diff --git a/core/global.d.ts b/core/global.d.ts
index 23efda4..fe56b5d 100644
--- a/core/global.d.ts
+++ b/core/global.d.ts
@@ -25,7 +25,11 @@ declare const _G: typeof globalThis;
  * otherwise, returns all its arguments. In case of error, `message` is the
  * error object; when absent, it defaults to "assertion failed!"
  */
-declare function assert(v: any, message?: string): asserts v;
+declare function assert<V>(v: V): Exclude<V, undefined | null | false>;
+declare function assert<V, A extends any[]>(
+    v: V,
+    ...args: A
+): LuaMultiReturn<[Exclude<V, undefined | null | false>, ...A]>;
 
 /**
  * This function is a generic interface to the garbage collector. It performs
@@ -109,7 +113,7 @@ declare function error(message: string, level?: number): never;
  * metatable has a __metatable field, returns the associated value. Otherwise,
  * returns the metatable of the given object.
  */
-declare function getmetatable<T extends object>(object: T): LuaMetatable<T> | undefined;
+declare function getmetatable<T>(object: T): LuaMetatable<T> | undefined;
 
 /**
  * Returns three values (an iterator function, the table t, and 0) so that the
@@ -153,6 +157,9 @@ declare function next(table: object, index?: any): LuaMultiReturn<[any, any] | [
  * See function next for the caveats of modifying the table during its
  * traversal.
  */
+declare function pairs<TKey, TValue>(
+    t: LuaTable<TKey, TValue>
+): LuaIterable<LuaMultiReturn<[TKey, TValue]>>;
 declare function pairs<T>(t: T): LuaIterable<LuaMultiReturn<[keyof T, T[keyof T]]>>;
 
 /**
@@ -234,10 +241,17 @@ declare function select<T>(index: '#', ...args: T[]): number;
  *
  * This function returns table.
  */
-declare function setmetatable<T extends object, TIndex extends object>(
+declare function setmetatable<
+    T extends object,
+    TIndex extends object | ((this: T, key: any) => any) | undefined = undefined
+>(
     table: T,
-    metatable: LuaMetatable<T & TIndex, TIndex> | null | undefined
-): T & TIndex;
+    metatable?: LuaMetatable<T, TIndex> | null
+): TIndex extends (this: T, key: infer TKey) => infer TValue
+    ? T & { [K in TKey & string]: TValue }
+    : TIndex extends object
+    ? T & TIndex
+    : T;
 
 /**
  * When called with no base, tonumber tries to convert its argument to a number.
diff --git a/core/io.d.ts b/core/io.d.ts
index 9edabba..9c35097 100644
--- a/core/io.d.ts
+++ b/core/io.d.ts
@@ -61,9 +61,7 @@ declare namespace io {
         filename?: string,
         ...formats: T
     ): LuaIterable<
-        LuaMultiReturn<
-            [] extends T ? [string] : { [P in keyof T]: T[P] extends 'n' ? number : string }
-        >
+        LuaMultiReturn<[] extends T ? [string] : { [P in keyof T]: FileReadFormatToType<T[P]> }>
     >;
 
     /**
@@ -100,12 +98,31 @@ declare namespace io {
      * you can use to read data from this program (if mode is "r", the default) or
      * to write data to this program (if mode is "w").
      */
-    function popen(prog: string, mode?: 'r' | 'w'): LuaFile;
+    function popen(prog: string, mode?: 'r' | 'w'): LuaMultiReturn<[LuaFile] | [undefined, string]>;
 
     /**
      * Equivalent to io.input():read(···).
      */
-    const read: LuaFile['read'];
+    function read(): io.FileReadFormatToType<io.FileReadLineFormat> | undefined;
+    function read<T extends io.FileReadFormat>(format: T): io.FileReadFormatToType<T> | undefined;
+    function read<T extends io.FileReadFormat[]>(
+        ...formats: T
+    ): LuaMultiReturn<{ [P in keyof T]?: io.FileReadFormatToType<T[P]> }>;
+
+    /**
+     * Predefined file handle for standard error stream. The I/O library never closes this file.
+     */
+    const stderr: LuaFile;
+
+    /**
+     * Predefined file handle for standard input stream. The I/O library never closes this file.
+     */
+    const stdin: LuaFile;
+
+    /**
+     * Predefined file handle for standard output stream. The I/O library never closes this file.
+     */
+    const stdout: LuaFile;
 
     /**
      * In case of success, returns a handle for a temporary file. This file is
@@ -125,6 +142,8 @@ declare namespace io {
      * Equivalent to io.output():write(···).
      */
     function write(...args: (string | number)[]): LuaMultiReturn<[LuaFile] | [undefined, string]>;
+
+    type FileReadFormatToType<T> = T extends FileReadNumberFormat ? number : string;
 }
 
 interface LuaFile {
@@ -157,12 +176,10 @@ interface LuaFile {
      * In case of errors this function raises the error, instead of returning an
      * error code.
      */
-    lines<T extends FileReadFormat[]>(
+    lines<T extends io.FileReadFormat[]>(
         ...formats: T
     ): LuaIterable<
-        LuaMultiReturn<
-            [] extends T ? [string] : { [P in keyof T]: T[P] extends 'n' ? number : string }
-        >
+        LuaMultiReturn<[] extends T ? [string] : { [P in keyof T]: io.FileReadFormatToType<T[P]> }>
     >;
 
     /**
@@ -193,9 +210,11 @@ interface LuaFile {
      *
      * The formats "l" and "L" should be used only for text files.
      */
-    read<T extends FileReadFormat[]>(
+    read(): io.FileReadFormatToType<io.FileReadLineFormat> | undefined;
+    read<T extends io.FileReadFormat>(format: T): io.FileReadFormatToType<T> | undefined;
+    read<T extends io.FileReadFormat[]>(
         ...formats: T
-    ): LuaMultiReturn<{ [P in keyof T]?: T[P] extends 'n' ? number : string }>;
+    ): LuaMultiReturn<{ [P in keyof T]?: io.FileReadFormatToType<T[P]> }>;
 
     /**
      * Sets and geionts the file position, measured from the beginning of the
diff --git a/core/metatable.d.ts b/core/metatable.d.ts
index fb411e5..7636dea 100644
--- a/core/metatable.d.ts
+++ b/core/metatable.d.ts
@@ -1,6 +1,6 @@
 // Based on https://www.lua.org/manual/5.3/manual.html#2.4
 
-interface LuaMetatable<T, TIndex = object> {
+interface LuaMetatable<T, TIndex extends object | ((this: T, key: any) => any) | undefined> {
     /**
      * the addition (+) operation. If any operand for an addition is not a number
      * (nor a string coercible to a number), Lua will try to call a metamethod.
@@ -102,7 +102,7 @@ interface LuaMetatable<T, TIndex = object> {
      * this table with key. (This indexing is regular, not raw, and therefore can
      * trigger another metamethod.)
      */
-    __index?: TIndex | ((this: T, key: any, value: any) => any);
+    __index?: TIndex;
 
