memoizing lambda

def lambda_mem(f, cache=nil)
  cache = {} if cache.nil?
  lambda do |h|
    return cache[h] if cache[h]
    cache[h] = f.call( lambda {|n| lambda_mem(f, cache).call(n) } ).call(h)
  end
end

def fib(g)
  raise(ArgumentError, "Argument must be positive") if g < 0
  lambda_mem(
    lambda {|g| lambda {|n| [0,1][n] ? n : g.call(n - 1) + g.call(n - 2) } }
  ).call(g)
end

puts fib(100)