diff --git a/docs/builtins.md b/docs/builtins.md
index 38d4252..6cd0003 100644
--- a/docs/builtins.md
+++ b/docs/builtins.md
@@ -195,6 +195,10 @@ Returns `true` if the object's type is map. Or it returns `false`.
 
 Returns `true` if the object's type is immutable map. Or it returns `false`.
 
+## is_iterable
+
+Returns `true` if the object's type is iterable: array, immutable array, map, immutable map, string, and bytes are iterable types in Tengo.
+
 ## is_time
 
 Returns `true` if the object's type is time. Or it returns `false`.
diff --git a/docs/runtime-types.md b/docs/runtime-types.md
index eb1e6a9..e5779f1 100644
--- a/docs/runtime-types.md
+++ b/docs/runtime-types.md
@@ -61,6 +61,7 @@ _* time.Unix(): use `time.Unix(v, 0)` to convert to Time_
 - `bytes(x)`: tries to convert `x` into bytes; returns `undefined` if failed
   - `bytes(N)`: as a special case this will create a Bytes variable with the given size `N` (only if `N` is int)
 - `time(x)`: tries to convert `x` into time; returns `undefined` if failed
+- See [Builtins](https://github.com/d5/tengo/blob/master/docs/builtins.md) for the full list of builtin functions.
 
 ## Type Checking Builtin Functions
 
@@ -76,4 +77,5 @@ _* time.Unix(): use `time.Unix(v, 0)` to convert to Time_
 - `is_immutable_map(x)`: return `true` if `x` is immutable map; `false` otherwise
 - `is_time(x)`: return `true` if `x` is time; `false` otherwise
 - `is_error(x)`: returns `true` if `x` is error; `false` otherwise
-- `is_undefined(x)`: returns `true` if `x` is undefined; `false` otherwise
\ No newline at end of file
+- `is_undefined(x)`: returns `true` if `x` is undefined; `false` otherwise
+- See [Builtins](https://github.com/d5/tengo/blob/master/docs/builtins.md) for the full list of builtin functions.
\ No newline at end of file
diff --git a/docs/stdlib-enum.md b/docs/stdlib-enum.md
new file mode 100644
index 0000000..033e898
--- /dev/null
+++ b/docs/stdlib-enum.md
@@ -0,0 +1,19 @@
+# Module - "enum"
+
+```golang
+enum := import("enum")
+```
+
+## Functions
+
+- `all(x, fn) => bool`: returns true if the given function `fn` evaluates to a truthy value on all of the items in `x`. It returns undefined if `x` is not enumerable.
+- `any(x, fn) => bool`: returns true if the given function `fn` evaluates to a truthy value on any of the items in `x`. It returns undefined if `x` is not enumerable.
+- `chunk(x, size) => [object]`: returns an array of elements split into groups the length of size. If `x` can't be split evenly, the final chunk will be the remaining elements. It returns undefined if `x` is not array.
+- `at(x, key) => object`: returns an element at the given index (if `x` is array) or key (if `x` is map). It returns undefined if `x` is not enumerable.
+- `each(x, fn)`: iterates over elements of `x` and invokes `fn` for each element. `fn` is invoked with two arguments: `key` and `value`. `key` is an int index if `x` is array. `key` is a string key if `x` is map. It does not iterate and returns undefined if `x` is not enumerable.`
+- `filter(x, fn) => [object]`: iterates over elements of `x`, returning an array of all elements `fn` returns truthy for. `fn` is invoked with two arguments: `key` and `value`. `key` is an int index if `x` is array. `key` is a string key if `x` is map. It returns undefined if `x` is not enumerable.
+- `find(x, fn) => object`: iterates over elements of `x`, returning value of the first element `fn` returns truthy for. `fn` is invoked with two arguments: `key` and `value`. `key` is an int index if `x` is array. `key` is a string key if `x` is map. It returns undefined if `x` is not enumerable.
+- `find_key(x, fn) => int/string`: iterates over elements of `x`, returning key or index of the first element `fn` returns truthy for. `fn` is invoked with two arguments: `key` and `value`. `key` is an int index if `x` is array. `key` is a string key if `x` is map. It returns undefined if `x` is not enumerable.
+- `map(x, fn) => [object]`: creates an array of values by running each element in `x` through `fn`. `fn` is invoked with two arguments: `key` and `value`. `key` is an int index if `x` is array. `key` is a string key if `x` is map. It returns undefined if `x` is not enumerable.
+- `key(k, _) => object`: returns the first argument.
+- `value(_, v) => object`: returns the second argument.
\ No newline at end of file
diff --git a/docs/stdlib.md b/docs/stdlib.md
index e051f75..ccb4f1c 100644
--- a/docs/stdlib.md
+++ b/docs/stdlib.md
@@ -6,4 +6,5 @@
 - [times](https://github.com/d5/tengo/blob/master/docs/stdlib-times.md): time-related functions
 - [rand](https://github.com/d5/tengo/blob/master/docs/stdlib-rand.md): random functions
 - [fmt](https://github.com/d5/tengo/blob/master/docs/stdlib-fmt.md): formatting functions
-- [json](https://github.com/d5/tengo/blob/master/docs/stdlib-json.md): JSON functions
\ No newline at end of file
+- [json](https://github.com/d5/tengo/blob/master/docs/stdlib-json.md): JSON functions
+- [enum](https://github.com/d5/tengo/blob/master/docs/stdlib-enum.md): Enumeration functions
\ No newline at end of file
diff --git a/objects/builtin_type_checks.go b/objects/builtin_type_checks.go
index 960f782..d1e8471 100644
--- a/objects/builtin_type_checks.go
+++ b/objects/builtin_type_checks.go
@@ -181,3 +181,15 @@ func builtinIsCallable(args ...Object) (Object, error) {
 