     /**
      * The indexing assignment table[key] = value. Like the index event, this
diff --git a/core/string.d.ts b/core/string.d.ts
index 5310dad..0a10e5d 100644
--- a/core/string.d.ts
+++ b/core/string.d.ts
@@ -179,6 +179,11 @@ declare namespace string {
      */
     function match(s: string, pattern: string, init?: number): LuaMultiReturn<string[]>;
 
+    /**
+     * Returns a string that is the concatenation of `n` copies of the string `s`.
+     */
+    function rep(s: string, n: number): string;
+
     /**
      * Returns a string that is the string s reversed.
      */
diff --git a/special/5.1-only.d.ts b/special/5.1-only.d.ts
index ef13f0f..aeeadce 100644
--- a/special/5.1-only.d.ts
+++ b/special/5.1-only.d.ts
@@ -96,4 +96,8 @@ declare namespace debug {
     ): LuaMultiReturn<[string, any]>;
 }
 
-type FileReadFormat = '*n' | '*a' | '*l' | number;
+declare namespace io {
+    type FileReadNumberFormat = '*n';
+    type FileReadLineFormat = '*l';
+    type FileReadFormat = FileReadNumberFormat | FileReadLineFormat | '*a' | number;
+}
diff --git a/special/5.2-or-jit.d.ts b/special/5.2-or-jit.d.ts
index c2c8b88..5d3e3b8 100644
--- a/special/5.2-or-jit.d.ts
+++ b/special/5.2-or-jit.d.ts
@@ -1 +1,5 @@
-type FileReadFormat = '*n' | '*a' | '*l' | '*L' | number;
+declare namespace io {
+    type FileReadNumberFormat = '*n';
+    type FileReadLineFormat = '*l';
+    type FileReadFormat = FileReadNumberFormat | FileReadLineFormat | '*a' | '*L' | number;
+}
diff --git a/special/5.3-plus.d.ts b/special/5.3-plus.d.ts
index aec91af..802a43b 100644
--- a/special/5.3-plus.d.ts
+++ b/special/5.3-plus.d.ts
@@ -227,4 +227,8 @@ interface LuaMetatable<T> {
     __shr?(this: T, operand: any): any;
 }
 
-type FileReadFormat = 'n' | 'a' | 'l' | 'L' | number;
+declare namespace io {
+    type FileReadNumberFormat = 'n';
+    type FileReadLineFormat = 'l';
+    type FileReadFormat = FileReadNumberFormat | FileReadLineFormat | 'a' | 'L' | number;
+}
diff --git a/test/__snapshots__/global.spec.ts.snap b/test/__snapshots__/global.spec.ts.snap
index d84335f..ecc346b 100644
--- a/test/__snapshots__/global.spec.ts.snap
+++ b/test/__snapshots__/global.spec.ts.snap
@@ -4,11 +4,28 @@ exports[`Lua version 5.1 / global assert 1`] = `"assert({bla = \\"not false\\"})
 
 exports[`Lua version 5.1 / global assert 2`] = `"assert(false, \\"assert message\\")"`;
 
+exports[`Lua version 5.1 / global assert with multi-return 1`] = `
+"v, a, b = assert({bla = \\"not false\\"}, {foo = \\"FOO\\"}, {bar = \\"BAR\\"})
+bla = v.bla
+foo = a.foo
+bar = b.bar"
+`;
+
+exports[`Lua version 5.1 / global assert with return 1`] = `
+"v = assert({bla = \\"not false\\"})
+bla = v.bla"
+`;
+
 exports[`Lua version 5.1 / global getmetatable 1`] = `
 "metatable = getmetatable({})
 add = metatable.__add"
 `;
 
+exports[`Lua version 5.1 / global getmetatable on string 1`] = `
+"metatable = getmetatable(\\"foo\\")
+index = metatable.__index"
+`;
+
 exports[`Lua version 5.1 / global ipairs 1`] = `
 "for i, v in ipairs({1, 2, 3}) do
     print(i, v)
@@ -25,6 +42,18 @@ exports[`Lua version 5.1 / global pairs 1`] = `
 end"
 `;
 
+exports[`Lua version 5.1 / global pairs with LuaTable 1`] = `
+"tbl = {}
+tbl.foo = \\"bar\\"
+tbl.baz = \\"bur\\"
+takesStr = function(____, str)
+end
+for k, v in pairs(tbl) do
+    takesStr(_G, k)
+    takesStr(_G, v)
+end"
+`;
+
 exports[`Lua version 5.1 / global pcall 1`] = `
 "success, resultOrMessage = pcall(
     function(a) return true end,
@@ -52,6 +81,27 @@ exports[`Lua version 5.1 / global select destructured 1`] = `"b, c = select(2, \
 
 exports[`Lua version 5.1 / global select with # 1`] = `"count = select(\\"#\\", \\"a\\", \\"b\\", \\"c\\")"`;
 
+exports[`Lua version 5.1 / global setmetatable with function index 1`] = `
+"tbl = setmetatable(
+    {},
+    {
+        __index = function(____, key) return tostring(key) .. \\"bar\\" end
+    }
+)
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
+exports[`Lua version 5.1 / global setmetatable with no index 1`] = `"tbl = setmetatable({})"`;
+
+exports[`Lua version 5.1 / global setmetatable with table index 1`] = `
+"tbl = setmetatable({}, {__index = {foo = \\"bar\\"}})
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
 exports[`Lua version 5.1 / global tonumber 1`] = `"number = tonumber(\\"213.4\\")"`;
 
 exports[`Lua version 5.1 / global tonumber with base 1`] = `"number = tonumber(\\"213.4\\", 5)"`;
@@ -64,11 +114,28 @@ exports[`Lua version 5.2 / global assert 1`] = `"assert({bla = \\"not false\\"})
 
 exports[`Lua version 5.2 / global assert 2`] = `"assert(false, \\"assert message\\")"`;
 
+exports[`Lua version 5.2 / global assert with multi-return 1`] = `
+"v, a, b = assert({bla = \\"not false\\"}, {foo = \\"FOO\\"}, {bar = \\"BAR\\"})
+bla = v.bla
+foo = a.foo
+bar = b.bar"
+`;
+
+exports[`Lua version 5.2 / global assert with return 1`] = `
+"v = assert({bla = \\"not false\\"})
+bla = v.bla"
+`;
+
 exports[`Lua version 5.2 / global getmetatable 1`] = `
 "metatable = getmetatable({})
 add = metatable.__add"
 `;
 
