Value::Undefined),
+    };
 
     let mut n = match v {
         Value::Number(n) => n.clone(),
diff --git a/src/engine.rs b/src/engine.rs
index 8cb61f2..10a826e 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -71,6 +71,10 @@ impl Engine {
         &self.modules
     }
 
+    pub fn set_strict_builtin_errors(&mut self, b: bool) {
+        self.interpreter.set_strict_builtin_errors(b)
+    }
+
     fn prepare_for_eval(&mut self, enable_tracing: bool) -> Result<()> {
         self.interpreter.set_traces(enable_tracing);
 
diff --git a/src/interpreter.rs b/src/interpreter.rs
index b83947c..79ab322 100644
--- a/src/interpreter.rs
+++ b/src/interpreter.rs
@@ -44,6 +44,7 @@ pub struct Interpreter {
     no_rules_lookup: bool,
     traces: Option<Vec<std::rc::Rc<str>>>,
     allow_deprecated: bool,
+    strict_builtin_errors: bool,
 }
 
 impl Default for Interpreter {
@@ -130,6 +131,7 @@ impl Interpreter {
             no_rules_lookup: false,
             traces: None,
             allow_deprecated: true,
+            strict_builtin_errors: true,
         }
     }
 
@@ -168,14 +170,18 @@ impl Interpreter {
         };
     }
 
+    pub fn set_strict_builtin_errors(&mut self, b: bool) {
+        self.strict_builtin_errors = b;
+    }
+
     pub fn set_input(&mut self, input: Value) {
         self.input = input;
         info!("input: {:#?}", self.input);
     }
 
     pub fn init_with_document(&mut self) -> Result<()> {
-        *Self::make_or_get_value_mut(&mut self.with_document, &["data"])? = Value::new_object();
-        *Self::make_or_get_value_mut(&mut self.with_document, &["input"])? = Value::new_object();
+        *Self::make_or_get_value_mut(&mut self.with_document, &["data"])? = self.init_data.clone();
+        *Self::make_or_get_value_mut(&mut self.with_document, &["input"])? = self.input.clone();
 
         Ok(())
     }
@@ -789,6 +795,7 @@ impl Interpreter {
             // OPA raises the error sometimes in static scenarios, but doesn't
             // raise in scenarios due to data/input
             (Expr::Array { .. }, _) | (Expr::Object { .. }, _) => Ok(false),
+
             _ => {
                 let expr_value = self.lookup_or_eval_expr(cache, expr)?;
                 if expr_value == Value::Undefined {
@@ -1096,18 +1103,28 @@ impl Interpreter {
                 };
 
                 if path[0] == "input" || path[0] == "data" {
+                    if path.len() > 1 {
+                        let vref =
+                            Self::make_or_get_value_mut(&mut self.with_document, &path[0..1])?;
+                        match *vref {
+                            Value::Object(_) => (),
+                            _ => *vref = Value::new_object(),
+                        }
+                    }
+
                     *Self::make_or_get_value_mut(&mut self.with_document, &path[..])? = value;
-                } /* else if path.len() == 1 {
-                      // TODO: handle var in current module.
-                  } else {
-                      // TODO: error about input, data
-                  } */
+                }
+
+                /* else if path.len() == 1 {
+                    // TODO: handle var in current module.
+                } else {
+                    // TODO: error about input, data
+                } */
             }
 
             self.data = self.with_document["data"].clone();
             self.input = self.with_document["input"].clone();
             self.processed.clear();
-
             (with_document, input, data, processed, with_functions)
         } else {
             (
@@ -1651,7 +1668,7 @@ impl Interpreter {
             }
         }
 
-        let v = builtin.0(span, params, &args[..])?;
+        let v = builtin.0(span, params, &args[..], self.strict_builtin_errors)?;
 
         // Handle trace function.
         // TODO: with modifier.
@@ -1694,18 +1711,29 @@ impl Interpreter {
             _ => orig_fcn_path.clone(),
         };
 
