From: ichimal@...
Date: 2003-02-03T20:33:18+09:00
Subject: Re: Local variables & blocks

Hi folks. How do you do?

In message "Re: Local variables & blocks"
    on 03/02/03, mats writes:

>|I just wonder what the second invocation of blocktest() will print. Since
>|there is no iteration, no assignment to 'foo' will have taken place. Is
>|this an error or will 'foo' be initialized with 'nil'?  I guess 'nil'
>|initialization will be more reasonable because it saves an additional test.
>
>nil.  Right again. ;-)

  I think, it should be a first-class special value like #<non-initialized>.

  For example:

    def blocktest(args)
      args.each do |arg|
        foo = foo and arg
      end
      foo
    end

    arg1 = []
    arg2 = [nil, nil, nil]

    result1 = blocktest(arg1)
    result2 = blocktest(arg2)

    ...

case 1: blocktest returns a nil as the non-initialized value:
    if result1 then
        do_something
    elsif arg1.length > 0 then     # Is arg1 really [] yet?
        do_something
    else
        do_something
    end

case 2: blocktest returns a #<non-initialized>
    case result1
    when nil
        do_something
    when #<non-initialized>
        do_something
    else
        do_something
    end



  The value nil already have a special mean. Double meaning may be more
harmful idea than shadowing, I think.

c.f. #f, nil and () in Lisp/Scheme.

I'm sorry my poor English.
Thanks.

----
1002.(ichimal@fenix.ne.jp)
SUZUKI Shingo