coroutines

10 files changed, 678 insertions, 174 deletions

diff --git a/README.md b/README.md
index f67e193..fd3b3bd 100644
--- a/README.md
+++ b/README.md
@@ -21,65 +21,73 @@
     - [ ] `__tostring`
     - [ ] `__pairs`
 - [ ] C API
-    - [x] lua_version
+    - [x] lua_absindex
     - [x] lua_atpanic
-    - [x] lua_newstate
-    - [x] lua_pushnil
-    - [x] lua_gettop
-    - [x] lua_type
-    - [x] lua_typename
-    - [x] lua_pushboolean
-    - [x] lua_pushinteger
-    - [x] lua_pushnumber
-    - [x] lua_pushlstring
-    - [x] lua_pushstring
-    - [x] lua_pushvalue
-    - [x] lua_tointeger
-    - [x] lua_tointegerx
-    - [x] lua_tolstring
-    - [x] lua_tonumber
-    - [x] lua_tonumberx
-    - [x] lua_toboolean
-    - [x] lua_topointer
-    - [x] lua_pushjsclosure (lua_pushcclosure)
-    - [x] lua_pushjsfunction (lua_pushcfunction)
-    - [x] lua_pop
-    - [x] lua_load
     - [x] lua_call
     - [x] lua_callk
-    - [x] lua_pcall
-    - [x] lua_setglobal
-    - [x] lua_upvalueindex
-    - [x] lua_createtable
-    - [x] lua_newtable
-    - [x] lua_gettable
-    - [x] lua_settable
-    - [x] lua_absindex
     - [x] lua_checkstack
+    - [x] lua_concat
+    - [x] lua_copy
+    - [x] lua_createtable
+    - [x] lua_error
     - [x] lua_getfield
     - [x] lua_getglobal
     - [x] lua_getmetatable
-    - [x] lua_setmetatable
+    - [x] lua_gettable
+    - [x] lua_gettop
+    - [x] lua_insert
+    - [x] lua_isstring
+    - [x] lua_istable
+    - [x] lua_isyieldable
+    - [x] lua_load
+    - [x] lua_newstate
+    - [x] lua_newtable
+    - [x] lua_newthread
+    - [x] lua_next
+    - [x] lua_pcall
+    - [x] lua_pop
+    - [x] lua_pushboolean
     - [x] lua_pushglobaltable
+    - [x] lua_pushinteger
+    - [x] lua_pushjsclosure (lua_pushcclosure)
+    - [x] lua_pushjsfunction (lua_pushcfunction)
     - [x] lua_pushliteral
+    - [x] lua_pushlstring
+    - [x] lua_pushnil
+    - [x] lua_pushnumber
+    - [x] lua_pushstring
+    - [x] lua_pushvalue
+    - [x] lua_rawequal
     - [x] lua_rawget
     - [x] lua_rawgeti
+    - [x] lua_rawlen
     - [x] lua_rawset
-    - [x] lua_setfield
-    - [x] lua_settop
-    - [x] lua_tostring
-    - [x] lua_rawequal
-    - [x] lua_error
-    - [x] lua_concat
-    - [x] lua_isstring
-    - [x] lua_istable
     - [x] lua_remove
+    - [x] lua_resume
     - [x] lua_rotate
-    - [x] lua_insert
+    - [x] lua_setfield
+    - [x] lua_setglobal
+    - [x] lua_setmetatable
+    - [x] lua_settable
+    - [x] lua_settop
+    - [x] lua_status
     - [x] lua_stringtonumber
-    - [x] lua_rawlen
-    - [x] lua_next
-    - [x] lua_copy
+    - [x] lua_toboolean
+    - [x] lua_tointeger
+    - [x] lua_tointegerx
+    - [x] lua_tolstring
+    - [x] lua_tonumber
+    - [x] lua_tonumberx
+    - [x] lua_topointer
+    - [x] lua_tostring
+    - [x] lua_tothread
+    - [x] lua_type
+    - [x] lua_typename
+    - [x] lua_upvalueindex
+    - [x] lua_version
+    - [x] lua_xmove
+    - [x] lua_yield
+    - [x] lua_yieldk
     - [ ] lua_arith
     - [ ] lua_close
     - [ ] lua_compare
@@ -107,9 +115,7 @@
     - [ ] lua_isnumber
     - [ ] lua_isthread
     - [ ] lua_isuserdata
-    - [ ] lua_isyieldable
     - [ ] lua_len
-    - [ ] lua_newthread
     - [ ] lua_newuserdata
     - [ ] lua_numbertointeger
     - [ ] lua_pcallk
@@ -122,44 +128,39 @@
     - [ ] lua_rawsetp
     - [ ] lua_register
     - [ ] lua_replace
-    - [ ] lua_resume
     - [ ] lua_setallocf
     - [ ] lua_sethook
     - [ ] lua_seti
     - [ ] lua_setlocal
     - [ ] lua_setupvalue
     - [ ] lua_setuservalue
-    - [ ] lua_status
     - [ ] lua_tocfunction
-    - [ ] lua_tothread
     - [ ] lua_touserdata
     - [ ] lua_upvalueid
     - [ ] lua_upvaluejoin
-    - [ ] lua_xmove
-    - [ ] lua_yield
-    - [ ] lua_yieldk
 - [ ] Auxiliary library
-    - [x] luaL_newstate
-    - [x] luaL_typename
+    - [x] luaL_argcheck
+    - [x] luaL_argerror
+    - [x] luaL_callmeta
     - [x] luaL_checkany
+    - [x] luaL_checkinteger
+    - [x] luaL_checklstring
+    - [x] luaL_checkstack
     - [x] luaL_checktype
-    - [x] luaL_callmeta
+    - [x] luaL_error
     - [x] luaL_getmetafield
-    - [x] luaL_setfuncs
-    - [x] luaL_checkstack
-    - [x] luaL_tolstring
-    - [x] luaL_openlibs
     - [x] luaL_getsubtable
-    - [x] luaL_requiref
-    - [x] luaL_checkinteger
-    - [x] luaL_checklstring
+    - [x] luaL_newlib
+    - [x] luaL_newstate
+    - [x] luaL_openlibs
     - [x] luaL_opt
     - [x] luaL_optinteger
     - [x] luaL_optlstring
+    - [x] luaL_requiref
+    - [x] luaL_setfuncs
+    - [x] luaL_tolstring
+    - [x] luaL_typename
     - [x] luaL_where
-    - [x] luaL_argerror
-    - [x] luaL_argcheck
-    - [x] luaL_error
     - [ ] luaL_addchar
     - [ ] luaL_addlstring
     - [ ] luaL_addsize
@@ -184,7 +185,6 @@
     - [ ] luaL_loadfile
     - [ ] luaL_loadfilex
     - [ ] luaL_loadstring
-    - [ ] luaL_newlib
     - [ ] luaL_newlibtable
     - [ ] luaL_newmetatable
     - [ ] luaL_optnumber
@@ -200,29 +200,36 @@
     - [ ] luaL_unref
 - [ ] Standard library
     - [ ] Base lib
-        - [x] tostring
-        - [x] print
-        - [x] getmetatable
-        - [x] setmetatable
-        - [x] rawequal
-        - [x] rawset
-        - [x] rawget
-        - [x] type
-        - [x] error
-        - [x] pcall
-        - [x] xpcall
+        - [x] assert
         - [x] collectgarbage (unavailable)
+        - [x] error
+        - [x] getmetatable
         - [x] ipairs
+        - [x] next
         - [x] pairs
+        - [x] pcall
+        - [x] print
+        - [x] rawequal
+        - [x] rawget
+        - [x] rawlen
+        - [x] rawset
         - [x] select
+        - [x] setmetatable
         - [x] tonumber
-        - [x] assert
-        - [x] rawlen
-        - [x] next
+        - [x] tostring
+        - [x] type
+        - [x] xpcall
         - [ ] dofile
         - [ ] loadfile
         - [ ] load
-    - [ ] ...
+    - [ ] Coroutine
+        - [x] coroutine.create
+        - [x] coroutine.resume
+        - [x] coroutine.yield
+        - [ ] coroutine.isyieldable
+        - [ ] coroutine.running
+        - [ ] coroutine.status
+        - [ ] coroutine.wrap
 - [ ] Debug (errors)
 - [ ] DOM API binding
 - [ ] Parse Lua
diff --git a/src/lapi.js b/src/lapi.js
index e9f15c2..2f2802f 100644
--- a/src/lapi.js
+++ b/src/lapi.js
@@ -82,6 +82,19 @@ const lua_checkstack = function(L, n) {
     return L.stack.length < luaconf.LUAI_MAXSTACK;
 };
 