 	return FalseValue, nil
 }
+
+func builtinIsIterable(args ...Object) (Object, error) {
+	if len(args) != 1 {
+		return nil, ErrWrongNumArguments
+	}
+
+	if _, ok := args[0].(Iterable); ok {
+		return TrueValue, nil
+	}
+
+	return FalseValue, nil
+}
diff --git a/objects/builtins.go b/objects/builtins.go
index 67aec46..bfd004d 100644
--- a/objects/builtins.go
+++ b/objects/builtins.go
@@ -83,6 +83,10 @@ var Builtins = []*BuiltinFunction{
 		Name:  "is_immutable_map",
 		Value: builtinIsImmutableMap,
 	},
+	{
+		Name:  "is_iterable",
+		Value: builtinIsIterable,
+	},
 	{
 		Name:  "is_time",
 		Value: builtinIsTime,
diff --git a/objects/bytes.go b/objects/bytes.go
index 16b6168..6710c7c 100644
--- a/objects/bytes.go
+++ b/objects/bytes.go
@@ -79,3 +79,11 @@ func (o *Bytes) IndexGet(index Object) (res Object, err error) {
 
 	return
 }
+
+// Iterate creates a bytes iterator.
+func (o *Bytes) Iterate() Iterator {
+	return &BytesIterator{
+		v: o.Value,
+		l: len(o.Value),
+	}
+}
diff --git a/objects/bytes_iterator.go b/objects/bytes_iterator.go
new file mode 100644
index 0000000..18a36e1
--- /dev/null
+++ b/objects/bytes_iterator.go
@@ -0,0 +1,57 @@
+package objects
+
+import "github.com/d5/tengo/compiler/token"
+
+// BytesIterator represents an iterator for a string.
+type BytesIterator struct {
+	v []byte
+	i int
+	l int
+}
+
+// TypeName returns the name of the type.
+func (i *BytesIterator) TypeName() string {
+	return "bytes-iterator"
+}
+
+func (i *BytesIterator) String() string {
+	return "<bytes-iterator>"
+}
+
+// BinaryOp returns another object that is the result of
+// a given binary operator and a right-hand side object.
+func (i *BytesIterator) BinaryOp(op token.Token, rhs Object) (Object, error) {
+	return nil, ErrInvalidOperator
+}
+
+// IsFalsy returns true if the value of the type is falsy.
+func (i *BytesIterator) IsFalsy() bool {
+	return true
+}
+
+// Equals returns true if the value of the type
+// is equal to the value of another object.
+func (i *BytesIterator) Equals(Object) bool {
+	return false
+}
+
+// Copy returns a copy of the type.
+func (i *BytesIterator) Copy() Object {
+	return &BytesIterator{v: i.v, i: i.i, l: i.l}
+}
+
+// Next returns true if there are more elements to iterate.
+func (i *BytesIterator) Next() bool {
+	i.i++
+	return i.i <= i.l
+}
+
+// Key returns the key or index value of the current element.
+func (i *BytesIterator) Key() Object {
+	return &Int{Value: int64(i.i - 1)}
+}
+
+// Value returns the value of the current element.
+func (i *BytesIterator) Value() Object {
+	return &Int{Value: int64(i.v[i.i-1])}
+}
diff --git a/objects/module_map.go b/objects/module_map.go
index 7b4d3bb..874b8a2 100644
--- a/objects/module_map.go
+++ b/objects/module_map.go
@@ -68,3 +68,10 @@ func (m *ModuleMap) Copy() *ModuleMap {
 func (m *ModuleMap) Len() int {
 	return len(m.m)
 }
+
+// AddMap adds named modules from another module map.
+func (m *ModuleMap) AddMap(o *ModuleMap) {
+	for name, mod := range o.m {
+		m.m[name] = mod
+	}
+}
diff --git a/runtime/vm_source_modules_test.go b/runtime/vm_source_modules_test.go
index ab5ca3a..660170c 100644
--- a/runtime/vm_source_modules_test.go
+++ b/runtime/vm_source_modules_test.go
@@ -3,11 +3,140 @@ package runtime_test
 import (
 	"testing"
 