+        let empty = vec![];
         let fcns_rules = match self.lookup_function_by_name(&fcn_path) {
             Some(r) => r,
             _ => {
+                if self.default_rules.get(&fcn_path).is_some()
+                    || self
+                        .default_rules
+                        .get(&get_path_string(fcn, Some(&self.current_module_path))?)
+                        .is_some()
+                {
+                    // process default functions later.
+                    &empty
+                }
                 // Look up builtin function.
-                if let Ok(Some(builtin)) = self.lookup_builtin(span, &fcn_path) {
+                else if let Ok(Some(builtin)) = self.lookup_builtin(span, &fcn_path) {
                     let r = self.eval_builtin_call(span, &fcn_path.clone(), *builtin, params);
                     if orig_fcn_path != fcn_path {
                         self.with_functions.insert(orig_fcn_path, fcn_path);
                     }
                     return r;
+                } else {
+                    bail!(span.error(format!("could not find function {fcn_path}").as_str()));
                 }
-                bail!(span.error(format!("could not find function {fcn_path}").as_str()));
             }
         };
 
@@ -1757,10 +1785,10 @@ impl Interpreter {
             let mut type_match = BTreeSet::new();
 
             for (idx, a) in args.iter().enumerate() {
-                if self
-                    .make_bindings(false, &mut type_match, &mut cache, a, &param_values[idx])
-                    .is_err()
-                {
+                let b =
+                    self.make_bindings(false, &mut type_match, &mut cache, a, &param_values[idx]);
+
+                if b.ok() != Some(true) {
                     self.scopes = scopes;
                     continue 'outer;
                 }
@@ -1799,7 +1827,9 @@ impl Interpreter {
 
                 // If the function execution resulted in undefined, then propagate it.
                 Value::Undefined => Value::Undefined,
-                _ => bail!("internal error: function did not return set {value:?}"),
+
+                // Function returned a non set value
+                v => v.clone(),
             };
 
             // Restore local variables for current context.
@@ -1810,6 +1840,34 @@ impl Interpreter {
             }
         }
 
+        if results.is_empty() {
+            // Back up local variables of current function and empty
+            // the local variables of callee function.
+            let scopes = std::mem::take(&mut self.scopes);
+            if errors.is_empty() {
+                // Check if any default rules can be evaluated.
+                // TODO: with mod
+                let rules = match self.default_rules.get(&fcn_path).cloned() {
+                    Some(rules) => Some(rules),
+                    None => {
+                        let fcn_path = get_path_string(fcn, Some(&self.current_module_path))?;
+                        self.default_rules.get(&fcn_path).cloned()
+                    }
+                };
+                if let Some(rules) = rules {
+                    for (rule, _) in rules.iter() {
+                        if let Rule::Default { value, .. } = rule.as_ref() {
+                            match self.eval_expr(value) {
+                                Ok(v) => results.push(v),
+                                Err(e) => errors.push(e),
+                            }
+                        }
+                    }
+                }
+            }
+            self.scopes = scopes;
+        }
+
         if results.is_empty() {
             if errors.is_empty() {
                 return Ok(Value::Undefined);
@@ -1937,15 +1995,28 @@ impl Interpreter {
                 return Ok(v);
             }
 
-            // Evaluate rule corresponding to longest matching path.
-            for i in (1..fields.len() + 1).rev() {
+            if fields.is_empty() {
+                bail!(span.error("this results in recursive evaluation of data."))
+            }
+
+            // Find the rule to which the var being looked up corresponds to. This is the prefix for
+            // which rules exist.
+            let mut found = false;
+            for i in 1..fields.len() + 1 {
                 let path = "data.".to_owned() + &fields[0..i].join(".");
                 if self.rules.get(&path).is_some() || self.default_rules.get(&path).is_some() {
                     self.ensure_rule_evaluated(path)?;
+                    found = true;
                     break;
                 }
             }
 
