Re: [Haskell-cafe] Problem about pattern matching.

Sorry folks, I did not make it clear. The firstDayOfMonth and lastDayOfMonth was defined earlier in let ... in structure. The problem here is, ghc warned me that "_" and "lastDayOfMonth" was overlapped. And the results showed that, everything that should be worked with "Mider" was done by "not_ ...". On Thu, Apr 29, 2010 at 1:51 AM, Henning Thielemann wrote:

minh thu schrieb:

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2010/4/28 Magicloud Magiclouds :

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Hi, I have code as below. How come "case" version works wrong and gives me "overlap" compiling warning? Thanks.  if dayOfMonth == firstDayOfMonth    then v day (x, y)S    else if dayOfMonth == lastDayOfMonth      then not_ $ v day (x, y)      else Mider day (x, y)

 case dayOfMonth of    firstDayOfMonth -> v day (x, y)    lastDay -> not_ $ v day (x, y)    _ -> Mider day (x, y)

Hi,

firstDayIfMonth and lastDay are new variables, not previously bound variable. This means that trying to pattern match (the value of) dayOfMonth will always succeed with the first alternative.

You can however simulate a 'case' with predefined variables:   http://haskell.org/haskellwiki/Case

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