Hi, Am Samstag, den 28.01.2012, 23:34 -0500 schrieb wren ng thornton:
* Perhaps the most useful is that it packages up Matt Helige's classic multicomposition trick[1]. These combinators allow you to easily modify the types of a many-argument function with syntax that looks like giving type signatures. For example,
foo :: A -> B -> C
albert :: A -> X beth :: B -> Y carol :: C -> Z
bar :: X -> Y -> Z bar = foo $:: albert ~> beth ~> carol
I've found this to be especially helpful for defining non-derivable type class instances for newtypes since it both abstracts away the plumbing and also makes explicit what you mean.
Even without looking at the definition of $:: and ~>, I have doubts about the existence of such a bar function (it calls foo, which needs an A, but it is not given an A and no used function produces one; albert only consumes one). Maybe you mean: foo :: A -> B -> C albert :: X -> A beth :: Y -> B carol :: C -> Z bar :: X -> Y -> Z bar = foo $:: albert ~> beth ~> carol Greetings from POPL, Joachim -- Joachim "nomeata" Breitner mail@joachim-breitner.de | nomeata@debian.org | GPG: 0x4743206C xmpp: nomeata@joachim-breitner.de | http://www.joachim-breitner.de/