From: timr <timrandg@...>
Date: 2010-11-13T04:15:14+09:00
Subject: Re: Scheme's (cond ((assertion) (value))...(else (value))) statement implemented in ruby?

On Nov 12, 4:42 am, Josh Cheek <josh.ch...@gmail.com> wrote:
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> On Thu, Nov 11, 2010 at 7:20 PM, timr <timra...@gmail.com> wrote:
> > Hi Rubyists,
> > I love ruby, but am learning scheme and kinda like the (cond
> > ((assertion) (value))...(else (value))) syntax for what would normally
> > look like this in ruby:
>
> > if (assertion 1)
> >  value 1
> > elsif (assertion 2)
> >  value 2
> > else
> >  default
> > end
>
> > I find scheme's cond syntax more quickly digestible since it reads
> > like a table.
> > (cond
> >    ((assertion 1) (value 1))
> >    ((assertion 2) (value 2))
> >                (else (default)))
>
> > So I wondered if I could get a similar looking function in ruby. Here
> > is an attempt:
>
> > class Object
> >  alias l lambda
>
> >  def cond(tests)
> >    #acts similar to scheme/LISP cond function using hash
> >    #key => value rather than scheme's (cond (assertion)(value)...
> > (else(value)))
> >    tests.each_pair do |k,v|
> >      if k.call
> >        v.call
> >        break
> >      else
> >        next
> >      end
> >    end
> >  end
>
> >  def end_cond; l{true}; end
> > end
>
> > cond  l{3 < 2}      =>  l{ puts "3 is less than 2"},
> >         l{3 > 3}      =>  l{ puts "3 is greater than 3"},
> >         l{3+1 > 4}  =>  l{ puts "4 is greater than 4"},
> >       end_cond    =>  l{ puts "hey, it works!"}
>
> > # >> hey, it works!
>
> How about chaining ternary operators?
>
> 3   < 2 ? puts("3 is less than 2")      :
> 3   > 3 ? puts("3 is greater than 3")   :
> 3+1 > 4 ? puts("4 is greater than 4")   :
>           puts("hey, it works!")

Woa, that is slick!