Re: [proposal] limit(n, ...)

[Daniel Silverstone <dsilvers@...>]

On Thu, Oct 10, 2019 at 08:54:08 -0300, Soni L. wrote:
> it'd be nice to have a limit() function companion to select() where select
> skips the first n and limit skips everything after n.
> 
> e.g. limit(1) --> nothing, limit(1, 1, 2, 3) --> 1, etc

In most languages this would be called "take" and it is indeed a useful
thing to be able to do.

I'd guess an implementation might look like:

```c
static int
lua_take(lua_State *L)
{
    lua_Integer n_items = MIN(luaL_checkinteger(L, 1), lua_gettop(L, -1) - 1);
    lua_remove(L, 1);
    lua_settop(L, n_items);
    return n_items;
}
```

It has been a while since I wrote Lua/C code though, so who knows how badly
wrong that is :D

For your first example, the stack is [1] on input, so n_items is set to MIN(1,
1 - 1) which will be 0.  We remove the 1, set top to 0 and return 0 items,
matching your limit(1) --> nothing.

For your second example, the stack is [1 1 2 3] on input, so n_items is set to
MIN(1, 4 - 1) which will be 1.  Remove the 1, truncate to 1 items, return it.
Works again.

D.

-- 
Daniel Silverstone                         http://www.digital-scurf.org/
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