+const lua_xmove = function(from, to, n) {
+    if (from === to) return;
+    assert(n < (from.top - from.ci.funcOff), "not enough elements in the stack");
+    assert(from.l_G === to.l_G, "moving among independent states");
+    assert(to.ci.top - to.top >= n, "stack overflow");
+
+    from.top -= n;
+    for (let i = 0; i < n; i++) {
+        to.stack[to.top] = from.stack[from.top + i];
+        to.top++;
+    }
+};
+
 /*
 ** basic stack manipulation
 */
@@ -490,6 +503,11 @@ const lua_tonumber = function(L, idx) {
     return lvm.tonumber(index2addr(L, idx))
 };
 
+const lua_tothread = function(L, idx) {
+    let o = index2addr(L, idx);
+    return o.ttisthread() ? o.value : null;
+};
+
 const lua_topointer = function(L, idx) {
     let o = index2addr(L, idx);
     switch (o.ttype()) {
@@ -564,8 +582,12 @@ const lua_load = function(L, data, chunckname) {
     return status;
 };
 
+const lua_status = function(L) {
+    return L.status;
+};
+
 const lua_callk = function(L, nargs, nresults, ctx, k) {
-    assert(k === null || !(L.ci.callstatus & CIST_LUA), "cannot use continuations inside hooks");
+    assert(k === null || !(L.ci.callstatus & lstate.CIST_LUA), "cannot use continuations inside hooks");
     assert(nargs + 1 < L.top - L.ci.funcOff, "not enough elements in the stack");
     assert(L.status === TS.LUA_OK, "cannot do calls on non-normal thread");
     assert(nargs === lua.LUA_MULTRET || (L.ci.top - L.top >= nargs - nresults, "results from function overflow current stack size"));
@@ -640,7 +662,6 @@ const lua_pcall = function(L, n, r, f) {
     return lua_pcallk(L, n, r, f, 0, null);
 };
 
-
 /*
 ** miscellaneous functions
 */
@@ -685,66 +706,69 @@ const lua_getextraspace = function () {
     return null;
 };
 
