Re: Another example for syntactically lightweight closures

["steve donovan" <steve.j.donovan@...>]

On Feb 7, 2008 11:11 AM, steve donovan <steve.j.donovan@gmail.com> wrote:
> print(("|x,y| x+y")(2,3))
>
> print( ("|x,y| x+y")(20,30))

The implementation I presented was of course not optimal, as I
realized about 500ms after hitting send; the lookup was not in the
right place.

local llookup = {}

getmetatable('').__call = function(s,...)
    local fun = llookup[s]
    if not fun then
        local args,body = s:match('%s*|(.-)|%s*(.+)')
        if not args then
            args = ''
            body = s
        end
        local code = 'function('..args..') return '..body..' end'
        print 'compiling'
        code = "return " .. code
        fun = assert(loadstring(code))()
        llookup[s] = fun
    end
    return fun(...)
end

Looking at some timings, comparing '|x| <expr>' with function(x)
return <expr> end;

N = 1,000,0000

x

tring: took    3.23 sec
fun: took    1.13 sec

x*x

string: took    3.34 sec
fun: took    1.28 sec

sin(x)

string: took    7.92 sec
fun: took    5.52 sec

Basically we are paying for the extra function call (__call), but as
the payload takes more time, the difference narrows a lot.

steve d.