Implement map in ruby using a recursive function that takes a block

map.rb

#!/usr/bin/env ruby -w

def map(l,&f) 
  return [] if l.empty?
  return [ f.call(l.first) ].concat map(l.slice(1..l.length), &f)
end

puts map [1,2,3,4] {|x| x+1}
puts map ['a','b','c','d'] {|x| "#{x} is a letter"}