-module.exports.lua_pushvalue       = lua_pushvalue;
-module.exports.lua_pushnil         = lua_pushnil;
-module.exports.lua_pushnumber      = lua_pushnumber;
-module.exports.lua_pushinteger     = lua_pushinteger;
-module.exports.lua_pushlstring     = lua_pushlstring;
-module.exports.lua_pushstring      = lua_pushstring;
-module.exports.lua_pushliteral     = lua_pushliteral;
-module.exports.lua_pushboolean     = lua_pushboolean;
-module.exports.lua_pushcclosure    = lua_pushcclosure;
-module.exports.lua_pushcfunction   = lua_pushcfunction;
-module.exports.lua_pushjsclosure   = lua_pushjsclosure;
-module.exports.lua_pushjsfunction  = lua_pushjsfunction;
-module.exports.lua_version         = lua_version;
+module.exports.index2addr          = index2addr;
+module.exports.lua_absindex        = lua_absindex;
 module.exports.lua_atpanic         = lua_atpanic;
+module.exports.lua_call            = lua_call;
+module.exports.lua_callk           = lua_callk;
+module.exports.lua_checkstack      = lua_checkstack;
+module.exports.lua_concat          = lua_concat;
+module.exports.lua_copy            = lua_copy;
+module.exports.lua_createtable     = lua_createtable;
+module.exports.lua_error           = lua_error;
+module.exports.lua_gc              = lua_gc;
+module.exports.lua_getallocf       = lua_getallocf;
+module.exports.lua_getextraspace   = lua_getextraspace;
+module.exports.lua_getfield        = lua_getfield;
+module.exports.lua_getglobal       = lua_getglobal;
+module.exports.lua_geti            = lua_geti;
+module.exports.lua_getmetatable    = lua_getmetatable;
+module.exports.lua_gettable        = lua_gettable;
 module.exports.lua_gettop          = lua_gettop;
-module.exports.lua_typename        = lua_typename;
-module.exports.lua_type            = lua_type;
-module.exports.lua_tonumber        = lua_tonumber;
-module.exports.lua_tointeger       = lua_tointeger;
-module.exports.lua_toboolean       = lua_toboolean;
-module.exports.lua_tolstring       = lua_tolstring;
-module.exports.lua_tostring        = lua_tostring;
-module.exports.lua_topointer       = lua_topointer;
+module.exports.lua_insert          = lua_insert;
+module.exports.lua_isstring        = lua_isstring;
+module.exports.lua_istable         = lua_istable;
 module.exports.lua_load            = lua_load;
-module.exports.lua_callk           = lua_callk;
-module.exports.lua_call            = lua_call;
-module.exports.lua_pcallk          = lua_pcallk;
+module.exports.lua_newtable        = lua_newtable;
+module.exports.lua_next            = lua_next;
 module.exports.lua_pcall           = lua_pcall;
+module.exports.lua_pcallk          = lua_pcallk;
 module.exports.lua_pop             = lua_pop;
-module.exports.lua_setglobal       = lua_setglobal;
-module.exports.lua_istable         = lua_istable;
-module.exports.lua_createtable     = lua_createtable;
-module.exports.lua_newtable        = lua_newtable;
-module.exports.lua_settable        = lua_settable;
-module.exports.lua_gettable        = lua_gettable;
-module.exports.lua_geti            = lua_geti;
-module.exports.lua_absindex        = lua_absindex;
-module.exports.index2addr          = index2addr;
+module.exports.lua_pushboolean     = lua_pushboolean;
+module.exports.lua_pushcclosure    = lua_pushcclosure;
+module.exports.lua_pushcfunction   = lua_pushcfunction;
+module.exports.lua_pushglobaltable = lua_pushglobaltable;
+module.exports.lua_pushinteger     = lua_pushinteger;
+module.exports.lua_pushjsclosure   = lua_pushjsclosure;
+module.exports.lua_pushjsfunction  = lua_pushjsfunction;
+module.exports.lua_pushliteral     = lua_pushliteral;
+module.exports.lua_pushlstring     = lua_pushlstring;
+module.exports.lua_pushnil         = lua_pushnil;
+module.exports.lua_pushnumber      = lua_pushnumber;
+module.exports.lua_pushstring      = lua_pushstring;
+module.exports.lua_pushvalue       = lua_pushvalue;
+module.exports.lua_rawequal        = lua_rawequal;
 module.exports.lua_rawget          = lua_rawget;
-module.exports.lua_rawset          = lua_rawset;
+module.exports.lua_rawgeti         = lua_rawgeti;
 module.exports.lua_rawlen          = lua_rawlen;
-module.exports.lua_isstring        = lua_isstring;
-module.exports.lua_rotate          = lua_rotate;
+module.exports.lua_rawset          = lua_rawset;
 module.exports.lua_remove          = lua_remove;
-module.exports.lua_checkstack      = lua_checkstack;
-module.exports.lua_rawgeti         = lua_rawgeti;
-module.exports.lua_pushglobaltable = lua_pushglobaltable;
+module.exports.lua_rotate          = lua_rotate;
 module.exports.lua_setfield        = lua_setfield;
-module.exports.lua_getfield        = lua_getfield;
-module.exports.lua_getglobal       = lua_getglobal;
-module.exports.lua_getmetatable    = lua_getmetatable;
+module.exports.lua_setglobal       = lua_setglobal;
 module.exports.lua_setmetatable    = lua_setmetatable;
+module.exports.lua_settable        = lua_settable;
 module.exports.lua_settop          = lua_settop;
-module.exports.lua_rawequal        = lua_rawequal;
-module.exports.lua_concat          = lua_concat;
-module.exports.lua_error           = lua_error;
-module.exports.lua_insert          = lua_insert;
-module.exports.lua_gc              = lua_gc;
-module.exports.lua_getallocf       = lua_getallocf;
-module.exports.lua_getextraspace   = lua_getextraspace;
+module.exports.lua_status          = lua_status;
 module.exports.lua_stringtonumber  = lua_stringtonumber;
-module.exports.lua_copy            = lua_copy;
-module.exports.lua_next            = lua_next;
\ No newline at end of file
+module.exports.lua_toboolean       = lua_toboolean;
+module.exports.lua_tointeger       = lua_tointeger;
+module.exports.lua_tolstring       = lua_tolstring;
+module.exports.lua_tonumber        = lua_tonumber;
+module.exports.lua_topointer       = lua_topointer;
+module.exports.lua_tostring        = lua_tostring;
+module.exports.lua_tothread        = lua_tothread;
+module.exports.lua_type            = lua_type;
+module.exports.lua_typename        = lua_typename;
+module.exports.lua_version         = lua_version;
+module.exports.lua_xmove           = lua_xmove;
\ No newline at end of file
diff --git a/src/lauxlib.js b/src/lauxlib.js
index 29b223f..a04f3be 100644
--- a/src/lauxlib.js
+++ b/src/lauxlib.js
@@ -310,6 +310,11 @@ const luaL_checkstack = function(L, space, msg) {
     }
 };
 