+	"github.com/d5/tengo/objects"
 	"github.com/d5/tengo/stdlib"
 )
 
 func TestSourceModules(t *testing.T) {
-	expect(t, `enum := import("enum"); out = enum.any([1,2,3], func(i, v) { return v == 2 })`,
-		Opts().Module("enum", stdlib.SourceModules["enum"]),
-		true)
+	testEnumModule(t, `out = enum.key(0, 20)`, 0)
+	testEnumModule(t, `out = enum.key(10, 20)`, 10)
+	testEnumModule(t, `out = enum.value(0, 0)`, 0)
+	testEnumModule(t, `out = enum.value(10, 20)`, 20)
+
+	testEnumModule(t, `out = enum.all([], enum.value)`, true)
+	testEnumModule(t, `out = enum.all([1], enum.value)`, true)
+	testEnumModule(t, `out = enum.all([true, 1], enum.value)`, true)
+	testEnumModule(t, `out = enum.all([true, 0], enum.value)`, false)
+	testEnumModule(t, `out = enum.all([true, 0, 1], enum.value)`, false)
+	testEnumModule(t, `out = enum.all(immutable([true, 0, 1]), enum.value)`, false) // immutable-array
+	testEnumModule(t, `out = enum.all({}, enum.value)`, true)
+	testEnumModule(t, `out = enum.all({a:1}, enum.value)`, true)
+	testEnumModule(t, `out = enum.all({a:true, b:1}, enum.value)`, true)
+	testEnumModule(t, `out = enum.all(immutable({a:true, b:1}), enum.value)`, true) // immutable-map
+	testEnumModule(t, `out = enum.all({a:true, b:0}, enum.value)`, false)
+	testEnumModule(t, `out = enum.all({a:true, b:0, c:1}, enum.value)`, false)
+	testEnumModule(t, `out = enum.all(0, enum.value)`, objects.UndefinedValue)     // non-enumerable: undefined
+	testEnumModule(t, `out = enum.all("123", enum.value)`, objects.UndefinedValue) // non-enumerable: undefined
+
+	testEnumModule(t, `out = enum.any([], enum.value)`, false)
+	testEnumModule(t, `out = enum.any([1], enum.value)`, true)
+	testEnumModule(t, `out = enum.any([true, 1], enum.value)`, true)
+	testEnumModule(t, `out = enum.any([true, 0], enum.value)`, true)
+	testEnumModule(t, `out = enum.any([true, 0, 1], enum.value)`, true)
+	testEnumModule(t, `out = enum.any(immutable([true, 0, 1]), enum.value)`, true) // immutable-array
+	testEnumModule(t, `out = enum.any([false], enum.value)`, false)
+	testEnumModule(t, `out = enum.any([false, 0], enum.value)`, false)
+	testEnumModule(t, `out = enum.any({}, enum.value)`, false)
+	testEnumModule(t, `out = enum.any({a:1}, enum.value)`, true)
+	testEnumModule(t, `out = enum.any({a:true, b:1}, enum.value)`, true)
+	testEnumModule(t, `out = enum.any({a:true, b:0}, enum.value)`, true)
+	testEnumModule(t, `out = enum.any({a:true, b:0, c:1}, enum.value)`, true)
+	testEnumModule(t, `out = enum.any(immutable({a:true, b:0, c:1}), enum.value)`, true) // immutable-map
+	testEnumModule(t, `out = enum.any({a:false}, enum.value)`, false)
+	testEnumModule(t, `out = enum.any({a:false, b:0}, enum.value)`, false)
+	testEnumModule(t, `out = enum.any(0, enum.value)`, objects.UndefinedValue)     // non-enumerable: undefined
+	testEnumModule(t, `out = enum.any("123", enum.value)`, objects.UndefinedValue) // non-enumerable: undefined
+
+	testEnumModule(t, `out = enum.chunk([], 1)`, ARR{})
+	testEnumModule(t, `out = enum.chunk([1], 1)`, ARR{ARR{1}})
+	testEnumModule(t, `out = enum.chunk([1,2,3], 1)`, ARR{ARR{1}, ARR{2}, ARR{3}})
+	testEnumModule(t, `out = enum.chunk([1,2,3], 2)`, ARR{ARR{1, 2}, ARR{3}})
+	testEnumModule(t, `out = enum.chunk([1,2,3], 3)`, ARR{ARR{1, 2, 3}})
+	testEnumModule(t, `out = enum.chunk([1,2,3], 4)`, ARR{ARR{1, 2, 3}})
+	testEnumModule(t, `out = enum.chunk([1,2,3,4], 3)`, ARR{ARR{1, 2, 3}, ARR{4}})
+	testEnumModule(t, `out = enum.chunk([], 0)`, objects.UndefinedValue)            // size=0: undefined
+	testEnumModule(t, `out = enum.chunk([1], 0)`, objects.UndefinedValue)           // size=0: undefined
+	testEnumModule(t, `out = enum.chunk([1,2,3], 0)`, objects.UndefinedValue)       // size=0: undefined
+	testEnumModule(t, `out = enum.chunk({a:1,b:2,c:3}, 1)`, objects.UndefinedValue) // map: undefined
