case with predicates

gistfile1.rb

require 'rubygems'
require 'backports'  # aliases Proc#=== to Proc#call

rs = (0..10000).to_a.sample(30)

rs.each do |r|
  case r
  when lambda { |n| n.zero?       } then puts "#{r} is zero"
  when lambda { |n| (n % 5).zero? } then puts "#{r} is fiven"
  when lambda { |n| (n % 4).zero? } then puts "#{r} is fourven"
  when lambda { |n| (n % 3).zero? } then puts "#{r} is threeven"
  when lambda { |n| n.even?       } then puts "#{r} is even"
  when lambda { |n| n.odd?        } then puts "#{r} is odd"
  else
    raise 'unpossible'
  end
end

@dkubb—

I agree that this opens terrific options for new types of idiomatic Ruby. I would love to see more examples of how people are using this for great justice, but I suspect such examples will be ill-suited to explication in gist form, by virtue of the substance of my complaint.

To be clear, my point is that this specific example should not be emulated. If the predicates are statically defined in the same scope as a case statement, do the simple thing: use the case statement as Matz intended :P

...pardon me while I continue turning into a cantankerous old grump...

I'd still very much like to have &:method work in when arg lists. I spent some time trying to hack parse.y over the weekend, actually, to see if I could make it work in some frankenstein-like manner, but my version of bison seemed not to be playing nicely. :(