In defence of the two-namespace rule

[Quinn Dunkan]

On 21 Jan 2000 15:36:53 GMT, Aahz Maruch <aahz at netcom.com> wrote:
>In article <m3n1q0fzg7.fsf at greebo.nodomain.de>,
>Bernhard Herzog  <herzog at online.de> wrote:
>>
>>curried functions
>
>All right, I've seen it enough times this week, would somebody mind
>giving the Stupid Person's definition of currying?

A curried function always takes one argument.  If it needs more values to
'finish', it returns a closure which will accept the next arg.  In python:

>>> def add(a):
...    return lambda b, a=a: a + b
...
>>> add(4)
<function <lambda> at 100b41f8>
>>> add(4)(5)
9

A simple example of how this can be useful:

>>> map(add(5), range(5))
[5, 6, 7, 8, 9]

Many functional languages such as the ml family and haskell have all functions
curried by default, including +, *, etc. (there are no two-argument
functions... of course, you could pass a _single_ tuple of two elements :))

Hugs> map (5+) [0..4]
[5,6,7,8,9]

Whenever you know some args for a function now, and the rest later, you can
partially apply it and toss the closure around.  It's very useful if your
brain is working in the appropriate mode.