Python Monad notes

gistfile1.txt

PyMonad
https://pypi.python.org/pypi/PyMonad/
Doesn't duck type Writer - subclass
class StringWriter(Writer):
    logType = str

PyMonads
https://github.com/dustingetz/pymonads
Doesn't duck type Writer:
https://github.com/dustingetz/pymonads/blob/master/writer.py#L6

OSlash
https://pypi.python.org/pypi/OSlash/0.5.1
Same issue with writer https://github.com/dbrattli/OSlash/blob/master/oslash/writer.py#L89

fn
https://pypi.python.org/pypi/fn/0.4.3
No writer at all.
Defines some nice common helper fns rather than needing lots-o-lambdas.

monad
https://bitbucket.org/pyx/monad/
https://pypi.python.org/pypi/monad/0.1
Looks nice and pithy
No writer at all.


Example duck-typing Writer:
from collections import namedtuple

class Writer(namedtuple("Writer", "value log")):

  @classmethod
  def pure(cls, value):
    return Writer(value, None)

  def bind(self, fn):
    newvalue, newlog = fn(self.value)
    if self.log is None:
      resultlog = newlog
    else:
      resultlog = self.log + newlog
    return Writer(newvalue, resultlog)