60 lines
1.3 KiB
Python
60 lines
1.3 KiB
Python
'''First-class functions'''
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from math import (acos, cos, asin, sin)
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from inspect import signature
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# main :: IO ()
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def main():
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'''Composition of several functions.'''
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pwr = flip(curry(pow))
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fs = [sin, cos, pwr(3.0)]
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ifs = [asin, acos, pwr(1 / 3.0)]
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print([
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f(0.5) for f in
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zipWith(compose)(fs)(ifs)
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])
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# GENERIC FUNCTIONS ------------------------------
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# compose (<<<) :: (b -> c) -> (a -> b) -> a -> c
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def compose(g):
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'''Right to left function composition.'''
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return lambda f: lambda x: g(f(x))
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# curry :: ((a, b) -> c) -> a -> b -> c
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def curry(f):
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'''A curried function derived
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from an uncurried function.'''
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return lambda a: lambda b: f(a, b)
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# flip :: (a -> b -> c) -> b -> a -> c
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def flip(f):
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'''The (curried or uncurried) function f with its
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two arguments reversed.'''
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if 1 < len(signature(f).parameters):
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return lambda a, b: f(b, a)
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else:
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return lambda a: lambda b: f(b)(a)
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# zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
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def zipWith(f):
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'''A list constructed by zipping with a
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custom function, rather than with the
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default tuple constructor.'''
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return lambda xs: lambda ys: [
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f(a)(b) for (a, b) in zip(xs, ys)
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]
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if __name__ == '__main__':
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main()
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