What you call extensionality is what I've known
Then I should do a better job.
Extensionality says that the following two
definitions are equivalent:
foo = foldl1 f
bar xs = foldl1 f xs -- note: xs is free on both sides
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
On the other hand, the function application
foldl f -- note: not a definition (type is [a] -> a)
is a curried expression: while foldl f xs
returns a scalar, foldl f
returns a function
from lists to scalars
. To me, currying
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.
Found a typo in this node? /msg me
% man 3 strfry
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