+exports[`Lua version 5.2 / global getmetatable on string 1`] = `
+"metatable = getmetatable(\\"foo\\")
+index = metatable.__index"
+`;
+
 exports[`Lua version 5.2 / global ipairs 1`] = `
 "for i, v in ipairs({1, 2, 3}) do
     print(i, v)
@@ -85,6 +152,18 @@ exports[`Lua version 5.2 / global pairs 1`] = `
 end"
 `;
 
+exports[`Lua version 5.2 / global pairs with LuaTable 1`] = `
+"tbl = {}
+tbl.foo = \\"bar\\"
+tbl.baz = \\"bur\\"
+takesStr = function(____, str)
+end
+for k, v in pairs(tbl) do
+    takesStr(_G, k)
+    takesStr(_G, v)
+end"
+`;
+
 exports[`Lua version 5.2 / global pcall 1`] = `
 "success, resultOrMessage = pcall(
     function(a) return true end,
@@ -112,6 +191,27 @@ exports[`Lua version 5.2 / global select destructured 1`] = `"b, c = select(2, \
 
 exports[`Lua version 5.2 / global select with # 1`] = `"count = select(\\"#\\", \\"a\\", \\"b\\", \\"c\\")"`;
 
+exports[`Lua version 5.2 / global setmetatable with function index 1`] = `
+"tbl = setmetatable(
+    {},
+    {
+        __index = function(____, key) return tostring(key) .. \\"bar\\" end
+    }
+)
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
+exports[`Lua version 5.2 / global setmetatable with no index 1`] = `"tbl = setmetatable({})"`;
+
+exports[`Lua version 5.2 / global setmetatable with table index 1`] = `
+"tbl = setmetatable({}, {__index = {foo = \\"bar\\"}})
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
 exports[`Lua version 5.2 / global tonumber 1`] = `"number = tonumber(\\"213.4\\")"`;
 
 exports[`Lua version 5.2 / global tonumber with base 1`] = `"number = tonumber(\\"213.4\\", 5)"`;
@@ -124,11 +224,28 @@ exports[`Lua version 5.3 / global assert 1`] = `"assert({bla = \\"not false\\"})
 
 exports[`Lua version 5.3 / global assert 2`] = `"assert(false, \\"assert message\\")"`;
 
+exports[`Lua version 5.3 / global assert with multi-return 1`] = `
+"v, a, b = assert({bla = \\"not false\\"}, {foo = \\"FOO\\"}, {bar = \\"BAR\\"})
+bla = v.bla
+foo = a.foo
+bar = b.bar"
+`;
+
+exports[`Lua version 5.3 / global assert with return 1`] = `
+"v = assert({bla = \\"not false\\"})
+bla = v.bla"
+`;
+
 exports[`Lua version 5.3 / global getmetatable 1`] = `
 "metatable = getmetatable({})
 add = metatable.__add"
 `;
 
+exports[`Lua version 5.3 / global getmetatable on string 1`] = `
+"metatable = getmetatable(\\"foo\\")
+index = metatable.__index"
+`;
+
 exports[`Lua version 5.3 / global ipairs 1`] = `
 "for i, v in ipairs({1, 2, 3}) do
     print(i, v)
@@ -145,6 +262,18 @@ exports[`Lua version 5.3 / global pairs 1`] = `
 end"
 `;
 
+exports[`Lua version 5.3 / global pairs with LuaTable 1`] = `
+"tbl = {}
+tbl.foo = \\"bar\\"
+tbl.baz = \\"bur\\"
+takesStr = function(____, str)
+end
+for k, v in pairs(tbl) do
+    takesStr(_G, k)
+    takesStr(_G, v)
+end"
+`;
+
 exports[`Lua version 5.3 / global pcall 1`] = `
 "success, resultOrMessage = pcall(
     function(a) return true end,
@@ -172,6 +301,27 @@ exports[`Lua version 5.3 / global select destructured 1`] = `"b, c = select(2, \
 
 exports[`Lua version 5.3 / global select with # 1`] = `"count = select(\\"#\\", \\"a\\", \\"b\\", \\"c\\")"`;
 
+exports[`Lua version 5.3 / global setmetatable with function index 1`] = `
+"tbl = setmetatable(
+    {},
+    {
+        __index = function(____, key) return tostring(key) .. \\"bar\\" end
+    }
+)
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
+exports[`Lua version 5.3 / global setmetatable with no index 1`] = `"tbl = setmetatable({})"`;
+
+exports[`Lua version 5.3 / global setmetatable with table index 1`] = `
+"tbl = setmetatable({}, {__index = {foo = \\"bar\\"}})
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
 exports[`Lua version 5.3 / global tonumber 1`] = `"number = tonumber(\\"213.4\\")"`;
 
 exports[`Lua version 5.3 / global tonumber with base 1`] = `"number = tonumber(\\"213.4\\", 5)"`;
@@ -184,11 +334,28 @@ exports[`Lua version 5.4 / global assert 1`] = `"assert({bla = \\"not false\\"})
 
 exports[`Lua version 5.4 / global assert 2`] = `"assert(false, \\"assert message\\")"`;
 
+exports[`Lua version 5.4 / global assert with multi-return 1`] = `
+"v, a, b = assert({bla = \\"not false\\"}, {foo = \\"FOO\\"}, {bar = \\"BAR\\"})
+bla = v.bla
+foo = a.foo
+bar = b.bar"
+`;
+
+exports[`Lua version 5.4 / global assert with return 1`] = `
+"v = assert({bla = \\"not false\\"})
+bla = v.bla"
+`;
+
 exports[`Lua version 5.4 / global getmetatable 1`] = `
 "metatable = getmetatable({})
 add = metatable.__add"
 `;
 
+exports[`Lua version 5.4 / global getmetatable on string 1`] = `
+"metatable = getmetatable(\\"foo\\")
+index = metatable.__index"
+`;
+
 exports[`Lua version 5.4 / global ipairs 1`] = `
 "for i, v in ipairs({1, 2, 3}) do
     print(i, v)
@@ -205,6 +372,18 @@ exports[`Lua version 5.4 / global pairs 1`] = `
 end"
 `;
 
+exports[`Lua version 5.4 / global pairs with LuaTable 1`] = `
+"tbl = {}
+tbl.foo = \\"bar\\"
+tbl.baz = \\"bur\\"
+takesStr = function(____, str)
+end
+for k, v in pairs(tbl) do
+    takesStr(_G, k)
+    takesStr(_G, v)
+end"
+`;
+
 exports[`Lua version 5.4 / global pcall 1`] = `
 "success, resultOrMessage = pcall(
     function(a) return true end,
@@ -232,6 +411,27 @@ exports[`Lua version 5.4 / global select destructured 1`] = `"b, c = select(2, \
 
 exports[`Lua version 5.4 / global select with # 1`] = `"count = select(\\"#\\", \\"a\\", \\"b\\", \\"c\\")"`;
 