+	testEnumModule(t, `out = enum.chunk(0, 1)`, objects.UndefinedValue)             // non-enumerable: undefined
+	testEnumModule(t, `out = enum.chunk("123", 1)`, objects.UndefinedValue)         // non-enumerable: undefined
+
+	testEnumModule(t, `out = enum.at([], 0)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at([], 1)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at([], -1)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at(["one"], 0)`, "one")
+	testEnumModule(t, `out = enum.at(["one"], 1)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at(["one"], -1)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at(["one","two","three"], 0)`, "one")
+	testEnumModule(t, `out = enum.at(["one","two","three"], 1)`, "two")
+	testEnumModule(t, `out = enum.at(["one","two","three"], 2)`, "three")
+	testEnumModule(t, `out = enum.at(["one","two","three"], -1)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at(["one","two","three"], 3)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at(["one","two","three"], "1")`, objects.UndefinedValue) // non-int index: undefined
+	testEnumModule(t, `out = enum.at({}, "a")`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at({a:"one"}, "a")`, "one")
+	testEnumModule(t, `out = enum.at({a:"one"}, "b")`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at({a:"one",b:"two",c:"three"}, "a")`, "one")
+	testEnumModule(t, `out = enum.at({a:"one",b:"two",c:"three"}, "b")`, "two")
+	testEnumModule(t, `out = enum.at({a:"one",b:"two",c:"three"}, "c")`, "three")
+	testEnumModule(t, `out = enum.at({a:"one",b:"two",c:"three"}, "d")`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.at({a:"one",b:"two",c:"three"}, 'a')`, objects.UndefinedValue) // non-string index: undefined
+	testEnumModule(t, `out = enum.at(0, 1)`, objects.UndefinedValue)                             // non-enumerable: undefined
+	testEnumModule(t, `out = enum.at("abc", 1)`, objects.UndefinedValue)                         // non-enumerable: undefined
+
+	testEnumModule(t, `out=0; enum.each([],func(k,v){out+=v})`, 0)
+	testEnumModule(t, `out=0; enum.each([1,2,3],func(k,v){out+=v})`, 6)
+	testEnumModule(t, `out=0; enum.each([1,2,3],func(k,v){out+=k})`, 3)
+	testEnumModule(t, `out=0; enum.each({a:1,b:2,c:3},func(k,v){out+=v})`, 6)
+	testEnumModule(t, `out=""; enum.each({a:1,b:2,c:3},func(k,v){out+=k}); out=len(out)`, 3)
+	testEnumModule(t, `out=0; enum.each(5,func(k,v){out+=v})`, 0)     // non-enumerable: no iteration
+	testEnumModule(t, `out=0; enum.each("123",func(k,v){out+=v})`, 0) // non-enumerable: no iteration
+
+	testEnumModule(t, `out = enum.filter([], enum.value)`, ARR{})
+	testEnumModule(t, `out = enum.filter([false,1,2], enum.value)`, ARR{1, 2})
+	testEnumModule(t, `out = enum.filter([false,1,0,2], enum.value)`, ARR{1, 2})
+	testEnumModule(t, `out = enum.filter({}, enum.value)`, objects.UndefinedValue)    // non-array: undefined
+	testEnumModule(t, `out = enum.filter(0, enum.value)`, objects.UndefinedValue)     // non-array: undefined
+	testEnumModule(t, `out = enum.filter("123", enum.value)`, objects.UndefinedValue) // non-array: undefined
+
+	testEnumModule(t, `out = enum.find([], enum.value)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.find([0], enum.value)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.find([1], enum.value)`, 1)
+	testEnumModule(t, `out = enum.find([false,0,undefined,1], enum.value)`, 1)
+	testEnumModule(t, `out = enum.find([1,2,3], enum.value)`, 1)
+	testEnumModule(t, `out = enum.find({}, enum.value)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.find({a:0}, enum.value)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.find({a:1}, enum.value)`, 1)
+	testEnumModule(t, `out = enum.find({a:false,b:0,c:undefined,d:1}, enum.value)`, 1)