+            // TODO: emit this error only if the var can belong to a rego module; not data specified via json/yaml.
+            //if !no_error && !found {
+            //    bail!(span.error("var is unsafe"));
+            //}
+            let _ = found;
+
             Ok(Self::get_value_chained(self.data.clone(), fields))
         } else if !self.modules.is_empty() {
             let path = Parser::get_path_ref_components(&self.module.clone().unwrap().package.refr)?;
@@ -1960,10 +2031,8 @@ impl Interpreter {
                 return Ok(v);
             }
 
-            // Add module prefix and ensure that any matching rule is evaluated.
-            let module_path =
-                Self::get_path_string(&self.current_module()?.package.refr, Some("data"))?;
-            let rule_path = module_path + "." + name.text();
+            // Ensure that all the rules having common prefix (name) are evaluated.
+            let rule_path = "data.".to_owned() + &path.join(".");
 
             if !no_error
                 && self.rules.get(&rule_path).is_none()
@@ -1971,6 +2040,7 @@ impl Interpreter {
             {
                 bail!(span.error("var is unsafe"));
             }
+
             self.ensure_rule_evaluated(rule_path)?;
 
             let value = Self::get_value_chained(self.data.clone(), &path[..]);
@@ -2318,9 +2388,18 @@ impl Interpreter {
         }
 
         if let Rule::Default {
-            span, refr, value, ..
+            span,
+            refr,
+            value,
+            args,
+            ..
         } = rule.as_ref()
         {
+            if !args.is_empty() {
+                // Non-zero function defaults are evaluated differently.
+                return Ok(());
+            }
+
             let scopes = std::mem::take(&mut self.scopes);
 
             let mut path =
@@ -2588,8 +2667,10 @@ impl Interpreter {
                         Expr::RefBrack { refr, .. } => refr,
                         _ => refr,
                     };
-                    let path = Self::get_path_string(refr, None)?;
-                    let path = self.current_module_path.clone() + "." + &path;
+                    //let path = Self::get_path_string(refr, None)?;
+                    let path = get_root_var(refr)?;
+                    let path = path.text();
+                    let path = self.current_module_path.clone() + "." + path;
                     match self.rules.entry(path) {
                         Entry::Occupied(o) => {
                             o.into_mut().push(rule.clone());
@@ -2617,8 +2698,10 @@ impl Interpreter {
                         _ => (refr, None),
                     };
 
-                    let path = Self::get_path_string(refr, None)?;
-                    let path = self.current_module_path.clone() + "." + &path;
+                    //let path = Self::get_path_string(refr, None)?;
+                    let path = get_root_var(refr)?;
+                    let path = path.text();
+                    let path = self.current_module_path.clone() + "." + path;
                     match self.default_rules.entry(path) {
                         Entry::Occupied(o) => {
                             for (_, i) in o.get() {
diff --git a/src/parser.rs b/src/parser.rs
index 942aac0..1618b85 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -209,7 +209,9 @@ impl<'source> Parser<'source> {
         match self.tok.0 {
             TokenKind::Ident
                 if self.is_keyword(*span.text())
-                    || self.is_imported_future_keyword(*span.text()) =>
+                    || (self.is_imported_future_keyword(*span.text())
+		    // contains can be the name of a builtin even when a keyword
+		    && *span.text() != "contains") =>
             {
                 Err(self.source.error(
                     self.tok.1.line,
@@ -1425,6 +1427,25 @@ impl<'source> Parser<'source> {
         self.expect("default", "while parsing default rule")?;
         let rule_ref = Ref::new(self.parse_rule_ref()?);
 
