[Haskell-cafe] Problem about pattern matching.

[Magicloud Magiclouds]

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
<schlepptop at henning-thielemann.de> wrote:
> minh thu schrieb:
>> 2010/4/28 Magicloud Magiclouds <magicloud.magiclouds at gmail.com>:
>>> 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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