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[Python-ideas] Function composition (was no subject)

David Mertz mertz at gnosis.cx
Sat May 9 20:30:17 CEST 2015 
On Sat, May 9, 2015 at 1:16 PM, Steven D'Aprano <steve at pearwood.info> wrote:

> On Sat, May 09, 2015 at 11:38:38AM -0400, Ron Adam wrote:
>
> > How about an operator for partial?
> >
> >           root @ mean @ map $ square(xs)
>

I have trouble seeing the advantage of a special function composition
operator when it is easy to write a general 'compose()' function that can
produce such things easily enough.

E.g. in a white paper I just did for O'Reilly on _Functional Programming in
Python_ I propose this little example implementation:

def compose(*funcs):
    "Return a new function s.t. compose(f,g,...)(x) == f(g(...(x)))"
    def inner(data, funcs=funcs):
        result = data
        for f in reversed(funcs):
            result = f(result)
        return result
    return inner

Which we might use as:

  RMS = compose(root, mean, square)
  result = RMS(my_array)

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