From: Josh Cheek <josh.cheek@...>
Date: 2010-11-12T21:42:42+09:00
Subject: Re: Scheme's (cond ((assertion) (value))...(else (value))) statement implemented in ruby?

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On Thu, Nov 11, 2010 at 7:20 PM, timr <timrandg@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!")

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