+const luaL_newlib = function(L, l) {
+    lapi.lua_createtable(L);
+    luaL_setfuncs(L, l, 0);
+};
+
 module.exports.luaL_newstate     = luaL_newstate;
 module.exports.luaL_typename     = luaL_typename;
 module.exports.luaL_checkany     = luaL_checkany;
@@ -331,4 +336,5 @@ module.exports.luaL_optinteger   = luaL_optinteger;
 module.exports.luaL_opt          = luaL_opt;
 module.exports.luaL_where        = luaL_where;
 module.exports.luaL_error        = luaL_error;
-module.exports.luaL_argerror     = luaL_argerror;
\ No newline at end of file
+module.exports.luaL_argerror     = luaL_argerror;
+module.exports.luaL_newlib       = luaL_newlib;
\ No newline at end of file
diff --git a/src/lcorolib.js b/src/lcorolib.js
new file mode 100644
index 0000000..73699a7
--- /dev/null
+++ b/src/lcorolib.js
@@ -0,0 +1,86 @@
+/* jshint esversion: 6 */
+"use strict";
+
+const assert  = require('assert');
+
+const lua     = require('./lua.js');
+const lapi    = require('./lapi.js');
+const lauxlib = require('./lauxlib.js');
+const lstate  = require('./lstate.js');
+const ldo     = require('./ldo.js');
+const CT      = lua.constant_types;
+const TS      = lua.thread_status;
+
+const getco = function(L) {
+    let co = lapi.lua_tothread(L, 1);
+    lauxlib.luaL_argcheck(L, co, 1, "thread expected");
+    return co;
+};
+
+const auxresume = function(L, co, narg) {
+    if (!lapi.lua_checkstack(co, narg)) {
+        lapi.lua_pushliteral(L, "too many arguments to resume");
+        return -1;  /* error flag */
+    }
+
+    if (lapi.lua_status(co) === TS.LUA_OK && lapi.lua_gettop(co) === 0) {
+        lapi.lua_pushliteral(L, "cannot resume dead coroutine");
+        return -1;  /* error flag */
+    }
+
+    lapi.lua_xmove(L, co, narg);
+    let status = ldo.lua_resume(co, L, narg);
+    if (status === TS.LUA_OK || status === TS.LUA_YIELD) {
+        let nres = lapi.lua_gettop(L);
+        if (!lapi.lua_checkstack(L, nres + 1)) {
+            lapi.lua_pop(co, nres);  /* remove results anyway */
+            lapi.lua_pushliteral(L, "too many results to resume");
+            return -1;  /* error flag */
+        }
+
+        lapi.lua_xmove(co,  L, nres);  /* move yielded values */
+        return nres;
+    } else {
+        lapi.lua_xmove(co, L, 1);  /* move error message */
+        return -1;  /* error flag */
+    }
+};
+
+const luaB_resume = function(L) {
+    let co = getco(L);
+    let r = auxresume(L, co, lapi.lua_gettop(L) - 1);
+    if (r < 0) {
+        lapi.lua_pushboolean(L, 0);
+        lapi.lua_insert(L, -2);
+        return 2;  /* return false + error message */
+    } else {
+        lapi.lua_pushboolean(L, 1);
+        lapi.lua_insert(L, -(r + 1));
+        return r + 1;  /* return true + 'resume' returns */
+    }
+};
+
+const luaB_cocreate = function(L) {
+    lauxlib.luaL_checktype(L, 1, CT.LUA_TFUNCTION);
+    let NL = lstate.lua_newthread(L);
+    lapi.lua_pushvalue(L, 1);  /* move function to top */
+    lapi.lua_xmove(L, NL, 1);  /* move function from L to NL */
+    return 1;
+};
+
+const luaB_yield = function(L) {
+    return ldo.lua_yield(L, lapi.lua_gettop(L));
+};
+
+const co_funcs = {
+    "create":  luaB_cocreate,
+    "yield":   luaB_yield,
+    "resume":  luaB_resume
+};
+
+const luaopen_coroutine = function(L) {
+    lauxlib.luaL_newlib(L, co_funcs);
+    return 1;
+};
+
+module.exports.luaopen_coroutine = luaopen_coroutine;
\ No newline at end of file
diff --git a/src/ldo.js b/src/ldo.js
index 4333f5e..8d12c9f 100644
--- a/src/ldo.js
+++ b/src/ldo.js
@@ -27,6 +27,7 @@ const seterrorobj = function(L, errcode, oldtop) {
         }
         case TS.LUA_ERRERR: {
             L.stack[oldtop] = new TValue(CT.LUA_TLNGSTR, "error in error handling");
+            break;
         }
         default: {
             L.stack[oldtop] = L.stack[L.top - 1];
@@ -79,7 +80,6 @@ const luaD_precall = function(L, off, nresults) {
             luaD_poscall(L, ci, L.top - n, n);
 
             return true;
-            break;
         }
         case CT.LUA_TLCL: {
             let p = func.p;
@@ -260,7 +260,7 @@ const luaD_rawrunprotected = function(L, f, ud) {
     try {
         f(L, ud);
     } catch (e) {
-        if (lj.status == 0) lj.status = -1;
+        if (lj.status === 0) lj.status = -1;
     }
 
     L.errorJmp = lj.previous;
@@ -270,6 +270,209 @@ const luaD_rawrunprotected = function(L, f, ud) {
 
 };
 