+	//testEnumModule(t, `out = enum.find({a:1,b:2,c:3}, enum.value)`, 1)
+	testEnumModule(t, `out = enum.find(0, enum.value)`, objects.UndefinedValue)     // non-enumerable: undefined
+	testEnumModule(t, `out = enum.find("123", enum.value)`, objects.UndefinedValue) // non-enumerable: undefined
+
+	testEnumModule(t, `out = enum.find_key([], enum.value)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.find_key([0], enum.value)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.find_key([1], enum.value)`, 0)
+	testEnumModule(t, `out = enum.find_key([false,0,undefined,1], enum.value)`, 3)
+	testEnumModule(t, `out = enum.find_key([1,2,3], enum.value)`, 0)
+	testEnumModule(t, `out = enum.find_key({}, enum.value)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.find_key({a:0}, enum.value)`, objects.UndefinedValue)
+	testEnumModule(t, `out = enum.find_key({a:1}, enum.value)`, "a")
+	testEnumModule(t, `out = enum.find_key({a:false,b:0,c:undefined,d:1}, enum.value)`, "d")
+	//testEnumModule(t, `out = enum.find_key({a:1,b:2,c:3}, enum.value)`, "a")
+	testEnumModule(t, `out = enum.find_key(0, enum.value)`, objects.UndefinedValue)     // non-enumerable: undefined
+	testEnumModule(t, `out = enum.find_key("123", enum.value)`, objects.UndefinedValue) // non-enumerable: undefined
+
+	testEnumModule(t, `out = enum.map([], enum.value)`, ARR{})
+	testEnumModule(t, `out = enum.map([1,2,3], enum.value)`, ARR{1, 2, 3})
+	testEnumModule(t, `out = enum.map([1,2,3], enum.key)`, ARR{0, 1, 2})
+	testEnumModule(t, `out = enum.map([1,2,3], func(k,v) { return v*2 })`, ARR{2, 4, 6})
+	testEnumModule(t, `out = enum.map({}, enum.value)`, ARR{})
+	testEnumModule(t, `out = enum.map({a:1}, func(k,v) { return v*2 })`, ARR{2})
+	testEnumModule(t, `out = enum.map(0, enum.value)`, objects.UndefinedValue)     // non-enumerable: undefined
+	testEnumModule(t, `out = enum.map("123", enum.value)`, objects.UndefinedValue) // non-enumerable: undefined
+}
+
+func testEnumModule(t *testing.T, input string, expected interface{}) {
+	expect(t, `enum := import("enum"); `+input,
+		Opts().Module("enum", stdlib.SourceModules["enum"]),
+		expected)
 }
diff --git a/runtime/vm_srcmod_test.go b/runtime/vm_srcmod_test.go
new file mode 100644
index 0000000..e7a0f6f
--- /dev/null
+++ b/runtime/vm_srcmod_test.go
@@ -0,0 +1,49 @@
+package runtime_test
+
+import "testing"
+
+func TestSrcModEnum(t *testing.T) {
+	expect(t, `
+x := import("enum")
+out = x.all([1, 2, 3], func(_, v) { return v >= 1 }) 
+`, Opts().Stdlib(), true)
+	expect(t, `
+x := import("enum")
+out = x.all([1, 2, 3], func(_, v) { return v >= 2 }) 
+`, Opts().Stdlib(), false)
+
+	expect(t, `
+x := import("enum")
+out = x.any([1, 2, 3], func(_, v) { return v >= 1 }) 
+`, Opts().Stdlib(), true)
+	expect(t, `
+x := import("enum")
+out = x.any([1, 2, 3], func(_, v) { return v >= 2 }) 
+`, Opts().Stdlib(), true)
+
+	expect(t, `
+x := import("enum")
+out = x.chunk([1, 2, 3], 1) 
+`, Opts().Stdlib(), ARR{ARR{1}, ARR{2}, ARR{3}})
+	expect(t, `
+x := import("enum")
+out = x.chunk([1, 2, 3], 2) 
+`, Opts().Stdlib(), ARR{ARR{1, 2}, ARR{3}})
+	expect(t, `
+x := import("enum")
+out = x.chunk([1, 2, 3], 3) 
+`, Opts().Stdlib(), ARR{ARR{1, 2, 3}})
+	expect(t, `
+x := import("enum")
+out = x.chunk([1, 2, 3], 4) 
+`, Opts().Stdlib(), ARR{ARR{1, 2, 3}})
+	expect(t, `
+x := import("enum")
+out = x.chunk([1, 2, 3, 4, 5, 6], 2) 
+`, Opts().Stdlib(), ARR{ARR{1, 2}, ARR{3, 4}, ARR{5, 6}})
+
+	expect(t, `
+x := import("enum")
+out = x.at([1, 2, 3], 0) 
+`, Opts().Stdlib(), 1)
+}
diff --git a/runtime/vm_test.go b/runtime/vm_test.go
index ed56ac3..152b9e7 100644
--- a/runtime/vm_test.go
+++ b/runtime/vm_test.go
@@ -14,6 +14,7 @@ import (
 	"github.com/d5/tengo/compiler/source"
 	"github.com/d5/tengo/objects"
 	"github.com/d5/tengo/runtime"
+	"github.com/d5/tengo/stdlib"
 )
 
