Channel 9 Forums - Tech Off - Haskell question http://mschnlnine.vo.llnwd.net/d1/Dev/App_Themes/C9/images/feedimage.png Channel 9 Forums - Tech Off - Haskell question http://channel9.msdn.com/Forums Channel 9 keeps you up to date with the latest news and behind the scenes info from Microsoft that developers love to keep up with. From LINQ to SilverLight – Watch videos and hear about all the cool technologies coming and the people behind them. http://channel9.msdn.com/Forums en Fri, 24 May 2013 00:44:03 GMT Fri, 24 May 2013 00:44:03 GMT Rev9 3 -3 -1 Tech Off - Haskell question Can somebody explain to me why the following works:


add2 = foldr (\ x xs -> x + 2 : xs) []

 

but this does not:

appendTest = foldr(\ x xs -> x ++ "Test" : xs) []

 

I get a type mismatch between [[[Char]]] and [[Char]] when I call

appendTest ["one", "two"]

 

I need to do it this way:

 

appendTest = foldr(\ x xs -> (\ x -> x++ "Test") : xs) []

 

I am not sure why though, especially since the Int example works. Sure, String is [Char], but I can't see why the first version of appendTest expects a [[[Char]]] instead of a [[Char]].

 

Thanks a lot!

]]> http://channel9.msdn.com/Forums/TechOff/519580-Haskell-question/519580#519580 Sun, 10 Jan 2010 10:11:18 GMT http://channel9.msdn.com/Forums/TechOff/519580-Haskell-question/519580#519580 trifonius 3 http://channel9.msdn.com/Niners/trifonius/Discussions/RSS Tech Off - Haskell question Have you tried reformulating as separate functions rather than "trying to be smart on the first go" with the embedded lambda expression? When I'm doing Haskell it helps to identify problem areas.

]]> http://channel9.msdn.com/Forums/TechOff/519580-Haskell-question/22b8fa17d0a84538aa439deb000b5faf#22b8fa17d0a84538aa439deb000b5faf Sun, 10 Jan 2010 12:32:18 GMT http://channel9.msdn.com/Forums/TechOff/519580-Haskell-question/22b8fa17d0a84538aa439deb000b5faf#22b8fa17d0a84538aa439deb000b5faf W3bbo 3 http://channel9.msdn.com/Niners/W3bbo/Discussions/RSS Tech Off - Haskell question it may be due to + binding with higher precedence compared to : in comparison with ++

placing brackets like should work (x ++ "Test")

]]> http://channel9.msdn.com/Forums/TechOff/519580-Haskell-question/a6fd8659a43c406380af9deb000b5ff7#a6fd8659a43c406380af9deb000b5ff7 Tue, 02 Feb 2010 15:57:02 GMT http://channel9.msdn.com/Forums/TechOff/519580-Haskell-question/a6fd8659a43c406380af9deb000b5ff7#a6fd8659a43c406380af9deb000b5ff7 Amar Nath Satrawala 3 http://channel9.msdn.com/Niners/A N Satrawala/Discussions/RSS