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#
# Copyright Applied Language Solutions 2012
#
# This file is part of Pypeline.
#
# Pypeline is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Pypeline is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with Pypeline. If not, see <http://www.gnu.org/licenses/>.
#
import types
from pypeline.core.arrows.arrow import Arrow
#
# An implementation of Arrows with functions. The composition
# operator (>>>) is implemented as the right shift
# operator (>>). Tuple input parallel computation (***) is the
# Python (**) operator. And Parallel computation with a scalar
# input (&&&) is the bitwise and operator (&).
# WATCH OUT FOR OPERATOR PRECEDENCE!!!
#
# ** is higher than >> is higher than than &
#
#
# See:
# Publications:
# http://www.cse.chalmers.se/~rjmh/Papers/arrows.pdf
# http://www.soi.city.ac.uk/~ross/papers/notation.pdf
#
# Tutorials:
# http://www.haskell.org/arrows/
# http://www.haskell.org/haskellwiki/Arrow_tutorial
# http://en.wikibooks.org/wiki/Haskell/Understanding_arrows
#
class FunctionArrow(Arrow):
def __init__(self, func):
if type(func) is not types.FunctionType and \
type(func) is not types.MethodType:
raise ValueError("Must be a function or method")
Arrow.__init__(self)
self._func = func
#
# (>>>) composition
#
# +---------+ +---------+
# b --->+--- f ---+--- c ---->+--- g ---+---> d
# +---------+ +---------+
def __rshift__(self, other):
if not isinstance(other, Arrow):
raise ValueError("Must be an arrow")
return FunctionArrow(lambda b: other._func(self._func(b)))
#
# (***) parallel computation with input of type tuple
#
# +---------+ +---------+
# b --->+--- f ---+---> c --->+---------+---> c
# | | | |
# d --->+---------+---> d --->+--- g ---+---> e
# +---------+ +---------+
def __pow__(self, other):
if not isinstance(other, Arrow):
raise ValueError("Must be an arrow")
return self.first() >> other.second()
#
# (&&&) parallel computation with scalar input
#
# +---------+ +---------+ +---------+
# | /----+---> b --->+--- f ---+---> c --->+---------+---> c
# b --->+---- | | | | |
# | \----+---> b --->+---------+---> b --->+--- g ---+---> d
# +---------+ +---------+ +---------+
def __and__(self, other):
if not isinstance(other, Arrow):
raise ValueError("Must be an arrow")
return split() >> self.first() >> other.second()
#
# First
#
# +---------+
# b --->+--- f ---+---> c
# | |
# d --->+---------+---> d
# +---------+
def first(self):
def composition(a_tuple):
if type(a_tuple) is not types.TupleType:
raise ValueError("Must be a tuple type")
return (self._func(a_tuple[0]), a_tuple[1])
return FunctionArrow(composition)
#
# Second
#
# +---------+
# d --->+---------+---> d
# | |
# b --->+--- f ---+---> c
# +---------+
def second(self):
def composition(a_tuple):
if type(a_tuple) is not types.TupleType:
raise ValueError("Must be a tuple type")
return (a_tuple[0], self._func(a_tuple[1]))
return FunctionArrow(composition)
#
# Apply a value, of appropriate type, to the arrow
#
def __call__(self, value):
return self._func(value)
#
# Split
#
# +-------+
# | /---+---> b
# b --->+--- |
# | \---+---> b
# +-------+
def split():
return FunctionArrow(lambda b: (b, b))
#
# Unsplit
#
# +---------+
# b --->+---\ |
# | (op)---+---> d
# c --->+---/ |
# +---------+
def unsplit(op_func):
return FunctionArrow(lambda t: op_func(t[0], t[1]))
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