+exports[`Lua version 5.4 / global setmetatable with function index 1`] = `
+"tbl = setmetatable(
+    {},
+    {
+        __index = function(____, key) return tostring(key) .. \\"bar\\" end
+    }
+)
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
+exports[`Lua version 5.4 / global setmetatable with no index 1`] = `"tbl = setmetatable({})"`;
+
+exports[`Lua version 5.4 / global setmetatable with table index 1`] = `
+"tbl = setmetatable({}, {__index = {foo = \\"bar\\"}})
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
 exports[`Lua version 5.4 / global tonumber 1`] = `"number = tonumber(\\"213.4\\")"`;
 
 exports[`Lua version 5.4 / global tonumber with base 1`] = `"number = tonumber(\\"213.4\\", 5)"`;
@@ -244,11 +444,28 @@ exports[`Lua version JIT / global assert 1`] = `"assert({bla = \\"not false\\"})
 
 exports[`Lua version JIT / global assert 2`] = `"assert(false, \\"assert message\\")"`;
 
+exports[`Lua version JIT / global assert with multi-return 1`] = `
+"v, a, b = assert({bla = \\"not false\\"}, {foo = \\"FOO\\"}, {bar = \\"BAR\\"})
+bla = v.bla
+foo = a.foo
+bar = b.bar"
+`;
+
+exports[`Lua version JIT / global assert with return 1`] = `
+"v = assert({bla = \\"not false\\"})
+bla = v.bla"
+`;
+
 exports[`Lua version JIT / global getmetatable 1`] = `
 "metatable = getmetatable({})
 add = metatable.__add"
 `;
 
+exports[`Lua version JIT / global getmetatable on string 1`] = `
+"metatable = getmetatable(\\"foo\\")
+index = metatable.__index"
+`;
+
 exports[`Lua version JIT / global ipairs 1`] = `
 "for i, v in ipairs({1, 2, 3}) do
     print(i, v)
@@ -265,6 +482,18 @@ exports[`Lua version JIT / global pairs 1`] = `
 end"
 `;
 
+exports[`Lua version JIT / global pairs with LuaTable 1`] = `
+"tbl = {}
+tbl.foo = \\"bar\\"
+tbl.baz = \\"bur\\"
+takesStr = function(____, str)
+end
+for k, v in pairs(tbl) do
+    takesStr(_G, k)
+    takesStr(_G, v)
+end"
+`;
+
 exports[`Lua version JIT / global pcall 1`] = `
 "success, resultOrMessage = pcall(
     function(a) return true end,
@@ -292,6 +521,27 @@ exports[`Lua version JIT / global select destructured 1`] = `"b, c = select(2, \
 
 exports[`Lua version JIT / global select with # 1`] = `"count = select(\\"#\\", \\"a\\", \\"b\\", \\"c\\")"`;
 
+exports[`Lua version JIT / global setmetatable with function index 1`] = `
+"tbl = setmetatable(
+    {},
+    {
+        __index = function(____, key) return tostring(key) .. \\"bar\\" end
+    }
+)
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
+exports[`Lua version JIT / global setmetatable with no index 1`] = `"tbl = setmetatable({})"`;
+
+exports[`Lua version JIT / global setmetatable with table index 1`] = `
+"tbl = setmetatable({}, {__index = {foo = \\"bar\\"}})
+takesStr = function(____, s)
+end
+takesStr(_G, tbl.foo)"
+`;
+
 exports[`Lua version JIT / global tonumber 1`] = `"number = tonumber(\\"213.4\\")"`;
 
