Rubyでリスト内包表記

gistfile1.rb

require 'continuation'

def shift
  callcc {|c1| $ctn.(yield(proc {|v| callcc {|c2| $ctn = c2; c1.(v) } })) }
end

def reset
  callcc {|c| $ctn = c; v = yield; $ctn.(v) }
end

def cmpr
  reset { [ yield ] }
end

def range(xs)
  shift {|k| xs.map{|x| k[x]}.flatten(1) }
end

def guard(cond)
  range([]) unless cond
end

#使用例
cmpr {
  x = range(1 .. 3)
  y = range(1 .. 6)
  guard( x + y == 3 )
  [x, y]
}