Re: Packaging and importing

[Rici Lake <lua@...>]

On 17-Aug-05, at 1:20 PM, Chris Marrin wrote:

> I see it most often for "standard" things like Math. Rather than 
> importing each one separately you can bring in all the functions, like 
> this maybe:
>
>     import("Math","all")
>     local r = min(1,log(sin(PI*2*fraction)))
>
> which looks a lot nicer than:
>
>     require"Math"
>     local r = Math.min(1,Math.log(Math.sin(Math.PI*2*fraction)))

Call me slow, but I just noticed that in lua 5.1work6, you can use:

  str:sub(2, 2)

instead of

  string.sub(str, 2, 2)

Oddly (perhaps), lmathlib does not add itself to the metatable for 
numbers, but there's no obvious reason why it shouldn't, allowing this 
lovely syntax:

> pi = require"math".pi
> fraction = 0.4
> =(1):min( (pi*2*fraction):sin():log() )
-0.53139361498122

OK, it was (mostly) a joke. But for what it's worth, here's the patch 
(code copied from lstrlib.c):

----------------CUT HERE------------------------
--- src/lmathlib.c      Fri Mar  4 13:57:03 2005
+++ src/loomathlib.c    Thu Aug 18 15:36:29 2005
@@ -244,12 +244,23 @@
   {NULL, NULL}
 };

+static void createmetatable (lua_State *L) {
+  lua_newtable(L);
+  lua_pushnumber(L, 0);
+  lua_pushvalue(L, -2);
+  lua_setmetatable(L, -2);
+  lua_pop(L, 1);
+  lua_pushvalue(L, -2);
+  lua_setfield(L, -2, "__index");
+  lua_pop(L, 1);
+}

 /*
 ** Open math library
 */
 LUALIB_API int luaopen_math (lua_State *L) {
   luaL_openlib(L, LUA_MATHLIBNAME, mathlib, 0);
+  createmetatable(L);
   lua_pushnumber(L, PI);
   lua_setfield(L, -2, "pi");
   lua_pushnumber(L, HUGE_VAL);
----------------CUT HERE------------------------

This does have the consequence that:

> =fraction.pi
3.1415926535898