 exports[`Lua version JIT / global tonumber with base 1`] = `"number = tonumber(\\"213.4\\", 5)"`;
diff --git a/test/__snapshots__/io.spec.ts.snap b/test/__snapshots__/io.spec.ts.snap
new file mode 100644
index 0000000..e44aaf4
--- /dev/null
+++ b/test/__snapshots__/io.spec.ts.snap
@@ -0,0 +1,531 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Lua version 5.1 / file close 1`] = `"file:close()"`;
+
+exports[`Lua version 5.1 / file flush 1`] = `"file:flush()"`;
+
+exports[`Lua version 5.1 / file lines 1`] = `
+"for line in file:lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.1 / file read multi 1`] = `
+"foo, bar = file:read(\\"*l\\", \\"*n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version 5.1 / file read one 1`] = `
+"foo = file:read(\\"*l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.1 / file read zero 1`] = `
+"foo = file:read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.1 / file seek 1`] = `"pos, err = file:seek()"`;
+
+exports[`Lua version 5.1 / file seek offset 1`] = `"pos, err = file:seek(\\"cur\\", 1)"`;
+
+exports[`Lua version 5.1 / file seek whence 1`] = `"pos, err = file:seek(\\"cur\\")"`;
+
+exports[`Lua version 5.1 / file setvbuf 1`] = `"file:setvbuf(\\"no\\")"`;
+
+exports[`Lua version 5.1 / file setvbuf with size 1`] = `"file:setvbuf(\\"line\\", 10)"`;
+
+exports[`Lua version 5.1 / file write 1`] = `"f, err = file:write(\\"foo\\", \\"bar\\")"`;
+
+exports[`Lua version 5.1 / io close 1`] = `"io.close()"`;
+
+exports[`Lua version 5.1 / io close file 1`] = `"io.close(file)"`;
+
+exports[`Lua version 5.1 / io flush 1`] = `"io.flush()"`;
+
+exports[`Lua version 5.1 / io input 1`] = `"inp = io.input()"`;
+
+exports[`Lua version 5.1 / io input with file handle 1`] = `"inp = io.input(file)"`;
+
+exports[`Lua version 5.1 / io input with filename 1`] = `"inp = io.input(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.1 / io lines 1`] = `
+"for line in io.lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.1 / io lines with filename 1`] = `
+"for line in io.lines(\\"foo.bar\\") do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.1 / io open 1`] = `"f, err = io.open(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.1 / io open with mode flag 1`] = `"f, err = io.open(\\"foo.bar\\", \\"r\\")"`;
+
+exports[`Lua version 5.1 / io output 1`] = `"inp = io.output()"`;
+
+exports[`Lua version 5.1 / io output with file handle 1`] = `"inp = io.output(file)"`;
+
+exports[`Lua version 5.1 / io output with filename 1`] = `"inp = io.output(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.1 / io popen 1`] = `"proc, err = io.popen(\\"echo foobar\\")"`;
+
+exports[`Lua version 5.1 / io read multi 1`] = `
+"foo, bar = io.read(\\"*l\\", \\"*n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version 5.1 / io read one 1`] = `
+"foo = io.read(\\"*l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.1 / io read zero 1`] = `
+"foo = io.read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.1 / io stderr 1`] = `"io.stderr:write(\\"foobar\\")"`;
+
+exports[`Lua version 5.1 / io stdin 1`] = `"input = io.stdin:read()"`;
+
+exports[`Lua version 5.1 / io stdout 1`] = `"io.stdout:write(\\"foobar\\")"`;
+
+exports[`Lua version 5.1 / io tmpfile 1`] = `"file = io.tmpfile()"`;
+
+exports[`Lua version 5.1 / io type 1`] = `
+"print(
+    io.type(file)
+)"
+`;
+
+exports[`Lua version 5.1 / io write 1`] = `"f, err = io.write(\\"foobar\\")"`;
+
+exports[`Lua version 5.2 / file close 1`] = `"file:close()"`;
+
+exports[`Lua version 5.2 / file flush 1`] = `"file:flush()"`;
+
+exports[`Lua version 5.2 / file lines 1`] = `
+"for line in file:lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.2 / file read multi 1`] = `
+"foo, bar = file:read(\\"*l\\", \\"*n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version 5.2 / file read one 1`] = `
+"foo = file:read(\\"*l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.2 / file read zero 1`] = `
+"foo = file:read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.2 / file seek 1`] = `"pos, err = file:seek()"`;
+
+exports[`Lua version 5.2 / file seek offset 1`] = `"pos, err = file:seek(\\"cur\\", 1)"`;
+
+exports[`Lua version 5.2 / file seek whence 1`] = `"pos, err = file:seek(\\"cur\\")"`;
+
+exports[`Lua version 5.2 / file setvbuf 1`] = `"file:setvbuf(\\"no\\")"`;
+
+exports[`Lua version 5.2 / file setvbuf with size 1`] = `"file:setvbuf(\\"line\\", 10)"`;
+
+exports[`Lua version 5.2 / file write 1`] = `"f, err = file:write(\\"foo\\", \\"bar\\")"`;
+
+exports[`Lua version 5.2 / io close 1`] = `"io.close()"`;
+
+exports[`Lua version 5.2 / io close file 1`] = `"io.close(file)"`;
+
+exports[`Lua version 5.2 / io flush 1`] = `"io.flush()"`;
+
+exports[`Lua version 5.2 / io input 1`] = `"inp = io.input()"`;
+
+exports[`Lua version 5.2 / io input with file handle 1`] = `"inp = io.input(file)"`;
+
+exports[`Lua version 5.2 / io input with filename 1`] = `"inp = io.input(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.2 / io lines 1`] = `
+"for line in io.lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.2 / io lines with filename 1`] = `
+"for line in io.lines(\\"foo.bar\\") do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.2 / io open 1`] = `"f, err = io.open(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.2 / io open with mode flag 1`] = `"f, err = io.open(\\"foo.bar\\", \\"r\\")"`;
+
+exports[`Lua version 5.2 / io output 1`] = `"inp = io.output()"`;
+
+exports[`Lua version 5.2 / io output with file handle 1`] = `"inp = io.output(file)"`;
+
+exports[`Lua version 5.2 / io output with filename 1`] = `"inp = io.output(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.2 / io popen 1`] = `"proc, err = io.popen(\\"echo foobar\\")"`;
+
+exports[`Lua version 5.2 / io read multi 1`] = `
+"foo, bar = io.read(\\"*l\\", \\"*n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version 5.2 / io read one 1`] = `
+"foo = io.read(\\"*l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.2 / io read zero 1`] = `
+"foo = io.read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.2 / io stderr 1`] = `"io.stderr:write(\\"foobar\\")"`;
+
+exports[`Lua version 5.2 / io stdin 1`] = `"input = io.stdin:read()"`;
+
+exports[`Lua version 5.2 / io stdout 1`] = `"io.stdout:write(\\"foobar\\")"`;
+
+exports[`Lua version 5.2 / io tmpfile 1`] = `"file = io.tmpfile()"`;
+
+exports[`Lua version 5.2 / io type 1`] = `
+"print(
+    io.type(file)
+)"
+`;
+
+exports[`Lua version 5.2 / io write 1`] = `"f, err = io.write(\\"foobar\\")"`;
+
+exports[`Lua version 5.3 / file close 1`] = `"file:close()"`;
+
+exports[`Lua version 5.3 / file flush 1`] = `"file:flush()"`;
+
+exports[`Lua version 5.3 / file lines 1`] = `
+"for line in file:lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.3 / file read multi 1`] = `
+"foo, bar = file:read(\\"l\\", \\"n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version 5.3 / file read one 1`] = `
+"foo = file:read(\\"l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.3 / file read zero 1`] = `
+"foo = file:read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.3 / file seek 1`] = `"pos, err = file:seek()"`;
+
+exports[`Lua version 5.3 / file seek offset 1`] = `"pos, err = file:seek(\\"cur\\", 1)"`;
+
+exports[`Lua version 5.3 / file seek whence 1`] = `"pos, err = file:seek(\\"cur\\")"`;
+
+exports[`Lua version 5.3 / file setvbuf 1`] = `"file:setvbuf(\\"no\\")"`;
+
+exports[`Lua version 5.3 / file setvbuf with size 1`] = `"file:setvbuf(\\"line\\", 10)"`;
+
+exports[`Lua version 5.3 / file write 1`] = `"f, err = file:write(\\"foo\\", \\"bar\\")"`;
+
+exports[`Lua version 5.3 / io close 1`] = `"io.close()"`;
+
+exports[`Lua version 5.3 / io close file 1`] = `"io.close(file)"`;
+
+exports[`Lua version 5.3 / io flush 1`] = `"io.flush()"`;
+
+exports[`Lua version 5.3 / io input 1`] = `"inp = io.input()"`;
+
+exports[`Lua version 5.3 / io input with file handle 1`] = `"inp = io.input(file)"`;
+
+exports[`Lua version 5.3 / io input with filename 1`] = `"inp = io.input(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.3 / io lines 1`] = `