 const testOut = "out"
@@ -52,6 +53,11 @@ func (o *testopts) copy() *testopts {
 	return c
 }
 
+func (o *testopts) Stdlib() *testopts {
+	o.modules.AddMap(stdlib.GetModuleMap(stdlib.AllModuleNames()...))
+	return o
+}
+
 func (o *testopts) Module(name string, mod interface{}) *testopts {
 	c := o.copy()
 	switch mod := mod.(type) {
diff --git a/stdlib/enum_test.go b/stdlib/enum_test.go
deleted file mode 100644
index 393399f..0000000
--- a/stdlib/enum_test.go
+++ /dev/null
@@ -1,7 +0,0 @@
-package stdlib_test
-
-import "testing"
-
-func TestEnum(t *testing.T) {
-
-}
diff --git a/stdlib/gensrcmods.go b/stdlib/gensrcmods.go
index e048e00..fada66b 100644
--- a/stdlib/gensrcmods.go
+++ b/stdlib/gensrcmods.go
@@ -7,6 +7,7 @@ import (
 	"io/ioutil"
 	"log"
 	"regexp"
+	"strconv"
 )
 
 var tengoModFileRE = regexp.MustCompile(`^srcmod_(\w+).tengo$`)
@@ -41,7 +42,7 @@ package stdlib
 // SourceModules are source type standard library modules.
 var SourceModules = map[string]string{` + "\n")
 	for modName, modSrc := range modules {
-		out.WriteString("\t\"" + modName + "\": `" + modSrc + "`,\n")
+		out.WriteString("\t\"" + modName + "\": " + strconv.Quote(modSrc) + ",\n")
 	}
 	out.WriteString("}\n")
 
diff --git a/stdlib/source_modules.go b/stdlib/source_modules.go
index cadc87c..ca69d7d 100644
--- a/stdlib/source_modules.go
+++ b/stdlib/source_modules.go
@@ -4,45 +4,5 @@ package stdlib
 
