Function composition

[piet at cs.uu.nl]

>>>>> cg at gaia.cdg.acriter.nl (Cees de Groot) (CdG) writes:

CdG> I was showing a Math PhD/Functional programming guy Python, and of
CdG> course he was interested in map, filter, etcetera. He talked about
CdG> function composition, and I did a quick:

CdG> def compose(f, g): return lambda x: f(g(x))

This won't work because python doesn't have nested scopes.
The following works, however:

def compose(f, g):
   return lambda x,f=f,g=g: f(g(x))

>>> def compose(f, g):
...    return lambda x,f=f,g=g: f(g(x))
... 
>>> from math import sin,cos
>>> sincos = compose (sin,cos)
>>> sincos(0)
0.841470984808
>>> sin(1)
0.841470984808
- 
Piet van Oostrum <piet at cs.uu.nl>
URL: http://www.cs.uu.nl/~piet [PGP]
Private email: P.van.Oostrum at hccnet.nl