Re: function foo() in table
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- Subject: Re: function foo() in table
- From: Sean Conner <sean@...>
- Date: 2014年4月22日 00:14:38 -0400
It was thus said that the Great Dirk Laurie once stated:
> 2014年04月21日 23:33 GMT+02:00 Sean Conner <sean@conman.org>:
> > It was thus said that the Great Coroutines once stated:
> >>
> >> I always remember that local function f() ... end is equivalent to
> >> local f; f = function () ... end because when I have to write
> >> recursive functions it errors when it tries to call the
> >> not-yet-declared identifier from within itself.
>
> s/errors/would otherwise error/
>
> > You should try using the Y combinator.
> >
> > function Y(f)
> > local function g(...) return f(g,...) end
> > return g
> > end
> >
> > print(Y(function(rec, x)
> > if x < 2 then
> > return 1
> > else
> > return x * rec(x-1)
> > end
> > end)(5))
> >
> > -spc (Unfortunately, do declare Y with your conding standard requres the
> > use of Y ... )
>
> I don't understand the very last point made, even after correcting two typos.
You originally stated:
> I have stopped using "local function f()" because I cannot remember
> whether it is the same as "local f = function()" or "local f;
> f=function()". So whichever of those I need, I code explicitly.
Coroutines was stating that
local function f() ... end
is the same as:
local f
f = function() ... end
because otherwise, you couldn't write recursive functions if
local function f() ... end
was equivalent to:
local f = function() ... end
In a way, you could think of
function draw(x1,y1,x2,y3) ... end
as doing
draw = -- some place holding value
draw = function(x1,y1,x2,y2)
which also means that
local function draw(x1,y1,x2,y2) ... end
follows that pattern:
local draw = -- some place holding value
draw = function(x1,y1,x2,y2) ... end
The whole bit I added with the Y combinator was just a riff on the
conversation. You can think of the Y combinator as allowing a anonymous
(non-named) function to call itself (the actual description uses some obtuse
mathematical terms like "fixed point"---I don't pretend to understand what
exactly it means).
-spc (I hope that cleared that up ... )