[Python-Dev] Re: PEP 309, function currying

[Andrew Koenig]

> I like curry(). The others don't bring the right concept to mind for me.
> I apologise if this offends the purists, but *all* of the recent attempts
> to "clarify" the difference between partial application and currying have
> simply confused me.

Let me try an example, partly to be sure I understand it.

Suppose have a function f with five arguments.  Then I think you are
proposing a function, which I shall call X for the moment, with the property
that evaluating

	g = X(f, a, b)
	z = g(c, d, e)

has the same effect as

	z = f(a, b, c, d, e)

At least, that's how the code in the PEP seems to behave.

If so, that's not currying.  Currying would work like this:

	g = curry(f)		# Note -- no other arguments
	g1 = g(a)
	g2 = g1(b)
	g3 = g2(c)
	g4 = g3(d)
	z = g4(e)

with z having the same value as f(a, b, c, d, e) afterward.

Note that curry takes only one argument, namely f.  Instead of taking an
argument of f directly, it returns a function that will accept f's first
argument.  It is that extra level of indirection that distinguishes currying
from partial application.