From: avi@...4.com (Avi Bryant)
Date: 2002-06-13T10:43:31+09:00
Subject: Re: a new block parameter/variable notation (Re: ruby-dev summary 17252-17356)

matz@ruby-lang.org (Yukihiro Matsumoto) wrote in message news:<1023845919.929356.32025.nullmailer@picachu.netlab.jp>...

>  (c-1) local variables assigned by ":=" are in-block variables,
>        otherwise they are method local variables.  If you assigns to
>        an existing local variable, the variable is shadowed, and you
>        will probably be warned.

Matz, what about making this distinction more general than just
block-local vs. method local?  That is, always be able to use := to
create a new binding rather than modifying an existing one.  So, if
you had

def foo
  x := 1
  y := 2
  myproc = lambda{p x, y}
  x := 10
  y = 20
  myproc.call
end

#=> 1
#=> 20

Bindings would be scoped to thier closest enclosing method or block;
using = when no binding already existed for the variable would be the
same as using :=.

My main motivation for wanting this is to ease state management when
using continuations for backtracking - creating new bindings is
obviously safer here than mutating existing ones.

Too lispy?

Alternatively, I wouldn't mind seeing an ML-style

let x = 1 in
  ...
end

But the := thing is probably more Ruby like.

Avi