+/*
+** Completes the execution of an interrupted C function, calling its
+** continuation function.
+*/
+const finishCcall = function(L, status) {
+    let ci = L.ci;
+
+    /* must have a continuation and must be able to call it */
+    assert(ci.u.c.k !== null && L.nny === 0);
+    /* error status can only happen in a protected call */
+    assert(ci.callstatus & lstate.CIST_YPCALL || status === TS.LUA_YIELD);
+
+    if (ci.callstatus & TS.CIST_YPCALL) {  /* was inside a pcall? */
+        ci.callstatus &= ~TS.CIST_YPCALL;  /* continuation is also inside it */
+        L.errfunc = ci.u.c.old_errfunc;  /* with the same error function */
+    }
+
+    /* finish 'lua_callk'/'lua_pcall'; CIST_YPCALL and 'errfunc' already
+       handled */
+    if (ci.nresults === LUA_MULTRET && L.ci.top < L.top) L.ci.top = L.top;
+    let n = ci.u.c.k(L, status, ci.u.c.ctx);  /* call continuation function */
+    assert(n < (L.top - L.ci.funcOff), "not enough elements in the stack");
+    luaD_poscall(L, ci, L.top - n, n);  /* finish 'luaD_precall' */
+};
+
+/*
+** Executes "full continuation" (everything in the stack) of a
+** previously interrupted coroutine until the stack is empty (or another
+** interruption long-jumps out of the loop). If the coroutine is
+** recovering from an error, 'ud' points to the error status, which must
+** be passed to the first continuation function (otherwise the default
+** status is LUA_YIELD).
+*/
+const unroll = function(L, ud) {
+    if (ud !== null)  /* error status? */
+        finishCcall(L, ud);  /* finish 'lua_pcallk' callee */
+
+    while (L.ci !== L.base_ci) {  /* something in the stack */
+        if (!(L.ci.callstatus & lstate.CIST_LUA))  /* C function? */
+            finishCcall(L, lstate.LUA_YIELD);  /* complete its execution */
+        else {  /* Lua function */
+            lvm.luaV_finishOp(L);  /* finish interrupted instruction */
+            lvm.luaV_execute(L);  /* execute down to higher C 'boundary' */
+        }
+    }
+};
+
+/*
+** Try to find a suspended protected call (a "recover point") for the
+** given thread.
+*/
+const findpcall = function(L) {
+    for (let ci = L.ci; ci !== null; ci = ci.previous) {  /* search for a pcall */
+        if (ci.callstatus & lstate.CIST_YPCALL)
+            return ci;
+    }
+
+    return null;  /* no pending pcall */
+};
+
+/*
+** Recovers from an error in a coroutine. Finds a recover point (if
+** there is one) and completes the execution of the interrupted
+** 'luaD_pcall'. If there is no recover point, returns zero.
+*/
+const recover = function(L, status) {
+    let ci = findpcall(L);
+    if (ci === null) return 0;  /* no recovery point */
+    /* "finish" luaD_pcall */
+    let oldtop = L.stack[ci.extra];
+    lfunc.luaF_close(L, oldtop);
+    seterrorobj(L, status, oldtop);
+    L.ci = ci;
+    L.allowhook = ci.callstatus & lstate.CIST_OAH;  /* restore original 'allowhook' */
+    L.nny = 0;  /* should be zero to be yieldable */
+    L.errfunc = ci.u.c.old_errfunc;
+    return 1;  /* continue running the coroutine */
+};
+
+/*
+** Signal an error in the call to 'lua_resume', not in the execution
+** of the coroutine itself. (Such errors should not be handled by any
+** coroutine error handler and should not kill the coroutine.)
+*/
+const resume_error = function(L, msg, narg) {
+    L.top -= narg;  /* remove args from the stack */
+    L.stack[L.top++] = new TValue(CT.LUA_TLNGSTR, msg);  /* push error message */
+    assert(L.top <= L.ci.top, "stack overflow");
+    return TS.LUA_ERRRUN;
+};
+
+/*
+** Do the work for 'lua_resume' in protected mode. Most of the work
+** depends on the status of the coroutine: initial state, suspended
+** inside a hook, or regularly suspended (optionally with a continuation
+** function), plus erroneous cases: non-suspended coroutine or dead
+** coroutine.
+*/
+const resume = function(L, n) {
+    let firstArg = L.top - n;  /* first argument */
+    let ci = L.ci;
+    if (L.status === TS.LUA_OK) {  /* starting a coroutine? */
+        if (!luaD_precall(L, firstArg - 1, lua.LUA_MULTRET))  /* Lua function? */
+            lvm.luaV_execute(L);  /* call it */
+    } else {  /* resuming from previous yield */
+        assert(L.status === TS.LUA_YIELD);
+        L.status = TS.LUA_OK;  /* mark that it is running (again) */
+        ci.funcOff = ci.extra;
+        ci.func = L.stack[ci.funcOff];
+
+        if (ci.callstatus & lstate.CIST_LUA)  /* yielded inside a hook? */
+            lvm.luaV_execute(L);  /* just continue running Lua code */
+        else {  /* 'common' yield */
+            if (ci.u.c.k !== null) {  /* does it have a continuation function? */
+                n = ci.u.c.k(L, TS.LUA_YIELD, ci.u.c.ctx); /* call continuation */
+                assert(n < (L.top - L.ci.funcOff), "not enough elements in the stack");
+                firstArg = L.top - n;  /* yield results come from continuation */
+            }
+
+            luaD_poscall(L, ci, firstArg, n);  /* finish 'luaD_precall' */
+        }
+
+        unroll(L, null);  /* run continuation */
+    }
+};
+
+const lua_resume = function(L, from, nargs) {
+    let oldnny = L.nny;  /* save "number of non-yieldable" calls */
+
+    if (L.status === TS.LUA_OK) {  /* may be starting a coroutine */
+        if (L.ci !== L.base_ci)  /* not in base level? */
+            return resume_error(L, "cannot resume non-suspended coroutine", nargs);
+    } else if (L.status !== TS.LUA_YIELD)
+        return resume_error(L, "cannot resume dead coroutine", nargs);
+
+    L.nCcalls = from ? from.nCcalls + 1 : 1;
+    if (L.nCcalls >= llimit.LUAI_MAXCCALLS)
+        return resume_error(L, "JS stack overflow", nargs);
+
+    L.nny = 0;  /* allow yields */
+
+    assert((L.status === TS.LUA_OK ? nargs + 1: nargs) < (L.top - L.ci.funcOff),
+        "not enough elements in the stack");
+
+    let status = luaD_rawrunprotected(L, resume, nargs);
+    if (status === -1)  /* error calling 'lua_resume'? */
+        status = TS.LUA_ERRRUN;
+    else {  /* continue running after recoverable errors */
+        while (status > TS.LUA_YIELD && recover(L, status)) {
+            /* unroll continuation */
+            status = luaD_rawrunprotected(L, unroll, status);
+        }
+
+        if (status > TS.LUA_YIELD) {  /* unrecoverable error? */
+            L.status = status;  /* mark thread as 'dead' */
+            seterrorobj(L, status, L.top);  /* push error message */
+            L.ci.top = L.top;
+        } else
+            assert(status === L.status);  /* normal end or yield */
+    }
+
+    L.nny = oldnny;  /* restore 'nny' */
+    L.nCcalls--;
+    assert(L.nCcalls === (from ? from.nCcalls : 0));
+    return status;
+};
+
+const lua_isyieldable = function(L) {
+    return L.nny === 0;
+};
+
+const lua_yieldk = function(L, nresults, ctx, k) {
+    let ci = L.ci;
+    assert(nresults < (L.top - L.ci.funcOff), "not enough elements in the stack");
+
+    if (L.nny > 0) {
+        if (L !== L.l_G.mainthread)
+            ldebug.luaG_runerror(L, "attempt to yield across a JS-call boundary");
+        else
+            ldebug.luaG_runerror(L, "attempt to yield from outside a coroutine");
+    }
+
+    L.status = TS.LUA_YIELD;
+    ci.extra = ci.funcOff;  /* save current 'func' */
+    if (ci.callstatus & lstate.CIST_LUA)  /* inside a hook? */
+        assert(k === null, "hooks cannot continue after yielding");
+    else {
+        ci.u.c.k = k;
+        if (k !== null)  /* is there a continuation? */
+            ci.u.c.ctx = ctx;  /* save context */
+        ci.funcOff = L.top - nresults - 1;  /* protect stack below results */
+        ci.func = L.stack[ci.funcOff];
+        luaD_throw(L, TS.LUA_YIELD);
+    }
+
+    assert(ci.callstatus & lstate.CIST_HOOKED);  /* must be inside a hook */
+    return 0;  /* return to 'luaD_hook' */
+};
+
+const lua_yield = function(L, n) {
+    lua_yieldk(L, n, 0, null);
+};
+
 const luaD_pcall = function(L, func, u, old_top, ef) {
     let old_ci = L.ci;
     // TODO: lu_byte old_allowhooks = L->allowhook;
@@ -321,16 +524,20 @@ const luaD_protectedparser = function(L, data, name) {
     return status;
 };
 
