On 17 Aug 2009, at 09:43 , Steven D'Aprano wrote:
On Mon, 17 Aug 2009 08:10:16 am Martin v. Löwis wrote:
I don't think he did. Comparing it to the one obvious solution (use
a lambda expression), his only reasoning was "it is much easier to
read". I truly cannot believe that a compose function would be
easier to read to the average Python programmer: if you have
def foo(data):
return compose(a, b(data), c)
what would you expect that to mean?
foo is a factory function that, given an argument `data`, generates a
function b(data), then composes it with two other functions a and c,
and returns the result, also a function.
From his messages, I think Martin's issue with `compose` is with the
composition order rather than the fact that it "pipes" functions:
compose uses the mathematical order, (f ∘ g)(x) = f(g(x)) (so g, the
last function of the composition, is applied first), rather than a
"shell pipe" order of `(f >>> g)(x) = g(f(x))` (where g, the last
function of the composition, is applied last).
For the record, Haskell makes compose a built-in operator:
http://www.haskell.org/haskellwiki/Function_composition
Yes, but Haskell also has a left-to-right composition, the (>>>)
operator: http://haskell.org/ghc/docs/latest/html/libraries/base/Control-Arrow.html#v
:>>>
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