Hilco, On 22/06/2012, at 2:54 PM, Hilco Wijbenga wrote:
I'm going through the excellent http://learnyouahaskell.com tutorial. So far it's been pretty easy to follow but now I ran into something that (when I later started reading about maps) do not seem to fully grasp.
I think I'm close to understanding why (++ "!") "bla" returns "bla! instead of "!bla" but I seem to be missing the last step. :-) I noticed that ((++) "!") "bla" does indeed return "!bla". So it seems to be related to the infix property of ++? The types of (++) "!", ((++) "!"), and (++ "!") are all the same so that doesn't tell me much.
This stuff is in a beginner's tutorial? (!?) This is purely a syntactic issue. These things are called "sections". It might be more obvious if we put in some lambda abstractions, which I hope your tutorial has already introduced: (++ "!") = (\x. x ++ "!") ("!" ++) = (\y. "!" ++ y) Yes, it is related to the infix property of ++. You can get similar things going with arbitrary binary (two argument) functions like so: app = (++) -- or whatever (`app` "!") = (\x. x `app` "!") = (\x. app x "!") (and the other way around) cheers peter -- http://peteg.org/