Pythonic Functional Constructs

pyfnz's goal is to offer pythonic implementations of functional programming constructs found in languages such as haskell, scala, and clojure.

Category Theory

• Either: An implementation of scalaz's \/.
• Try: An implementation of scala's Try.

Either

add4 = lambda x: x + 4
div2 = lambda x: Right(x/2) if x != 0 else Left('boom')

# map
>>> Right(2).map(add4)
Right(6)
>>> Left('boom').map(add4)
Left('boom')

# flatmap (bind in haskell)
>>> Right(10).flatmap(div2)
Right(5)
>>> Right(0).flatmap(div2)
Left('boom')
>>> Left('pow').flatmap(div2)
Left('pow')

# do/for notation
>>> Either.do(x * y
              for x in Right(10)
              for y in div2(x))
Right(50)
>>> Either.do(x * y
              for x in Left('pow')
              for y in div2(x))
Left('pow')

Try

add4     = lambda x: x + 4
safe_int = lambda x: Try(int, x)
safe_bin = lambda x: Try(bin, x)

# map
>>> safe_int('5').map(add4)
Success(9)
>>> safe_int('a').map(add4)
Failure(ValueError("invalid literal for int() with base 10: 'a'",))

# flatmap (bind in haskell)
>>> safe_int('5').flatmap(safe_bin)
Success('0b101')
>>> safe_int('a').flatmap(safe_bin)
Failure(ValueError("invalid literal for int() with base 10: 'a'",))

# do/for notation
>>> Try.do(x * y
           for x in safe_int('6')
           for y in safe_int('7'))
Success(42)
>>> Try.do(x * y
           for x in safe_int('a')
           for y in safe_int('7'))
Failure(ValueError("invalid literal for int() with base 10: 'a'",))

Pyjure

Pythonic implementations of core clojure utilities are located in the pyfnz.clj module.

Installing

The pyfnz package is available on PyPi.

pip install pyfnz

$ python
Python 2.7.10 (default, Jul 14 2015, 19:46:27)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.39)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pyfnz
>>> pyfnz.Try(lambda: 1/0)
Failure(ZeroDivisionError('integer division or modulo by zero',))

Testing

All functions have associated tests to both validate functionality and demonstrate example usage and expected output.

python -m unittest discover -s tests