strings: concat and contains

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

src/builtins/strings.rs

@@ -13,6 +13,7 @@ use anyhow::Result;
 
 pub fn register(m: &mut HashMap<&'static str, builtins::BuiltinFcn>) {
     m.insert("concat", concat);
+    m.insert("contains", contains);
 }
 
 fn concat(span: &Span, params: &[Expr], args: &[Value]) -> Result<Value> {
@@ -22,3 +23,11 @@ fn concat(span: &Span, params: &[Expr], args: &[Value]) -> Result<Value> {
     let collection = ensure_string_collection(name, &params[1], &args[1])?;
     Ok(Value::String(collection.join(&delimiter)))
 }
+
+fn contains(span: &Span, params: &[Expr], args: &[Value]) -> Result<Value> {
+    let name = "contains";
+    ensure_args_count(span, name, params, args, 2)?;
+    let s1 = ensure_string(name, &params[0], &args[0])?;
+    let s2 = ensure_string(name, &params[1], &args[1])?;
+    Ok(Value::Bool(s1.contains(&s2)))
+}