+        let mut args = vec![];
+        if *self.token_text() == "(" {
+            self.next_token()?;
+            if *self.token_text() != ")" {
+                loop {
+                    let arg = self.parse_ident()?;
+                    if *arg.text() != "_" && args.iter().any(|a: &Span| *a.text() == *arg.text()) {
+                        bail!(arg.error("repeating parameter name"));
+                    }
+                    args.push(arg);
+                    if *self.token_text() == ")" || self.tok.0 == TokenKind::Eof {
+                        break;
+                    }
+                    self.expect(",", "while parsing default rule parameters")?;
+                }
+            }
+            self.expect(")", "while parsing default rule parameters")?;
+        }
+
         let op = match *self.token_text() {
             "=" => AssignOp::Eq,
             ":=" => AssignOp::ColEq,
@@ -1443,6 +1464,7 @@ impl<'source> Parser<'source> {
         Ok(Rule::Default {
             span,
             refr: rule_ref,
+            args: args.into_iter().map(|a| Ref::new(Expr::Var(a))).collect(),
             op,
             value,
         })
diff --git a/src/scheduler.rs b/src/scheduler.rs
index 7f632c9..9de2625 100644
--- a/src/scheduler.rs
+++ b/src/scheduler.rs
@@ -205,7 +205,8 @@ pub fn schedule<Str: Clone + std::cmp::Ord + std::fmt::Debug>(
 
 #[derive(Clone, Default, Debug)]
 pub struct Scope {
-    pub locals: BTreeSet<SourceStr>,
+    pub locals: BTreeMap<SourceStr, Span>,
+    pub unscoped: BTreeSet<SourceStr>,
     pub inputs: BTreeSet<SourceStr>,
 }
 
@@ -269,8 +270,24 @@ fn traverse(expr: &Ref<Expr>, f: &mut dyn FnMut(&Ref<Expr>) -> Result<bool>) ->
     Ok(())
 }
 
-fn var_exists(name: &SourceStr, parent_scopes: &[Scope]) -> bool {
-    parent_scopes.iter().rev().any(|s| s.locals.contains(name))
+fn var_exists(var: &Span, parent_scopes: &[Scope]) -> bool {
+    let name = var.source_str();
+
+    for pscope in parent_scopes.iter().rev() {
+        if pscope.unscoped.contains(&name) {
+            return true;
+        }
+        // Check parent scope vars defined using :=.
+        if let Some(s) = pscope.locals.get(&name) {
+            // Note: Since a rule cannot span multiple files, it is safe to check only
+            // the line numbers.
+            if s.line <= var.line {
+                // The variable was defined in parent scope prior to current comprehension.
+                return true;
+            }
+        }
+    }
+    false
 }
 
 fn gather_assigned_vars(
@@ -285,19 +302,19 @@ fn gather_assigned_vars(
 
         // Record local var that can shadow input var.
         Var(v) if can_shadow => {
-            scope.locals.insert(v.source_str());
+            scope.locals.insert(v.source_str(), v.clone());
             Ok(false)
         }
 
         // Record input vars.
-        Var(v) if var_exists(&v.source_str(), parent_scopes) => {
+        Var(v) if var_exists(v, parent_scopes) => {
             scope.inputs.insert(v.source_str());
             Ok(false)
         }
 
         // Record local var.
         Var(v) => {
-            scope.locals.insert(v.source_str());
+            scope.unscoped.insert(v.source_str());
             Ok(false)
         }
 
@@ -309,11 +326,8 @@ fn gather_assigned_vars(
 
 fn gather_input_vars(expr: &Ref<Expr>, parent_scopes: &[Scope], scope: &mut Scope) -> Result<()> {
     traverse(expr, &mut |e| match e.as_ref() {
-        Var(v) if var_exists(&v.source_str(), parent_scopes) => {
-            let var = v.source_str();
-            if !scope.locals.contains(&var) {
-                scope.inputs.insert(var);
-            }
+        Var(v) if !scope.unscoped.contains(&v.source_str()) && var_exists(v, parent_scopes) => {
+            scope.inputs.insert(v.source_str());
             Ok(false)
         }
         _ => Ok(true),
@@ -322,14 +336,12 @@ fn gather_input_vars(expr: &Ref<Expr>, parent_scopes: &[Scope], scope: &mut Scop
 
