[Haskell-cafe] Haskell Quick Reference (1-page PDF)

[Joachim Breitner]

Hi,

the reference suggests the use of otherwise (instead of _) as the
default pattern in a case expression. While it certainly works, isn’t it
bad style, as it shadows Prelude.otherwise:

$ cat otherwise.lhs ; runhaskell otherwise.lhs 
>demo b arg = case b of
>               True      -> do print "First arg was True"
>                               let g | arg ==  "Something" = print "Got something"
>                                     | otherwise           = print "Got anything else"
>                               g
>               otherwise -> do print "First arg was not True"
>                               let g | arg ==  "Something" = print "Got something"
>                                     | otherwise           = print "Got anything else"
>                               g
>
>main = do demo True "Something"
>          demo True "Something else"
>          demo False "Something"
>          demo False "Something else"
"First arg was True"
"Got something"
"First arg was True"
"Got anything else"
"First arg was not True"
"Got something"
"First arg was not True"
otherwise.lhs: otherwise.lhs:(7,36)-(8,86): Non-exhaustive patterns in function g

I know that this is a contrieved example (using case on a boolean), but
in other cases you’ll get strange type errors. So while I think I did it
in the past, otherwise should be avoided in case expressions. 

Greetings,
Joachim

-- 
Joachim "nomeata" Breitner
  mail: mail at joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C
  JID: nomeata at joachim-breitner.de | http://www.joachim-breitner.de/
  Debian Developer: nomeata at debian.org
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