Re: lists with nil play nice for Lua 5.2
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- Subject: Re: lists with nil play nice for Lua 5.2
- From: David Manura <dm.lua@...>
- Date: Fri, 3 Aug 2007 03:42:15 +0000 (UTC)
Roberto Ierusalimschy <roberto <at> inf.puc-rio.br> writes:
> Another option is to implement tuples. We can implement them as C
> functions with upvalues (PiL2, p. 257).
This was a rather clean approach in pure Lua:
http://lua-users.org/wiki/FunctionalTuples . It has been appended with an
example that handles arbitrary tuple size via code generation. The code
generation is the awkward part and often resembles something like this:
local function make_constructor(n)
local ts = {}; for i=1,n do ts[i] = "a" .. i end
local names = table.concat(ts, ",")
local s = "local " .. names ..
" = ...; return function(f) f(" .. names .. ") end"
return assert(loadstring(s))
end
function tuple(...)
local n = select('#', ...)
return make_constructor(n)(...)
end
The above could be avoided if we could write this (why can't we?):
function tuple(...)
return function(f) return f(...) end
end
It's my opinion that the implementation of varargs in 5.1 is overly restrictive:
http://lua-users.org/wiki/VarargTheSecondClassCitizen
Also noteworthy: not only can tuples be implemented in terms of
functions, but so can Lua tables ( http://lua-users.org/wiki/MutableFunctions )
and probably near any other data structure. That's not to say they necessarily
should be though.