+"for line in io.lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.3 / io lines with filename 1`] = `
+"for line in io.lines(\\"foo.bar\\") do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.3 / io open 1`] = `"f, err = io.open(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.3 / io open with mode flag 1`] = `"f, err = io.open(\\"foo.bar\\", \\"r\\")"`;
+
+exports[`Lua version 5.3 / io output 1`] = `"inp = io.output()"`;
+
+exports[`Lua version 5.3 / io output with file handle 1`] = `"inp = io.output(file)"`;
+
+exports[`Lua version 5.3 / io output with filename 1`] = `"inp = io.output(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.3 / io popen 1`] = `"proc, err = io.popen(\\"echo foobar\\")"`;
+
+exports[`Lua version 5.3 / io read multi 1`] = `
+"foo, bar = io.read(\\"l\\", \\"n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version 5.3 / io read one 1`] = `
+"foo = io.read(\\"l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.3 / io read zero 1`] = `
+"foo = io.read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.3 / io stderr 1`] = `"io.stderr:write(\\"foobar\\")"`;
+
+exports[`Lua version 5.3 / io stdin 1`] = `"input = io.stdin:read()"`;
+
+exports[`Lua version 5.3 / io stdout 1`] = `"io.stdout:write(\\"foobar\\")"`;
+
+exports[`Lua version 5.3 / io tmpfile 1`] = `"file = io.tmpfile()"`;
+
+exports[`Lua version 5.3 / io type 1`] = `
+"print(
+    io.type(file)
+)"
+`;
+
+exports[`Lua version 5.3 / io write 1`] = `"f, err = io.write(\\"foobar\\")"`;
+
+exports[`Lua version 5.4 / file close 1`] = `"file:close()"`;
+
+exports[`Lua version 5.4 / file flush 1`] = `"file:flush()"`;
+
+exports[`Lua version 5.4 / file lines 1`] = `
+"for line in file:lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.4 / file read multi 1`] = `
+"foo, bar = file:read(\\"l\\", \\"n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version 5.4 / file read one 1`] = `
+"foo = file:read(\\"l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.4 / file read zero 1`] = `
+"foo = file:read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.4 / file seek 1`] = `"pos, err = file:seek()"`;
+
+exports[`Lua version 5.4 / file seek offset 1`] = `"pos, err = file:seek(\\"cur\\", 1)"`;
+
+exports[`Lua version 5.4 / file seek whence 1`] = `"pos, err = file:seek(\\"cur\\")"`;
+
+exports[`Lua version 5.4 / file setvbuf 1`] = `"file:setvbuf(\\"no\\")"`;
+
+exports[`Lua version 5.4 / file setvbuf with size 1`] = `"file:setvbuf(\\"line\\", 10)"`;
+
+exports[`Lua version 5.4 / file write 1`] = `"f, err = file:write(\\"foo\\", \\"bar\\")"`;
+
+exports[`Lua version 5.4 / io close 1`] = `"io.close()"`;
+
+exports[`Lua version 5.4 / io close file 1`] = `"io.close(file)"`;
+
+exports[`Lua version 5.4 / io flush 1`] = `"io.flush()"`;
+
+exports[`Lua version 5.4 / io input 1`] = `"inp = io.input()"`;
+
+exports[`Lua version 5.4 / io input with file handle 1`] = `"inp = io.input(file)"`;
+
+exports[`Lua version 5.4 / io input with filename 1`] = `"inp = io.input(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.4 / io lines 1`] = `
+"for line in io.lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.4 / io lines with filename 1`] = `
+"for line in io.lines(\\"foo.bar\\") do
+    print(line)
+end"
+`;
+
+exports[`Lua version 5.4 / io open 1`] = `"f, err = io.open(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.4 / io open with mode flag 1`] = `"f, err = io.open(\\"foo.bar\\", \\"r\\")"`;
+
+exports[`Lua version 5.4 / io output 1`] = `"inp = io.output()"`;
+
+exports[`Lua version 5.4 / io output with file handle 1`] = `"inp = io.output(file)"`;
+
+exports[`Lua version 5.4 / io output with filename 1`] = `"inp = io.output(\\"foo.bar\\")"`;
+
+exports[`Lua version 5.4 / io popen 1`] = `"proc, err = io.popen(\\"echo foobar\\")"`;
+
+exports[`Lua version 5.4 / io read multi 1`] = `
+"foo, bar = io.read(\\"l\\", \\"n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version 5.4 / io read one 1`] = `
+"foo = io.read(\\"l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.4 / io read zero 1`] = `
+"foo = io.read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version 5.4 / io stderr 1`] = `"io.stderr:write(\\"foobar\\")"`;
+
+exports[`Lua version 5.4 / io stdin 1`] = `"input = io.stdin:read()"`;
+
+exports[`Lua version 5.4 / io stdout 1`] = `"io.stdout:write(\\"foobar\\")"`;
+
+exports[`Lua version 5.4 / io tmpfile 1`] = `"file = io.tmpfile()"`;
+
+exports[`Lua version 5.4 / io type 1`] = `
+"print(
+    io.type(file)
+)"
+`;
+
+exports[`Lua version 5.4 / io write 1`] = `"f, err = io.write(\\"foobar\\")"`;
+
+exports[`Lua version JIT / file close 1`] = `"file:close()"`;
+
+exports[`Lua version JIT / file flush 1`] = `"file:flush()"`;
+
+exports[`Lua version JIT / file lines 1`] = `
+"for line in file:lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version JIT / file read multi 1`] = `
+"foo, bar = file:read(\\"*l\\", \\"*n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version JIT / file read one 1`] = `
+"foo = file:read(\\"*l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version JIT / file read zero 1`] = `
+"foo = file:read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version JIT / file seek 1`] = `"pos, err = file:seek()"`;
+
+exports[`Lua version JIT / file seek offset 1`] = `"pos, err = file:seek(\\"cur\\", 1)"`;
+
+exports[`Lua version JIT / file seek whence 1`] = `"pos, err = file:seek(\\"cur\\")"`;
+
+exports[`Lua version JIT / file setvbuf 1`] = `"file:setvbuf(\\"no\\")"`;
+
+exports[`Lua version JIT / file setvbuf with size 1`] = `"file:setvbuf(\\"line\\", 10)"`;
+
+exports[`Lua version JIT / file write 1`] = `"f, err = file:write(\\"foo\\", \\"bar\\")"`;
+
+exports[`Lua version JIT / io close 1`] = `"io.close()"`;
+
+exports[`Lua version JIT / io close file 1`] = `"io.close(file)"`;
+
+exports[`Lua version JIT / io flush 1`] = `"io.flush()"`;
+
+exports[`Lua version JIT / io input 1`] = `"inp = io.input()"`;
+
+exports[`Lua version JIT / io input with file handle 1`] = `"inp = io.input(file)"`;
+
+exports[`Lua version JIT / io input with filename 1`] = `"inp = io.input(\\"foo.bar\\")"`;
+
+exports[`Lua version JIT / io lines 1`] = `
+"for line in io.lines() do
+    print(line)
+end"
+`;
+
+exports[`Lua version JIT / io lines with filename 1`] = `
+"for line in io.lines(\\"foo.bar\\") do
+    print(line)
+end"
+`;
+
+exports[`Lua version JIT / io open 1`] = `"f, err = io.open(\\"foo.bar\\")"`;
+
+exports[`Lua version JIT / io open with mode flag 1`] = `"f, err = io.open(\\"foo.bar\\", \\"r\\")"`;
+
+exports[`Lua version JIT / io output 1`] = `"inp = io.output()"`;
+
+exports[`Lua version JIT / io output with file handle 1`] = `"inp = io.output(file)"`;
+
+exports[`Lua version JIT / io output with filename 1`] = `"inp = io.output(\\"foo.bar\\")"`;
+
+exports[`Lua version JIT / io popen 1`] = `"proc, err = io.popen(\\"echo foobar\\")"`;
+
+exports[`Lua version JIT / io read multi 1`] = `
+"foo, bar = io.read(\\"*l\\", \\"*n\\")
+takesString(_G, foo)
+takesNumber(_G, bar)"
+`;
+
+exports[`Lua version JIT / io read one 1`] = `
+"foo = io.read(\\"*l\\")
+takesString(_G, foo)"
+`;
+
+exports[`Lua version JIT / io read zero 1`] = `
+"foo = io.read()
+takesString(_G, foo)"
+`;
+
+exports[`Lua version JIT / io stderr 1`] = `"io.stderr:write(\\"foobar\\")"`;
+
+exports[`Lua version JIT / io stdin 1`] = `"input = io.stdin:read()"`;
+
+exports[`Lua version JIT / io stdout 1`] = `"io.stdout:write(\\"foobar\\")"`;
+
+exports[`Lua version JIT / io tmpfile 1`] = `"file = io.tmpfile()"`;
+
+exports[`Lua version JIT / io type 1`] = `
+"print(
+    io.type(file)
+)"
+`;
+
+exports[`Lua version JIT / io write 1`] = `"f, err = io.write(\\"foobar\\")"`;
diff --git a/test/__snapshots__/string.spec.ts.snap b/test/__snapshots__/string.spec.ts.snap
index 8b0631e..38517fc 100644
--- a/test/__snapshots__/string.spec.ts.snap
+++ b/test/__snapshots__/string.spec.ts.snap
@@ -70,6 +70,8 @@ exports[`Lua version 5.1 / string string.match 1`] = `
 
