lists.hs

let empty selector  = selector True True True
let prepend el list = \selector -> selector el list False
let head list       = list (\h t e -> h)
let tail list       = list (\h t e -> t)
let is_empty list   = list (\h t e -> e)

lists.rb

empty    = ->(selector) { selector[_, _, true] }
prepend  = ->(el, list) { ->(selector) { selector[el, list, false] } }
head     = ->(list) { list[->(h, _, _) { h }] }
tail     = ->(list) { list[->(_, t, _) { t }] }
is_empty = ->(list) { list[->(_, _, e) { e }] }

list = prepend["asdf", empty]
head[list] # => "asdf"

long.rb

empty = lambda do |selector|
  selector.call _, _, true
end

prepend = lambda do |el, list|
  lambda do |selector|
    selector.call el, list, false
  end
end

head = lambda do |list|
  list.call(lambda do |h, _, _|
    h
  end)
end

tail = lambda do |list|
  list.call(lambda do |_, t, _|
    t
  end)
end

is_empty = lambda do |list|
  list.call(lambda do |_, _, e|
    e
  end)
end