Re: Another example for syntactically lightweight closures
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- Subject: Re: Another example for syntactically lightweight closures
- From: "steve donovan" <steve.j.donovan@...>
- Date: Thu, 7 Feb 2008 11:11:49 +0200
On Feb 7, 2008 4:30 AM, David Manura <dm.lua@math2.org> wrote:
> Approaches for syntactically lightweight closures are also discussed in [1].
>
> [1] http://lua-users.org/wiki/ShortAnonymousFunctions
>
I particularly liked the trick where one makes code strings executable
functions. This combines a few ideas in the discussion, and implements
a simple form of caching.
local llookup = {}
getmetatable('').__call = function(s,...)
local args,body = s:match('%s*|(.-)|%s*(.+)')
if not args then
args = ''
body = s
end
s = 'function('..args..') return '..body..' end'
local fun = llookup[s]
if not fun then
print 'compiling'
local code = "return " .. s
fun = assert(loadstring(code))()
llookup[s] = fun
end
return fun(...)
end
print(("|x,y| x+y")(2,3))
print( ("|x,y| x+y")(20,30))
function for_n(n,fun,...)
for i = 1,n do fun(...) end
end
for_n(3,"print(42)")
output:
compiling
5
50
compiling
42
42
42
steve d.