|Pathologically Eclectic Rubbish Lister|
Re^2: RFC: A Perlesque Introduction to Haskell, Part One (draft)by FoxtrotUniform (Prior)
|on Jun 23, 2004 at 22:26 UTC||Need Help??|
What you call extensionality is what I've known as currying.
Then I should do a better job.
Extensionality says that the following two definitions are equivalent:
The reason this works is that xs is free on both sides of bar: it's basically a placeholder that says "a list should go here". Both of these functions have type (a -> a) -> [a] -> a (modulo monomorphism-restriction annoyances).
On the other hand, the function application
is a curried expression: while foldl f xs returns a scalar, foldl f returns a function from lists to scalars. To me, currying means partial function application, and it's useful for producing ad-hoc functions where lambda is overkill.
I like your point that currying is easier to understand when you know about type signatures, and thanks for the link to MJD's talk.