-module.exports.nil                  = nil;
-module.exports.luaD_precall         = luaD_precall;
-module.exports.luaD_poscall         = luaD_poscall;
-module.exports.moveresults          = moveresults;
 module.exports.adjust_varargs       = adjust_varargs;
-module.exports.tryfuncTM            = tryfuncTM;
-module.exports.stackerror           = stackerror;
+module.exports.lua_isyieldable      = lua_isyieldable;
+module.exports.lua_resume           = lua_resume;
+module.exports.lua_yield            = lua_yield;
+module.exports.lua_yieldk           = lua_yieldk;
 module.exports.luaD_call            = luaD_call;
 module.exports.luaD_callnoyield     = luaD_callnoyield;
 module.exports.luaD_pcall           = luaD_pcall;
-module.exports.luaD_throw           = luaD_throw;
+module.exports.luaD_poscall         = luaD_poscall;
+module.exports.luaD_precall         = luaD_precall;
+module.exports.luaD_protectedparser = luaD_protectedparser;
 module.exports.luaD_rawrunprotected = luaD_rawrunprotected;
-module.exports.luaD_protectedparser = luaD_protectedparser;
\ No newline at end of file
+module.exports.luaD_throw           = luaD_throw;
+module.exports.moveresults          = moveresults;
+module.exports.nil                  = nil;
+module.exports.stackerror           = stackerror;
+module.exports.tryfuncTM            = tryfuncTM;
\ No newline at end of file
diff --git a/src/linit.js b/src/linit.js
index fc2a54d..d52b640 100644
--- a/src/linit.js
+++ b/src/linit.js
@@ -5,10 +5,13 @@ const assert = require('assert');
 
 const lapi     = require('./lapi.js');
 const lauxlib  = require('./lauxlib.js');
+const lualib   = require('./lualib.js');
 const lbaselib = require('./lbaselib.js');
+const lcorolib = require('./lcorolib.js');
 
 const loadedlibs = {
-    "_G": lbaselib.luaopen_base
+    [lualib.LUA_COLIBNAME]: lcorolib.luaopen_coroutine,
+    "_G":                  lbaselib.luaopen_base
 };
 
 const luaL_openlibs = function(L) {
diff --git a/src/lstate.js b/src/lstate.js
index eec9fae..9a9c9e0 100644
--- a/src/lstate.js
+++ b/src/lstate.js
@@ -1,8 +1,10 @@
 /*jshint esversion: 6 */
 "use strict";
 
+const assert               = require('assert');
+
 const lua                  = require('./lua.js');
-const Table                = require('./lobject.js').Table;
+const lobject              = require('./lobject.js');
 const ldo                  = require('./ldo.js');
 const lapi                 = require('./lapi.js');
 const nil                  = ldo.nil;
@@ -41,9 +43,10 @@ class CallInfo {
 
 }
 
-class lua_State {
+class lua_State extends lobject.TValue {
 
-    constructor(cl) {
+    constructor() {
+        super(CT.LUA_TTHREAD, null);
         this.base_ci = new CallInfo(); // Will be populated later
         this.top = 0;
         this.ci = null;
@@ -52,12 +55,12 @@ class lua_State {
         this.openupval = [];
         this.status = TS.LUA_OK;
         this.next = null;
-        this.tt = CT.LUA_TTHREAD;
         this.twups = [this];
         this.errorJmp = null;
-        // TODO: hooks
         this.nny = 1;
         this.errfunc = 0;
+
+        this.value = this;
     }
 