 exports[`Lua version 5.1 / string string.match destructured 1`] = `"match1, match2 = string.match(\\"hello world\\", \\"l\\")"`;
 
+exports[`Lua version 5.1 / string string.rep 1`] = `"str = string.rep(\\"foo\\", 3)"`;
+
 exports[`Lua version 5.2 / string string.byte 1`] = `"b = string.byte(\\"d\\")"`;
 
 exports[`Lua version 5.2 / string string.byte multiple 1`] = `"a, b, c, d = string.byte(\\"abcd\\", 1, 4)"`;
@@ -140,6 +142,8 @@ exports[`Lua version 5.2 / string string.match 1`] = `
 
 exports[`Lua version 5.2 / string string.match destructured 1`] = `"match1, match2 = string.match(\\"hello world\\", \\"l\\")"`;
 
+exports[`Lua version 5.2 / string string.rep 1`] = `"str = string.rep(\\"foo\\", 3)"`;
+
 exports[`Lua version 5.3 / string string.byte 1`] = `"b = string.byte(\\"d\\")"`;
 
 exports[`Lua version 5.3 / string string.byte multiple 1`] = `"a, b, c, d = string.byte(\\"abcd\\", 1, 4)"`;
@@ -210,6 +214,8 @@ exports[`Lua version 5.3 / string string.match 1`] = `
 
 exports[`Lua version 5.3 / string string.match destructured 1`] = `"match1, match2 = string.match(\\"hello world\\", \\"l\\")"`;
 
+exports[`Lua version 5.3 / string string.rep 1`] = `"str = string.rep(\\"foo\\", 3)"`;
+
 exports[`Lua version 5.4 / string string.byte 1`] = `"b = string.byte(\\"d\\")"`;
 
 exports[`Lua version 5.4 / string string.byte multiple 1`] = `"a, b, c, d = string.byte(\\"abcd\\", 1, 4)"`;
@@ -280,6 +286,8 @@ exports[`Lua version 5.4 / string string.match 1`] = `
 
 exports[`Lua version 5.4 / string string.match destructured 1`] = `"match1, match2 = string.match(\\"hello world\\", \\"l\\")"`;
 
+exports[`Lua version 5.4 / string string.rep 1`] = `"str = string.rep(\\"foo\\", 3)"`;
+
 exports[`Lua version JIT / string string.byte 1`] = `"b = string.byte(\\"d\\")"`;
 
 exports[`Lua version JIT / string string.byte multiple 1`] = `"a, b, c, d = string.byte(\\"abcd\\", 1, 4)"`;
@@ -349,3 +357,5 @@ exports[`Lua version JIT / string string.match 1`] = `
 `;
 
 exports[`Lua version JIT / string string.match destructured 1`] = `"match1, match2 = string.match(\\"hello world\\", \\"l\\")"`;
+
+exports[`Lua version JIT / string string.rep 1`] = `"str = string.rep(\\"foo\\", 3)"`;
diff --git a/test/global.spec.ts b/test/global.spec.ts
index f74e8a2..7b55c96 100644
--- a/test/global.spec.ts
+++ b/test/global.spec.ts
@@ -12,6 +12,32 @@ describeForEachLuaTarget('global', (target) => {
         expect(lua).toMatchSnapshot();
     });
 
+    test('assert with return', () => {
+        const lua = tstl(
+            target,
+            `
+            const v = assert({ bla: "not false"});
+            const bla = v.bla;
+        `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('assert with multi-return', () => {
+        const lua = tstl(
+            target,
+            `
+            const [v, a, b] = assert({ bla: "not false"}, { foo: "FOO" }, { bar: "BAR" });
+            const bla = v.bla;
+            const foo = a.foo;
+            const bar = b.bar;
+        `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
     test('assert', () => {
         const lua = tstl(
             target,
@@ -35,6 +61,18 @@ describeForEachLuaTarget('global', (target) => {
         expect(lua).toMatchSnapshot();
     });
 
+    test('getmetatable on string', () => {
+        const lua = tstl(
+            target,
+            `
+            const metatable = getmetatable("foo");
+            const index = metatable!.__index;
+        `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
     test('ipairs', () => {
         const lua = tstl(
             target,
@@ -83,6 +121,24 @@ describeForEachLuaTarget('global', (target) => {
         expect(lua).toMatchSnapshot();
     });
 
+    test('pairs with LuaTable', () => {
+        const lua = tstl(
+            target,
+            `
+            const tbl = new LuaTable<string, string>();
+            tbl.set("foo", "bar");
+            tbl.set("baz", "bur");
+            const takesStr = (str: string) => {};
+            for (const [k, v] of pairs(tbl)) {
+                takesStr(k);
+                takesStr(v);
+            }
+        `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
     test('pcall', () => {
         const lua = tstl(
             target,
@@ -149,6 +205,43 @@ describeForEachLuaTarget('global', (target) => {
         expect(lua).toMatchSnapshot();
     });
 