 fn gather_loop_vars(expr: &Ref<Expr>, parent_scopes: &[Scope], scope: &mut Scope) -> Result<()> {
     traverse(expr, &mut |e| match e.as_ref() {
-        Var(v) if var_exists(&v.source_str(), parent_scopes) => Ok(false),
+        Var(v) if var_exists(v, parent_scopes) => Ok(false),
         RefBrack { index, .. } => {
             if let Var(v) = index.as_ref() {
-                if !matches!(*v.text(), "_" | "input" | "data")
-                    && !var_exists(&v.source_str(), parent_scopes)
-                {
+                if !matches!(*v.text(), "_" | "input" | "data") && !var_exists(v, parent_scopes) {
                     // Treat this as an index var.
-                    scope.locals.insert(v.source_str());
+                    scope.unscoped.insert(v.source_str());
                 }
             }
             Ok(true)
@@ -367,7 +379,7 @@ fn gather_vars(
 
 pub struct Analyzer {
     packages: BTreeMap<String, Scope>,
-    locals: BTreeMap<Ref<Query>, Scope>,
+    scope_table: BTreeMap<Ref<Query>, Scope>,
     scopes: Vec<Scope>,
     order: BTreeMap<Ref<Query>, Vec<u16>>,
     functions: FunctionTable,
@@ -390,7 +402,7 @@ impl Analyzer {
     pub fn new() -> Analyzer {
         Analyzer {
             packages: BTreeMap::new(),
-            locals: BTreeMap::new(),
+            scope_table: BTreeMap::new(),
             scopes: vec![],
             order: BTreeMap::new(),
             functions: FunctionTable::new(),
@@ -407,7 +419,7 @@ impl Analyzer {
         }
 
         Ok(Schedule {
-            scopes: self.locals,
+            scopes: self.scope_table,
             order: self.order,
         })
     }
@@ -421,7 +433,7 @@ impl Analyzer {
         self.analyze_query(None, None, query, Scope::default())?;
 
         Ok(Schedule {
-            scopes: self.locals,
+            scopes: self.scope_table,
             order: self.order,
         })
     }
@@ -441,7 +453,7 @@ impl Analyzer {
                         ..
                     } => get_root_var(refr)?,
                 };
-                scope.locals.insert(var);
+                scope.unscoped.insert(var);
             }
         }
 
@@ -529,9 +541,12 @@ impl Analyzer {
             RuleHead::Set { key, .. } => (key.clone(), None, scope),
             RuleHead::Func { args, assign, .. } => {
                 for a in args.iter() {
-                    if let Var(v) = a.as_ref() {
-                        scope.locals.insert(v.source_str());
-                    }
+                    traverse(a, &mut |e| {
+                        if let Var(v) = e.as_ref() {
+                            scope.unscoped.insert(v.source_str());
+                        }
+                        Ok(true)
+                    })?;
                 }
                 (None, assign.as_ref().map(|a| a.value.clone()), scope)
             }
@@ -549,7 +564,7 @@ impl Analyzer {
         for stmt in &query.stmts {
             match &stmt.literal {
                 Literal::SomeVars { vars, .. } => vars.iter().for_each(|v| {
-                    scope.locals.insert(v.source_str());
+                    scope.locals.insert(v.source_str(), v.clone());
                 }),
                 Literal::SomeIn {
                     key,
@@ -597,8 +612,9 @@ impl Analyzer {
         }
 
         // Remove input vars that are shadowed.
-        for v in &scope.locals {
+        for v in scope.locals.keys() {
             scope.inputs.remove(v);
+            scope.unscoped.remove(v);
         }
 
         Ok(())
@@ -621,7 +637,7 @@ impl Analyzer {
                     _ => false,
                 };
 
