-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 El sáb, 03-07-2010 a las 15:19 -0700, prad escribió:
:t uncurry u uncurry u :: (Num (b -> c)) => ((b -> c, b -> c), b) -> c we're trying to uncurry something that is already uncurried
and
:t curry c curry c :: (Num (a, b)) => a -> b -> (a, b) -> (a, b) we're trying to curry something that is already curried
3.1 just what are these strange looking things and how should their types be interpreted?
(uncurry u): "given a function from b to c which is an instance of Num, transform the pair of pairs ( (b -> c) , (b -> c) , b) to c. This is easier to see if you replace (b -> c) with a temporary name `f': ((f, f), b) -> c. Remember that GHC doesn't know what "Num" means, so it is free to invent apparently nonsensical typeclass members. (That said, they might actually be meaningful in some contexts; look up Church numerals.) (curry c): you can see this one by re-parenthesizing. (a -> b) -> ((a,b) - -> (a,b)), given that (a,b) is an instance of Num. (Raise a function from a to b, to a function from a pair (a,b) to another pair (a,b).) This too looks odd; but consider Gaussian integers, which are slightly less general, being ((Num a) => (a,a)). You could also think of it as a Num with a "tag" of arbitrary type, ((Num a) => (a,b)). - -- brandon s. allbery [linux,solaris,freebsd,perl] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkwvycwACgkQIn7hlCsL25W7jgCeLdu+iCANQneCHAmGOk4+7QHN 2UAAoJXHCBWP4WaAj9K3Io+pv0h8L1GR =ti56 -----END PGP SIGNATURE-----