型なしラムダを実装する的なやつの途中まで from 『アンダースタンディング・コンピュテーション』より

l.py

# -*- coding: utf-8 -*-
from __future__ import print_function

# Primitive
ZERO  = lambda f: lambda x: x
ONE   = lambda f: lambda x: f(x)
TWO   = lambda f: lambda x: f(f(x))
THREE = lambda f: lambda x: f(f(f(x)))

# Pair
PAIR  = lambda x: lambda y: lambda f: f(x)(y)
LEFT  = lambda p: p(lambda x: lambda y: x)
RIGHT = lambda p: p(lambda x: lambda y: y)

# Calc
INC   = lambda n: lambda p: lambda x: p(n(p)(x))
SLIDE = lambda p: PAIR(RIGHT(p))(INC(RIGHT(p)))
DEC   = lambda n: LEFT(n(SLIDE)(PAIR(ZERO)(ZERO)))

TRUE  = lambda x: lambda y: x
FALSE = lambda x: lambda y: y

# Syntax
OLD_IF      = lambda f: lambda x: lambda y: f(x)(y)
IF          = lambda f: f
IS_ZERO     = lambda n: n(lambda x: FALSE)(TRUE)

# Lambda -> Any Types
lambda_int  = lambda f: f(lambda x: x + 1)(0)
lambda_bool = lambda f: IF(f)(True)(False)

print(lambda_int(ZERO))
print(lambda_int(TWO))
print(lambda_int(THREE))

print(lambda_bool(TRUE))
print(lambda_bool(FALSE))

print(IF(TRUE)('はい')('いいえ'))
print(IF(FALSE)('はい')('いいえ'))

print(lambda_bool(IS_ZERO(ZERO)))
print(lambda_bool(IS_ZERO(TWO)))

my_pair = PAIR(THREE)(ZERO)
my_pair_two = PAIR(PAIR(ZERO)(TWO))(ONE)

print(lambda_int(LEFT(my_pair)))
print(lambda_int(RIGHT(my_pair)))

print(lambda_int(LEFT(LEFT(my_pair_two))))
print(lambda_int(RIGHT(my_pair_two)))
print(lambda_int(INC(THREE)))
print(lambda_int(DEC(TWO)))
print(lambda_int(DEC(ONE)))
print(lambda_int(DEC(DEC(TWO))))