-                if scope.locals.contains(&name)
+                if scope.locals.contains_key(&name) || scope.unscoped.contains(&name)
                 /*|| scope.inputs.contains(name) */
                 {
                     if !is_extra_arg {
@@ -637,7 +653,7 @@ impl Analyzer {
             RefBrack { refr, index, .. } => {
                 if let Var(v) = index.as_ref() {
                     let var = v.source_str();
-                    if scope.locals.contains(&var) {
+                    if scope.locals.contains_key(&var) || scope.unscoped.contains(&var) {
                         let (rb_used_vars, rb_comprs) = Self::gather_used_vars_comprs_index_vars(
                             refr,
                             scope,
@@ -681,7 +697,7 @@ impl Analyzer {
             let compr_scope = match compr.as_ref() {
                 Expr::ArrayCompr { query, term, .. } | Expr::SetCompr { query, term, .. } => {
                     self.analyze_query(None, Some(term.clone()), query, Scope::default())?;
-                    self.locals.get(query)
+                    self.scope_table.get(query)
                 }
                 Expr::ObjectCompr {
                     query, key, value, ..
@@ -692,7 +708,7 @@ impl Analyzer {
                         query,
                         Scope::default(),
                     )?;
-                    self.locals.get(query)
+                    self.scope_table.get(query)
                 }
                 _ => break,
             };
@@ -700,7 +716,7 @@ impl Analyzer {
             // Record vars used by the comprehension scope.
             if let Some(compr_scope) = compr_scope {
                 for iv in &compr_scope.inputs {
-                    if scope.locals.contains(iv) {
+                    if scope.locals.contains_key(iv) || scope.unscoped.contains(iv) {
                         // Record possible first use of current scope's local var.
                         first_use.entry(iv.clone()).or_insert(compr.span().clone());
                         used_vars.push(iv.clone());
@@ -727,11 +743,13 @@ impl Analyzer {
         traverse(expr, &mut |e| match e.as_ref() {
             Var(v) => {
                 let var = v.source_str();
-                if scope.locals.contains(&var) {
+                if scope.locals.contains_key(&var) {
                     if check_first_use {
                         Self::check_first_use(v, first_use)?;
                     }
                     vars.push(var);
+                } else if scope.unscoped.contains(&var) {
+                    vars.push(var);
                 }
                 Ok(false)
             }
@@ -890,7 +908,7 @@ impl Analyzer {
         non_vars: &mut Vec<Ref<Expr>>,
     ) -> Result<()> {
         traverse(expr, &mut |e| match e.as_ref() {
-            Var(v) if scope.locals.contains(&v.source_str()) => {
+            Var(v) if scope.locals.contains_key(&v.source_str()) => {
                 vars.push(v.source_str());
                 Ok(false)
             }
@@ -1012,8 +1030,8 @@ impl Analyzer {
                         let mut extras_scope = Scope::default();
                         gather_assigned_vars(ea, false, &self.scopes, &mut extras_scope)?;
 
-                        for var in &extras_scope.locals {
-                            scope.locals.insert(var.clone());
+                        for var in &extras_scope.unscoped {
+                            scope.unscoped.insert(var.clone());
                         }
 
                         // Gather vars being used.
@@ -1022,7 +1040,7 @@ impl Analyzer {
                             &mut scope,
                             &mut first_use,
                             &mut definitions,
-                            &Some(&extras_scope.locals),
+                            &Some(&extras_scope.unscoped),
                         )?;
 
                         self.process_comprs(
@@ -1032,8 +1050,8 @@ impl Analyzer {
                             &mut used_vars,
                         )?;
 
-                        if !extras_scope.locals.is_empty() {
-                            for var in extras_scope.locals {
+                        if !extras_scope.unscoped.is_empty() {
+                            for var in extras_scope.unscoped {
                                 definitions.push(Definition {
                                     var,
                                     used_vars: used_vars.clone(),
@@ -1076,9 +1094,9 @@ impl Analyzer {
                     self.scopes.push(scope.clone());
                     let mut e_scope = Scope::default();
                     if let Some(key) = key {
-                        e_scope.locals.insert(key.source_str());
+                        e_scope.locals.insert(key.source_str(), key.clone());
                     }
-                    e_scope.locals.insert(value.source_str());
+                    e_scope.locals.insert(value.source_str(), value.clone());
                     self.scopes.push(e_scope);
 
                     // TODO: mark first use of key, value so that they cannot be := assigned
@@ -1112,7 +1130,7 @@ impl Analyzer {
             }
             _ => (),
         }
-        self.locals.insert(query.clone(), scope);
+        self.scope_table.insert(query.clone(), scope);
 