 // SourceModules are source type standard library modules.
 var SourceModules = map[string]string{
-	"enum": `export {
-  // all returns true if the given function fn evaluates to a truthy value on
-  // all of the items in the enumerable.
-  all: func(enumerable, fn) {
-    for k, v in enumerable {
-      if !fn(k, v) {
-        return false
-      }
-    }
-    return true
-  },
-  // any returns true if the given function fn evaluates to a truthy value on
-  // any of the items in the enumerable.
-  any: func(enumerable, fn) {
-    for k, v in enumerable {
-      if fn(k, v) {
-        return true
-      }
-    }
-    return false
-  },
-  // chunk returns an array of elements split into groups the length of size.
-  // If the enumerable can't be split evenly, the final chunk will be the
-  // remaining elements.
-  chunk: func(enumerable, size) {
-    numElements := len(enumerable)
-
-    if !numElements {
-      return []
-    }
-    
-    res := []
-    idx := 0
-    for idx < numElements {
-      res = append(res, enumerable[idx:idx+size])
-      idx += size
-    }
-    return res
-  }
-}
-`,
+	"enum": "is_enumerable := func(x) {\n  return is_array(x) || is_map(x) || is_immutable_array(x) || is_immutable_map(x)\n}\n\nis_array_like := func(x) {\n  return is_array(x) || is_immutable_array(x)\n}\n\nexport {\n  // all returns true if the given function `fn` evaluates to a truthy value on\n  // all of the items in `x`. It returns undefined if `x` is not enumerable.\n  all: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      if !fn(k, v) { return false }\n    }\n\n    return true\n  },\n  // any returns true if the given function `fn` evaluates to a truthy value on\n  // any of the items in `x`. It returns undefined if `x` is not enumerable.\n  any: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      if fn(k, v) { return true }\n    }\n\n    return false\n  },\n  // chunk returns an array of elements split into groups the length of size.\n  // If `x` can't be split evenly, the final chunk will be the remaining elements.\n  // It returns undefined if `x` is not array.\n  chunk: func(x, size) {\n    if !is_array_like(x) || !size { return undefined }\n\n    numElements := len(x)\n    if !numElements { return [] }\n\n    res := []\n    idx := 0\n    for idx < numElements {\n      res = append(res, x[idx:idx+size])\n      idx += size\n    }\n\n    return res\n  },\n  // at returns an element at the given index (if `x` is array) or\n  // key (if `x` is map). It returns undefined if `x` is not enumerable.\n  at: func(x, key) {\n    if !is_enumerable(x) { return undefined }\n\n    if is_array_like(x) {\n        if !is_int(key) { return undefined }\n    } else {\n        if !is_string(key) { return undefined }\n    }\n\n    return x[key]\n  },\n  // each iterates over elements of `x` and invokes `fn` for each element. `fn` is\n  // invoked with two arguments: `key` and `value`. `key` is an int index\n  // if `x` is array. `key` is a string key if `x` is map. It does not iterate\n  // and returns undefined if `x` is not enumerable.\n  each: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      fn(k, v)\n    }\n  },\n  // filter iterates over elements of `x`, returning an array of all elements `fn`\n  // returns truthy for. `fn` is invoked with two arguments: `key` and `value`.\n  // `key` is an int index if `x` is array. `key` is a string key if `x` is map.\n  // It returns undefined if `x` is not enumerable.\n  filter: func(x, fn) {\n    if !is_array_like(x) { return undefined }\n\n    dst := []\n    for k, v in x {\n      if fn(k, v) { dst = append(dst, v) }\n    }\n\n    return dst\n  },\n  // find iterates over elements of `x`, returning value of the first element `fn`\n  // returns truthy for. `fn` is invoked with two arguments: `key` and `value`.\n  // `key` is an int index if `x` is array. `key` is a string key if `x` is map.\n  // It returns undefined if `x` is not enumerable.\n  find: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      if fn(k, v) { return v }\n    }\n  },\n  // find_key iterates over elements of `x`, returning key or index of the first\n  // element `fn` returns truthy for. `fn` is invoked with two arguments: `key`\n  // and `value`. `key` is an int index if `x` is array. `key` is a string key if\n  // `x` is map. It returns undefined if `x` is not enumerable.\n  find_key: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    for k, v in x {\n      if fn(k, v) { return k }\n    }\n  },\n  // map creates an array of values by running each element in `x` through `fn`.\n  // `fn` is invoked with two arguments: `key` and `value`. `key` is an int index\n  // if `x` is array. `key` is a string key if `x` is map. It returns undefined\n  // if `x` is not enumerable.\n  map: func(x, fn) {\n    if !is_enumerable(x) { return undefined }\n\n    dst := []\n    for k, v in x {\n      dst = append(dst, fn(k, v))\n    }\n\n    return dst\n  },\n  // key returns the first argument.\n  key: func(k, _) { return k },\n  // value returns the second argument.\n  value: func(_, v) { return v }\n}\n",
 }
diff --git a/stdlib/srcmod_enum.tengo b/stdlib/srcmod_enum.tengo
index 914d78a..7a5ea63 100644
--- a/stdlib/srcmod_enum.tengo
+++ b/stdlib/srcmod_enum.tengo
@@ -1,40 +1,128 @@
+is_enumerable := func(x) {
+  return is_array(x) || is_map(x) || is_immutable_array(x) || is_immutable_map(x)
+}
+
+is_array_like := func(x) {
+  return is_array(x) || is_immutable_array(x)
+}
+
 export {
-  // all returns true if the given function fn evaluates to a truthy value on
-  // all of the items in the enumerable.
-  all: func(enumerable, fn) {
-    for k, v in enumerable {
-      if !fn(k, v) {
-        return false
-      }
+  // all returns true if the given function `fn` evaluates to a truthy value on
+  // all of the items in `x`. It returns undefined if `x` is not enumerable.
+  all: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      if !fn(k, v) { return false }
     }
+
     return true
   },
-  // any returns true if the given function fn evaluates to a truthy value on
-  // any of the items in the enumerable.
-  any: func(enumerable, fn) {
-    for k, v in enumerable {
-      if fn(k, v) {
-        return true
-      }
+  // any returns true if the given function `fn` evaluates to a truthy value on
+  // any of the items in `x`. It returns undefined if `x` is not enumerable.
+  any: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      if fn(k, v) { return true }
     }
+
     return false
   },
   // chunk returns an array of elements split into groups the length of size.
-  // If the enumerable can't be split evenly, the final chunk will be the
-  // remaining elements.
-  chunk: func(enumerable, size) {
-    numElements := len(enumerable)
+  // If `x` can't be split evenly, the final chunk will be the remaining elements.
+  // It returns undefined if `x` is not array.
+  chunk: func(x, size) {
+    if !is_array_like(x) || !size { return undefined }
+
+    numElements := len(x)
+    if !numElements { return [] }
 
