Ruby != Lisp

gistfile1.rb

def cons(x, xs)
  lambda { |f| f.call(x, xs) }
end

def car(f)
  f.call(lambda { |x, xs| x })
end

def cdr(f)
  f.call(lambda { |x, xs| xs })
end

def fold(xs, seed, f)
  while xs != nil do
    seed = f.call(seed, car(xs))
    xs = cdr(xs)
  end
  seed
end

def rev(xs)
  fold(xs, nil, lambda { |xs, x| cons(x, xs)})
end

def map(xs, f)
  rev(fold(xs, nil, lambda { |xs, x| cons(f.call(x), xs)}))
end

def filter(xs, f)
  rev(fold(xs, nil, lambda { |xs, x| if f.call(x) then cons(x, xs) else xs end }))
end

def iter(xs, f)
  fold(xs, nil, lambda { |_, x| f.call(x) })
end

def append(xs, ys)
  if xs == nil then ys
  elsif ys == nil then xs
  else cons(car(xs), append(cdr(xs), ys))
  end
end

def print_list(xs)
  iter(xs, lambda { |x| puts x })
end

def debug(xs)
  print_list xs
  xs
end

a = debug(cons(1, cons(2, cons(3, nil))))
sum = fold(a, 0, lambda { |a, b| a + b })
b = debug(map(a, lambda { |x| x * 5 }))
c = debug(filter(b, lambda { |x| x <= 10 }))
d = debug(append(append(a, b),c))