         Ok(())
     }
diff --git a/tests/opa.passing b/tests/opa.passing
index d6f0591..69768f4 100644
--- a/tests/opa.passing
+++ b/tests/opa.passing
@@ -10,33 +10,50 @@ bitsor
 bitsshiftleft
 bitsshiftright
 bitsxor
+casts
 comparisonexpr
 completedoc
 compositebasedereference
-dataderef
+comprehensions
+containskeyword
 cryptohmacequal
-cryptohmacmd5 
+cryptohmacmd5
 cryptohmacsha1
 cryptohmacsha256
 cryptohmacsha512
 cryptomd5
-cryptsha1
+cryptosha1
 cryptosha256
+dataderef
+disjunction
+elsekeyword
 embeddedvirtualdoc
 evaltermexpr
+every
 example
 fix1863
+functionerrors
+functions
 globmatch
+globquotemeta
 helloworld
 indexing
+indirectreferences
 intersection
 invalidkeyerror
 jsonfilteridempotent
+jwtencodesignheadererrors
+jwtencodesignpayloaderrors
 nestedreferences
+objectfilter
 objectfilteridempotent
 objectfilternonstringkey
+objectget
+objectkeys
+objectremove
 objectremoveidempotent
 objectremovenonstringkey
+partialdocconstants
 partialsetdoc
 rand
 regexfind
@@ -57,6 +74,7 @@ trimprefix
 trimright
 trimspace
 trimsuffix
+type
 typebuiltin
 typenamebuiltin
 undos
diff --git a/tests/opa.rs b/tests/opa.rs
index fbe2466..f93b380 100644
--- a/tests/opa.rs
+++ b/tests/opa.rs
@@ -16,18 +16,33 @@ const OPA_REPO: &str = "https://github.com/open-policy-agent/opa";
 const OPA_BRANCH: &str = "v0.58.0";
 
 #[derive(Serialize, Deserialize, PartialEq, Debug)]
+#[serde(deny_unknown_fields)]
 struct TestCase {
+    #[serde(skip_serializing_if = "Option::is_none")]
     data: Option<Value>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     input: Option<Value>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    input_term: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     modules: Option<Vec<String>>,
     note: String,
     query: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
     sort_bindings: Option<bool>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     want_result: Option<Value>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     skip: Option<bool>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     error: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     traces: Option<bool>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    strict_error: Option<bool>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     want_error: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     want_error_code: Option<String>,
 }
 
@@ -45,11 +60,18 @@ fn eval_test_case(case: &TestCase) -> Result<Value> {
     if let Some(input) = &case.input {
         engine.set_input(input.clone());
     }
+    if let Some(input_term) = &case.input_term {
+        let input = Value::from_json_str(&input_term)?;
+        engine.set_input(input);
+    }
     if let Some(modules) = &case.modules {
         for (idx, rego) in modules.iter().enumerate() {
             engine.add_policy(format!("rego{idx}.rego"), rego.clone())?;
         }
     }
+
+    engine.set_strict_builtin_errors(case.strict_error.unwrap_or_default());
+
     let query_results = engine.eval_query(case.query.clone(), true)?;
 
     let mut values = vec![];
@@ -182,9 +204,11 @@ fn run_opa_tests(opa_tests_dir: String, folders: &[String]) -> Result<()> {
     println!("\nOPA TESTSUITE STATUS");
     println!("    {:40}  {:4} {:4}", "FOLDER", "PASS", "FAIL");
     let (mut npass, mut nfail) = (0, 0);
+    let mut passing = vec![];
     for (dir, (pass, fail)) in status {
         if fail == 0 {
             println!("\x1b[32m    {dir:40}: {pass:4} {fail:4}\x1b[0m");
+            passing.push(dir);
         } else {
             println!("\x1b[31m    {dir:40}: {pass:4} {fail:4}\x1b[0m");
         }
@@ -193,6 +217,8 @@ fn run_opa_tests(opa_tests_dir: String, folders: &[String]) -> Result<()> {
     }
     println!();
 
