From 90aafc8bb403baf8d87bafda0354aa829c27e964 Mon Sep 17 00:00:00 2001
From: Daniel Kang <me@daniel.gs>
Date: Sun, 3 Feb 2019 15:50:40 -0800
Subject: [PATCH] Add 'is_function' and 'is_callable' builtin functions

---
 docs/builtins.md               | 24 ++++++++++++++++--------
 objects/builtin_type_checks.go | 26 ++++++++++++++++++++++++++
 objects/builtins.go            |  8 ++++++++
 runtime/vm_builtin_test.go     | 21 +++++++++++++++++++++
 4 files changed, 71 insertions(+), 8 deletions(-)

diff --git a/docs/builtins.md b/docs/builtins.md
index 68b3ba1..a4f8c6b 100644
--- a/docs/builtins.md
+++ b/docs/builtins.md
@@ -185,32 +185,40 @@ v := bytes(100)
 
 ## is_string
 
-Returns `true` if the object is string. Or it returns `false`.
+Returns `true` if the object's type is string. Or it returns `false`.
 
 ## is_int
 
-Returns `true` if the object is int. Or it returns `false`.
+Returns `true` if the object's type is int. Or it returns `false`.
 
 ## is_bool
 
-Returns `true` if the object is bool. Or it returns `false`.
+Returns `true` if the object's type is bool. Or it returns `false`.
 
 ## is_float
 
-Returns `true` if the object is float. Or it returns `false`.
+Returns `true` if the object's type is float. Or it returns `false`.
 
 ## is_char
 
-Returns `true` if the object is char. Or it returns `false`.
+Returns `true` if the object's type is char. Or it returns `false`.
 
 ## is_bytes
 
-Returns `true` if the object is bytes. Or it returns `false`.
+Returns `true` if the object's type is bytes. Or it returns `false`.
 
 ## is_error
 
-Returns `true` if the object is error. Or it returns `false`.
+Returns `true` if the object's type is error. Or it returns `false`.
 
 ## is_undefined
 
-Returns `true` if the object is undefined. Or it returns `false`.
\ No newline at end of file
+Returns `true` if the object's type is undefined. Or it returns `false`.
+
+## is_function
+
+Returns `true` if the object's type is function or closure. Or it returns `false`. Note that `is_function` returns `false` for builtin functions and user-provided callable objects. 
+
+## is_callable
+
+Returns `true` if the object is callable (e.g. function, closure, builtin function, or user-provided callable objects). Or it returns `false`.
\ No newline at end of file
diff --git a/objects/builtin_type_checks.go b/objects/builtin_type_checks.go
index e39cc9f..960f782 100644
--- a/objects/builtin_type_checks.go
+++ b/objects/builtin_type_checks.go
@@ -155,3 +155,29 @@ func builtinIsUndefined(args ...Object) (Object, error) {
 
 	return FalseValue, nil
 }
+
+func builtinIsFunction(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	switch args[0].(type) {
+	case *CompiledFunction, *Closure:
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
+
+func builtinIsCallable(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	switch args[0].(type) {
+	case *CompiledFunction, *Closure, Callable: // BuiltinFunction is Callable
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
diff --git a/objects/builtins.go b/objects/builtins.go
index 30049e9..6755393 100644
--- a/objects/builtins.go
+++ b/objects/builtins.go
@@ -112,6 +112,14 @@ var Builtins = []NamedBuiltinFunc{
 		Name: "is_undefined",
 		Func: builtinIsUndefined,
 	},
+	{
+		Name: "is_function",
+		Func: builtinIsFunction,
+	},
+	{
+		Name: "is_callable",
+		Func: builtinIsCallable,
+	},
 	{
 		Name: "to_json",
 		Func: builtinToJSON,
diff --git a/runtime/vm_builtin_test.go b/runtime/vm_builtin_test.go
index 0eef432..841f789 100644
--- a/runtime/vm_builtin_test.go
+++ b/runtime/vm_builtin_test.go
@@ -172,4 +172,25 @@ func TestBuiltinFunction(t *testing.T) {
 	expect(t, `out = type_name(bytes( 1))`, "bytes")
 	expect(t, `out = type_name(undefined)`, "undefined")
 	expect(t, `out = type_name(error("err"))`, "error")
+	expect(t, `out = type_name(func() {})`, "compiled-function")
+	expect(t, `a := func(x) { return func() { return x } }; out = type_name(a(5))`, "closure") // closure
+
+	// is_function
+	expect(t, `out = is_function(1)`, false)
+	expect(t, `out = is_function(func() {})`, true)
+	expect(t, `out = is_function(func(x) { return x })`, true)
+	expect(t, `out = is_function(len)`, false)                                                                 // builtin function
+	expect(t, `a := func(x) { return func() { return x } }; out = is_function(a)`, true)                       // function
+	expect(t, `a := func(x) { return func() { return x } }; out = is_function(a(5))`, true)                    // closure
+	expectWithSymbols(t, `out = is_function(x)`, false, SYM{"x": &StringArray{Value: []string{"foo", "bar"}}}) // user object
+
+	// is_callable
+	expect(t, `out = is_callable(1)`, false)
+	expect(t, `out = is_callable(func() {})`, true)
+	expect(t, `out = is_callable(func(x) { return x })`, true)
+	expect(t, `out = is_callable(len)`, true)                                                                 // builtin function
+	expect(t, `a := func(x) { return func() { return x } }; out = is_callable(a)`, true)                      // function
+	expect(t, `a := func(x) { return func() { return x } }; out = is_callable(a(5))`, true)                   // closure
+	expectWithSymbols(t, `out = is_callable(x)`, true, SYM{"x": &StringArray{Value: []string{"foo", "bar"}}}) // user object
+
 }