 }
@@ -94,10 +97,10 @@ const stack_init = function(L1, L) {
 ** Create registry table and its predefined values
 */
 const init_registry = function(L, g) {
-    let registry = new Table();
+    let registry = new lobject.Table();
     g.l_registry = registry;
     registry.value.set(lua.LUA_RIDX_MAINTHREAD - 1, L);
-    registry.value.set(lua.LUA_RIDX_GLOBALS - 1, new Table());
+    registry.value.set(lua.LUA_RIDX_GLOBALS - 1, new lobject.Table());
 };
 
 /*
@@ -113,11 +116,44 @@ const f_luaopen = function(L) {
     g.version = lapi.lua_version(null);
 };
 
+const preinit_thread = function(L, g) {
+    L.l_G = g;
+    L.stack = [];
+    L.ci = null;
+    L.nci = 0;
+    L.twups = [L];  /* thread has no upvalues */
+    L.errorJmp = null;
+    L.nCcalls = 0;
+    L.hook = null;
+    L.hookmask = 0;
+    L.basehookcount = 0;
+    L.allowhook = 1;
+    L.hookcount = L.basehookcount;
+    L.openupval = [];
+    L.nny = 1;
+    L.status = TS.LUA_OK;
+    L.errfunc = 0;
+};
+
+const lua_newthread = function(L) {
+    let g = L.l_G;
+    let L1 = new lua_State();
+    L.stack[L.top++] = L1;
+    assert(L.top <= L.ci.top, "stack overflow");
+    preinit_thread(L1, g);
+    L1.hookmask = L.hookmask;
+    L1.basehookcount = L.basehookcount;
+    L1.hook = L.hook;
+    L1.hookcount = L1.basehookcount;
+    stack_init(L1, L);
+    return L1;
+};
+
 const lua_newstate = function() {
     let L = new lua_State();
     let g = new global_State(L);
 
-    L.l_G = g;
+    preinit_thread(L, g);
 
     if (luaD_rawrunprotected(L, f_luaopen, null) !== TS.LUA_OK) {
         L = null;
@@ -137,4 +173,5 @@ module.exports.CIST_TAIL      = (1<<5);  /* call was tail called */
 module.exports.CIST_HOOKYIELD = (1<<6);  /* last hook called yielded */
 module.exports.CIST_LEQ       = (1<<7);  /* using __lt for __le */
 module.exports.CIST_FIN       = (1<<8);   /* call is running a finalizer */
-module.exports.lua_newstate   = lua_newstate;
\ No newline at end of file
+module.exports.lua_newstate   = lua_newstate;
+module.exports.lua_newthread  = lua_newthread;
\ No newline at end of file
diff --git a/src/lualib.js b/src/lualib.js
index 1eff812..d87cfbc 100644
--- a/src/lualib.js
+++ b/src/lualib.js
@@ -7,5 +7,26 @@ const lua    = require('./lua.js');
 
 const LUA_VERSUFFIX = "_" + lua.LUA_VERSION_MAJOR + "_" + lua.LUA_VERSION_MINOR;
 
+const LUA_COLIBNAME   = "coroutine";
+const LUA_TABLIBNAME  = "table"
+const LUA_IOLIBNAME   = "io"
+const LUA_OSLIBNAME   = "os"
+const LUA_STRLIBNAME  = "string"
+const LUA_UTF8LIBNAME = "utf8"
+const LUA_BITLIBNAME  = "bit32"
+const LUA_MATHLIBNAME = "math"
+const LUA_DBLIBNAME   = "debug"
+const LUA_LOADLIBNAME = "package"
 
-module.exports.LUA_VERSUFFIX = LUA_VERSUFFIX;
\ No newline at end of file
+
+module.exports.LUA_BITLIBNAME  = LUA_BITLIBNAME;
+module.exports.LUA_COLIBNAME   = LUA_COLIBNAME;
+module.exports.LUA_DBLIBNAME   = LUA_DBLIBNAME;
+module.exports.LUA_IOLIBNAME   = LUA_IOLIBNAME;
+module.exports.LUA_LOADLIBNAME = LUA_LOADLIBNAME;
+module.exports.LUA_MATHLIBNAME = LUA_MATHLIBNAME;
+module.exports.LUA_OSLIBNAME   = LUA_OSLIBNAME;
+module.exports.LUA_STRLIBNAME  = LUA_STRLIBNAME;
+module.exports.LUA_TABLIBNAME  = LUA_TABLIBNAME;
+module.exports.LUA_UTF8LIBNAME = LUA_UTF8LIBNAME;
+module.exports.LUA_VERSUFFIX   = LUA_VERSUFFIX;
\ No newline at end of file
diff --git a/src/lvm.js b/src/lvm.js
index a31e0c7..15a11e4 100644
--- a/src/lvm.js
+++ b/src/lvm.js
@@ -22,6 +22,65 @@ const ltm            = require('./ltm.js');
 const ltable         = require('./ltable.js');
 const ldebug         = require('./ldebug.js');
 
