Re: callback implementation details..

[Philipp Janda <siffiejoe@...>]

Am 18.10.03 01:01 schröbte Reuben Thomas:
> > Did you try this code? I think it is what you might be looking for,
> > actually. Although you can do it with unpack() etc.
>
>
> Yes, curry is simply:
>
> -- curry: Partially apply a function
> --   f: function to apply partially
> --   a1 ... an: arguments to fix
> -- returns
> --   g: function with ai fixed
> function curry (f, ...)
>   local fix = arg
>   return function (...)
>            return f (unpack (fix), unpack (arg))
>          end
> end

Your version does not work correctly.
If I say

local f = curry( print, 1, 2 )
f( 3, 4 )

I get:
1   3   4
but I should get
1   2   3   4

This is because only the first return value of unpack(fix) is used.
I got that problem with the following helper function:

local function dump( ... )
  io.stdout:write( unpack( arg ), "\n" )
  io.stdout:flush()
end

which only printed the first argument.

For the curry function to work you will need some table merging:

function curry2( f, ... )
  local fix = arg
  return function( ... )
           local params = {}
           for _,a in ipairs( fix ) do
             table.insert( params, a )
           end
           for _,a in ipairs( arg ) do
             table.insert( params, a )
           end
           return f( unpack( params ) )
         end
end

> which is a lot simpler than messing around with C.

Philipp