Update argument type of set expr function

It changes 3rd argument type os set expr function from TypedValue to interface, since GvalParser parses argument to native types before evaluating the expression.

pkg/expr/parser_test.go

@@ -6,6 +6,12 @@ import (
 	"testing"
 )
 
+func Example_simpleExpression() {
+	eval(`40 + 2`, nil)
+	// output:
+	// 42
+}
+
 func TestParser(t *testing.T) {
 	var (
 		req    = require.New(t)
@@ -23,8 +29,24 @@ func TestParser(t *testing.T) {
 	req.True(result)
 }
 
-func Example_simpleExpresion() {
-	eval(`40 + 2`, nil)
-	// output:
-	// 42
+func TestGvalParser(t *testing.T) {
+	var (
+		req     = require.New(t)
+		ctx     = context.Background()
+		p       = NewGvalParser()
+		vv, err = NewVars(map[string]interface{}{
+			"vars":  &Vars{},
+			"key":   "foo",
+			"value": Must(NewString("foo")),
+		})
+		result interface{}
+	)
+	req.NoError(err)
+
+	pp, err := p.Parse("toJSON(set(vars, key, value))")
+	req.NoError(err)
+
+	result, err = pp.Eval(ctx, vv)
+	req.NoError(err)
+	req.Equal("{\"foo\":{\"@value\":\"foo\",\"@type\":\"String\"}}", result)
 }