+    test('setmetatable with table index', () => {
+        const lua = tstl(
+            target,
+            `
+            const tbl = setmetatable({}, {__index: {foo: "bar"}});
+            const takesStr = (s: string) => {};
+            takesStr(tbl.foo);
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('setmetatable with function index', () => {
+        const lua = tstl(
+            target,
+            `
+            const tbl = setmetatable({}, {__index: (key: string) => key + "bar"});
+            const takesStr = (s: string) => {};
+            takesStr(tbl.foo);
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('setmetatable with no index', () => {
+        const lua = tstl(
+            target,
+            `
+            const tbl = setmetatable({});
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
     test('tonumber', () => {
         const lua = tstl(
             target,
diff --git a/test/io.spec.ts b/test/io.spec.ts
new file mode 100644
index 0000000..be52338
--- /dev/null
+++ b/test/io.spec.ts
@@ -0,0 +1,451 @@
+import { LuaTarget } from 'typescript-to-lua';
+import { describeForEachLuaTarget, tstl } from './test-utils';
+
+describeForEachLuaTarget('io', (target) => {
+    test('close', () => {
+        const lua = tstl(
+            target,
+            `
+            io.close();
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('close file', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            io.close(file);
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('flush', () => {
+        const lua = tstl(
+            target,
+            `
+            io.flush();
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('input', () => {
+        const lua = tstl(
+            target,
+            `
+            const inp = io.input();
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('input with filename', () => {
+        const lua = tstl(
+            target,
+            `
+            const inp = io.input("foo.bar");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('input with file handle', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            const inp = io.input(file);
+        `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('lines', () => {
+        const lua = tstl(
+            target,
+            `
+            for (const [line] of io.lines()) {
+                print(line);
+            }
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('lines with filename', () => {
+        const lua = tstl(
+            target,
+            `
+            for (const [line] of io.lines("foo.bar")) {
+                print(line);
+            }
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('open', () => {
+        const lua = tstl(
+            target,
+            `
+            const [f, err] = io.open("foo.bar");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('open with mode flag', () => {
+        const lua = tstl(
+            target,
+            `
+            const [f, err] = io.open("foo.bar", "r");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('output', () => {
+        const lua = tstl(
+            target,
+            `
+            const inp = io.output();
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('output with filename', () => {
+        const lua = tstl(
+            target,
+            `
+            const inp = io.output("foo.bar");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('output with file handle', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            const inp = io.output(file);
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('popen', () => {
+        const lua = tstl(
+            target,
+            `
+            const [proc, err] = io.popen("echo foobar");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('read zero', () => {
+        const lua = tstl(
+            target,
+            `
+            const foo = io.read();
+            declare function takesString(str: string): void;
+            takesString(foo);
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('read one', () => {
+        const useOldFormat =
+            [LuaTarget.Lua51, LuaTarget.Lua52, LuaTarget.LuaJIT, LuaTarget.Universal].indexOf(
+                target
+            ) >= 0;
+        const lineFormat = useOldFormat ? '*l' : 'l';
+        const lua = tstl(
+            target,
+            `
+            const foo = io.read("${lineFormat}");
+            declare function takesString(str: string): void;
+            takesString(foo);
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('read multi', () => {
+        const useOldFormat =
+            [LuaTarget.Lua51, LuaTarget.Lua52, LuaTarget.LuaJIT, LuaTarget.Universal].indexOf(
+                target
+            ) >= 0;
+        const numberFormat = useOldFormat ? '*n' : 'n';
+        const lineFormat = useOldFormat ? '*l' : 'l';
+        const lua = tstl(
+            target,
+            `
+            const [foo, bar] = io.read("${lineFormat}", "${numberFormat}");
+            declare function takesString(str: string): void;
+            declare function takesNumber(num: number): void;
+            takesString(foo);
+            takesNumber(bar);
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('stderr', () => {
+        const lua = tstl(
+            target,
+            `
+            io.stderr.write("foobar");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('stdin', () => {
+        const lua = tstl(
+            target,
+            `
+            const input = io.stdin.read();
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('stdout', () => {
+        const lua = tstl(
+            target,
+            `
+            io.stdout.write("foobar");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('tmpfile', () => {
+        const lua = tstl(
+            target,
+            `
+            const file = io.tmpfile();
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('type', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            print(io.type(file));
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('write', () => {
+        const lua = tstl(
+            target,
+            `
+            const [f, err] = io.write("foobar");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+});
+
+describeForEachLuaTarget('file', (target) => {
+    test('close', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            file.close();
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('flush', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            file.flush();
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('lines', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            for (const [line] of file.lines()) {
+                print(line);
+            }
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('read zero', () => {
+        const lua = tstl(
+            target,
+            `
+          declare const file: LuaFile;
+          const foo = file.read();
+          declare function takesString(str: string): void;
+          takesString(foo);
+          `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('read one', () => {
+        const useOldFormat =
+            [LuaTarget.Lua51, LuaTarget.Lua52, LuaTarget.LuaJIT, LuaTarget.Universal].indexOf(
+                target
+            ) >= 0;
+        const lineFormat = useOldFormat ? '*l' : 'l';
+        const lua = tstl(
+            target,
+            `
+          declare const file: LuaFile;
+          const foo = file.read("${lineFormat}");
+          declare function takesString(str: string): void;
+          takesString(foo);
+          `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('read multi', () => {
+        const useOldFormat =
+            [LuaTarget.Lua51, LuaTarget.Lua52, LuaTarget.LuaJIT, LuaTarget.Universal].indexOf(
+                target
+            ) >= 0;
+        const numberFormat = useOldFormat ? '*n' : 'n';
+        const lineFormat = useOldFormat ? '*l' : 'l';
+        const lua = tstl(
+            target,
+            `
+          declare const file: LuaFile;
+          const [foo, bar] = file.read("${lineFormat}", "${numberFormat}");
+          declare function takesString(str: string): void;
+          declare function takesNumber(num: number): void;
+          takesString(foo);
+          takesNumber(bar);
+          `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('seek', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            const [pos, err] = file.seek();
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('seek whence', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            const [pos, err] = file.seek("cur");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('seek offset', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            const [pos, err] = file.seek("cur", 1);
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('setvbuf', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            file.setvbuf("no");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('setvbuf with size', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            file.setvbuf("line", 10);
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+
+    test('write', () => {
+        const lua = tstl(
+            target,
+            `
+            declare const file: LuaFile;
+            const [f, err] = file.write("foo", "bar");
+            `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
+});
diff --git a/test/string.spec.ts b/test/string.spec.ts
index 5854b71..e02341a 100644
--- a/test/string.spec.ts
+++ b/test/string.spec.ts
@@ -182,4 +182,15 @@ describeForEachLuaTarget('string', (target) => {
 
         expect(lua).toMatchSnapshot();
     });
+
+    test('string.rep', () => {
+        const lua = tstl(
+            target,
+            `
+            const str = string.rep("foo", 3);
+        `
+        );
+
+        expect(lua).toMatchSnapshot();
+    });
 });