-    if !numElements {
-      return []
-    }
-    
     res := []
     idx := 0
     for idx < numElements {
-      res = append(res, enumerable[idx:idx+size])
+      res = append(res, x[idx:idx+size])
       idx += size
     }
+
     return res
-  }
+  },
+  // at returns an element at the given index (if `x` is array) or
+  // key (if `x` is map). It returns undefined if `x` is not enumerable.
+  at: func(x, key) {
+    if !is_enumerable(x) { return undefined }
+
+    if is_array_like(x) {
+        if !is_int(key) { return undefined }
+    } else {
+        if !is_string(key) { return undefined }
+    }
+
+    return x[key]
+  },
+  // each iterates over elements of `x` and invokes `fn` for each element. `fn` is
+  // invoked with two arguments: `key` and `value`. `key` is an int index
+  // if `x` is array. `key` is a string key if `x` is map. It does not iterate
+  // and returns undefined if `x` is not enumerable.
+  each: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      fn(k, v)
+    }
+  },
+  // filter iterates over elements of `x`, returning an array of all elements `fn`
+  // returns truthy for. `fn` is invoked with two arguments: `key` and `value`.
+  // `key` is an int index if `x` is array. `key` is a string key if `x` is map.
+  // It returns undefined if `x` is not enumerable.
+  filter: func(x, fn) {
+    if !is_array_like(x) { return undefined }
+
+    dst := []
+    for k, v in x {
+      if fn(k, v) { dst = append(dst, v) }
+    }
+
+    return dst
+  },
+  // find iterates over elements of `x`, returning value of the first element `fn`
+  // returns truthy for. `fn` is invoked with two arguments: `key` and `value`.
+  // `key` is an int index if `x` is array. `key` is a string key if `x` is map.
+  // It returns undefined if `x` is not enumerable.
+  find: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      if fn(k, v) { return v }
+    }
+  },
+  // find_key iterates over elements of `x`, returning key or index of the first
+  // element `fn` returns truthy for. `fn` is invoked with two arguments: `key`
+  // and `value`. `key` is an int index if `x` is array. `key` is a string key if
+  // `x` is map. It returns undefined if `x` is not enumerable.
+  find_key: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    for k, v in x {
+      if fn(k, v) { return k }
+    }
+  },
+  // map creates an array of values by running each element in `x` through `fn`.
+  // `fn` is invoked with two arguments: `key` and `value`. `key` is an int index
+  // if `x` is array. `key` is a string key if `x` is map. It returns undefined
+  // if `x` is not enumerable.
+  map: func(x, fn) {
+    if !is_enumerable(x) { return undefined }
+
+    dst := []
+    for k, v in x {
+      dst = append(dst, fn(k, v))
+    }
+
+    return dst
+  },
+  // key returns the first argument.
+  key: func(k, _) { return k },
+  // value returns the second argument.
+  value: func(_, v) { return v }
 }