+/*
+** finish execution of an opcode interrupted by an yield
+*/
+const luaV_finishOp = function(L) {
+    let ci = L.ci;
+    let base = ci.u.l.base;
+    let inst = ci.u.l.savedpc[ci.pcOff - 1];  /* interrupted instruction */
+    let op = OC.OpCodes[inst.opcode];
+
+    switch (op) {  /* finish its execution */
+        case "OP_ADD": case "OP_SUB": case "OP_MUL": case "OP_DIV": case "OP_IDIV":
+        case "OP_BAND": case "OP_BOR": case "OP_BXOR": case "OP_SHL": case "OP_SHR":
+        case "OP_MOD": case "OP_POW":
+        case "OP_UNM": case "OP_BNOT": case "OP_LEN":
+        case "OP_GETTABUP": case "OP_GETTABLE": case "OP_SELF": {
+            L.stack[base + inst.A] = L.stack[--L.top];
+            break;
+        }
+        case "OP_LE": case "OP_LT": case "OP_EQ": {
+            let res = !L.stack[L.top - 1].l_isfalse();
+            L.top--;
+            if (ci.callstatus & lstate.CIST_LEQ) {  /* "<=" using "<" instead? */
+                assert(op === "OP_LE");
+                ci.callstatus ^= lstate.CIST_LEQ;  /* clear mark */
+                res = res !== 1 ? 1 : 0;  /* negate result */
+            }
+            assert(OC.OpCodes[ci.u.l.savedpc[ci.pcOff]] === "OP_JMP");
+            if (res !== inst.A)  /* condition failed? */
+                ci.pcOff++;  /* skip jump instruction */
+            break;
+        }
+        case "OP_CONCAT": {
+            let top = L.top - 1;  /* top when 'luaT_trybinTM' was called */
+            let b = inst.B;  /* first element to concatenate */
+            let total = top - 1 - (base + b);  /* yet to concatenate */
+            L.stack[L.top - 2] = L.stack[top];  /* put TM result in proper position */
+            if (total > 1) {  /* are there elements to concat? */
+                L.top = top - 1;  /* top is one after last element (at top-2) */
+                luaV_concat(L, total);  /* concat them (may yield again) */
+            }
+
+            /* move final result to final position */
+            L.stack[ci.u.l.base + inst.A] = L.stack[L.top - 1];
+            L.top = ci.top;  /* restore top */
+            break;
+        }
+        case "OP_TFORCALL": {
+            assert(OC.OpCodes[ci.u.l.savedpc[ci.pcOff]] === "OP_TFORLOOP");
+            L.top = ci.top;  /* correct top */
+            break;
+        }
+        case "OP_CALL": {
+            if (inst.C - 1 >= 0)  /* nresults >= 0? */
+                L.top = ci.top;  /* adjust results */
+            break;
+        }
+    }
+};
+
 const RA = function(L, base, i) {
    return base + i.A;
 };
@@ -1013,28 +1072,29 @@ const luaV_finishset = function(L, t, key, val, slot, recur) {
 }
 
 
-module.exports.RA             = RA;
-module.exports.RB             = RB;
-module.exports.RC             = RC;
-module.exports.RKB            = RKB;
-module.exports.RKC            = RKC;
-module.exports.luaV_execute   = luaV_execute;
 module.exports.dojump         = dojump;
 module.exports.donextjump     = donextjump;
-module.exports.luaV_lessequal = luaV_lessequal;
-module.exports.luaV_lessthan  = luaV_lessthan;
-module.exports.luaV_equalobj  = luaV_equalobj;
 module.exports.forlimit       = forlimit;
-module.exports.luaV_tointeger = luaV_tointeger;
-module.exports.tonumber       = tonumber;
-module.exports.tointeger      = tointeger;
-module.exports.LTnum          = LTnum;
-module.exports.LEnum          = LEnum;
+module.exports.gettable       = gettable;
+module.exports.l_strcmp       = l_strcmp;
 module.exports.LEintfloat     = LEintfloat;
+module.exports.LEnum          = LEnum;
 module.exports.LTintfloat     = LTintfloat;
-module.exports.l_strcmp       = l_strcmp;
-module.exports.luaV_objlen    = luaV_objlen;
+module.exports.LTnum          = LTnum;
+module.exports.luaV_concat    = luaV_concat;
+module.exports.luaV_equalobj  = luaV_equalobj;
+module.exports.luaV_execute   = luaV_execute;
+module.exports.luaV_finishOp  = luaV_finishOp;
 module.exports.luaV_finishset = luaV_finishset;
-module.exports.gettable       = gettable;
+module.exports.luaV_lessequal = luaV_lessequal;
+module.exports.luaV_lessthan  = luaV_lessthan;
+module.exports.luaV_objlen    = luaV_objlen;
+module.exports.luaV_tointeger = luaV_tointeger;
+module.exports.RA             = RA;
+module.exports.RB             = RB;
+module.exports.RC             = RC;
+module.exports.RKB            = RKB;
+module.exports.RKC            = RKC;
 module.exports.settable       = settable;
-module.exports.luaV_concat    = luaV_concat;
\ No newline at end of file
+module.exports.tointeger      = tointeger;
+module.exports.tonumber       = tonumber;
\ No newline at end of file
diff --git a/tests/lcorolib.js b/tests/lcorolib.js
new file mode 100644
index 0000000..6b48912
--- /dev/null
+++ b/tests/lcorolib.js
@@ -0,0 +1,53 @@
+/*jshint esversion: 6 */
+"use strict";
+
+const test       = require('tape');
+const beautify   = require('js-beautify').js_beautify;
+
+const tests      = require("./tests.js");
+const getState   = tests.getState;
+const toByteCode = tests.toByteCode;
+
+const VM         = require("../src/lvm.js");
+const ldo        = require("../src/ldo.js");
+const lapi       = require("../src/lapi.js");
+const lauxlib    = require("../src/lauxlib.js");
+const lua        = require('../src/lua.js');
+const linit      = require('../src/linit.js');
+const CT         = lua.constant_types;
+
+test('simple coroutine', function (t) {
+    let luaCode = `
+        local co = coroutine.create(function (start)
+            local b = coroutine.yield(start * start);
+            coroutine.yield(b * b)
+        end)
+
+        local success, pow = coroutine.resume(co, 5)
+        success, pow = coroutine.resume(co, pow)
+
+        return pow
+    `, L;
+    
+    t.plan(2);
+
+    t.doesNotThrow(function () {
+
+        let bc = toByteCode(luaCode).dataView;
+
+        L = lauxlib.luaL_newstate();
+
+        linit.luaL_openlibs(L);
+
+        lapi.lua_load(L, bc, "test-coroutine");
+
+        lapi.lua_call(L, 0, -1);
+
+    }, "JS Lua program ran without error");
+
+    t.strictEqual(
+        lapi.lua_tonumber(L, -1),
+        625,
+        "Correct element(s) on the stack"
+    );
+});
\ No newline at end of file