Re: Operators on functions

[Pierre-Yves Gérardy <pygy79@...>]

Whoops... a "local " should off course be inserted in the first slot
of the template.
-- Pierre-Yves


On Wed, Nov 20, 2013 at 2:19 AM, Pierre-Yves Gérardy <pygy79@gmail.com> wrote:
> On Tue, Nov 19, 2013 at 7:17 AM, steve donovan
> <steve.j.donovan@gmail.com> wrote:
>> I briefly got very excited about the possibilities of doing this, and
>> in fact seq.import in PL makes all functions accept seq 'methods'.
>> When first experimenting with Microlight I found that composition and
>> binding could be very elegantly expressed in the way you describe
>> (which feels less ad-hoc than the seq hack).  However, it _is_ a
>> global hack.
>
> Slightly OT, but for efficient multi-function composition I use the following:
>
>     cmp_tpl = {1, " = ...; return function(...) return ", 3, "(...", 5, "end"}
>
>     function compose(...)
>         local fns, n = {}, select('#', ...)
>         if n == 0 then return id end
>         for i = 1, n do fns[i] = "f"..i end
>         cmp_tpl[1] = table.concat(fns, ", ")
>         cmp_tpl[3] = table.concat(fns, "(")
>         cmp_tpl[5] = (")"):rep(n)
>         return load(t_concat(cmp_tpl))(...) -- or loadstring
>     end
>     e = compose(f,g,h) --> load("f1, f2, f3 = ...; return
> function(...) return f1(f2(f3(...))) end")(f,g,h)
>
> If you're not scared of metaprogramming, feel free to steal it :-).
>
> -- Pierre-Yves