Re: Tail Calls for C Functions

[Mark Feldman <mfeldman@...>]

Patrick Donnelly wrote:
> Hi List,
>
> Has there been any thought to adding tail call support to the Lua C
> API? 

+1. Not only does it make it more difficult to replace Lua tail-call 
functions with C code, it also makes it difficult to automatically 
convert the compiled op codes to C for high-performance Lua.

Allowing C functions to be used with coroutines would be nice too. I 
posted code here a few months ago (see below) to show how it can work if 
you remove the function-type check.

Mark Feldman

=== C coroutine ===

#define YIELD() {lua_yield(L, 0); return -1;}

static int foo(lua_State *L)
{
  /* compiler typically implements the case statement with a
     jump table but you could do it manually if you wanted */
  static int foo_state = 0;
  switch (foo_state++)
  {
      case 0:
          lua_getglobal(L, "print");
          lua_pushstring(L, "Hello World!");
          lua_call(L, 1, 0);
          YIELD();  /* fall-throughs allow you to do conditional yields */

      case 1:
          lua_getglobal(L, "print");
          lua_pushstring(L, "Goodbye World!");
          lua_call(L, 1, 0);
  }

  return 1; /* die */
}

=== Lua calling code ===

local co = coroutine.create(foo)
coroutine.resume(co)        --> Hello World!
coroutine.resume(co)        --> Goodbye World!
print(coroutine.status(co))    --> dead


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