+    std::fs::write("target/opa.passing", passing.join("\n"))?;
+
     if npass == 0 && nfail == 0 {
         bail!("no matching tests found.");
     } else if nfail == 0 {
diff --git a/tests/parser/mod.rs b/tests/parser/mod.rs
index 317b3b7..eecf189 100644
--- a/tests/parser/mod.rs
+++ b/tests/parser/mod.rs
@@ -569,12 +569,14 @@ fn match_rule(r: &Rule, v: &Value) -> Result<()> {
         Rule::Default {
             span,
             refr,
+            args,
             op,
             value,
         } => {
             let obj = &v["default"];
             match_span_opt(span, &obj["span"])?;
             match_expr(refr, &obj["refr"])?;
+            match_vec(span /*dummy*/, args, &obj["args"])?;
             match_assign_op(span, op, &obj["op"])?;
             match_expr(value, &obj["value"])
         }
diff --git a/tests/scheduler/analyzer/basic.yaml b/tests/scheduler/analyzer/basic.yaml
index 562a271..a920f2d 100644
--- a/tests/scheduler/analyzer/basic.yaml
+++ b/tests/scheduler/analyzer/basic.yaml
@@ -37,9 +37,12 @@ cases:
         r = 1
         rrr = "fun"
     scopes:
-      - locals: ["p", "y", "q", "x", "a", "b", "idx"]
+      - locals: ["x"]
+        unscoped: ["p", "y", "q", "a", "b", "idx"]
         inputs: ["r", "rrr"]
-      - locals: ["k", "r1"]
+      - locals: []
+        unscoped: ["k", "r1"]
         inputs: ["a", "idx", "rrr"]
-      - locals: ["q", "idx1", "t"]
+      - locals: ["q"]
+        unscoped: ["idx1", "t"]
         inputs: ["rrr"]
diff --git a/tests/scheduler/analyzer/mod.rs b/tests/scheduler/analyzer/mod.rs
index cda57cf..0be7e57 100644
--- a/tests/scheduler/analyzer/mod.rs
+++ b/tests/scheduler/analyzer/mod.rs
@@ -12,6 +12,7 @@ use std::collections::BTreeSet;
 #[derive(Serialize, Deserialize, PartialEq, Debug)]
 struct Scope {
     pub locals: BTreeSet<String>,
+    pub unscoped: BTreeSet<String>,
     pub inputs: BTreeSet<String>,
 }
 
@@ -27,8 +28,11 @@ struct YamlTest {
     cases: Vec<TestCase>,
 }
 
-fn to_string_set(s: &BTreeSet<SourceStr>) -> BTreeSet<String> {
-    s.iter().map(|s| s.to_string()).collect()
+fn to_string_set<'a, I>(itr: I) -> BTreeSet<String>
+where
+    I: std::iter::Iterator<Item = &'a SourceStr>,
+{
+    itr.map(|s| s.to_string()).collect()
 }
 
 fn analyze_file(regos: &[String], expected_scopes: &[Scope]) -> Result<()> {
@@ -55,8 +59,18 @@ fn analyze_file(regos: &[String], expected_scopes: &[Scope]) -> Result<()> {
         if idx > expected_scopes.len() {
             bail!("extra scope generated.")
         }
-        assert_eq!(to_string_set(&scope.locals), expected_scopes[idx].locals);
-        assert_eq!(to_string_set(&scope.inputs), expected_scopes[idx].inputs);
+        assert_eq!(
+            to_string_set(scope.locals.keys()),
+            expected_scopes[idx].locals
+        );
+        assert_eq!(
+            to_string_set(scope.unscoped.iter()),
+            expected_scopes[idx].unscoped
+        );
+        assert_eq!(
+            to_string_set(scope.inputs.iter()),
+            expected_scopes[idx].inputs
+        );
         println!("scope {idx} matched.")
     }