added a has-key and has-value builtin to test the existence of an ele…

…ment.

fixes #407 #398

eval/builtin_fn.go

@@ -112,6 +112,8 @@ func init() {
 		{"take", take},
 		{"range", rangeFn},
 		{"count", count},
+		{"has-key", hasKey},
+		{"has-value", hasValue},
 
 		// String
 		{"joins", joins},
@@ -780,6 +782,57 @@ func rangeFn(ec *EvalCtx, args []Value, opts map[string]Value) {
 	}
 }
 
+func hasValue(ec *EvalCtx, args []Value, opts map[string]Value) {
+	TakeNoOpt(opts)
+
+	var found bool
+	if len(args) == 2 {
+		v := args[0]
+		if iterator, ok := v.(Iterable); ok {
+			iterator.Iterate(func(v Value) bool {
+				if v == args[1] {
+					found = true
+					return false
+				}
+				return true
+			})
+		} else {
+			throw(fmt.Errorf("argument of type '%s' is not iterable", v.Kind()))
+		}
+	} else {
+		throw(errors.New("want 2 arguments"))
+	}
+
+	ec.ports[1].Chan <- Bool(found)
+}
+
+func hasKey(ec *EvalCtx, args []Value, opts map[string]Value) {
+	TakeNoOpt(opts)
+
+	var found bool
+	if len(args) == 2 {
+		v := args[0]
+		switch val := v.(type) {
+		case HasKeyer:
+			if val.HasKey(args[1]) {
+				found = true
+			}
+		case Lener:
+			if err := util.PCall(func() {
+				ParseAndFixListIndex(ToString(args[1]), val.Len())
+			}); err == nil {
+				found = true
+			}
+		default:
+			throw(fmt.Errorf("couldn't get key or index of type '%s'", v.Kind()))
+		}
+	} else {
+		throw(errors.New("want 2 arguments"))
+	}
+
+	ec.ports[1].Chan <- Bool(found)
+}
+
 func count(ec *EvalCtx, args []Value, opts map[string]Value) {
 	TakeNoOpt(opts)