[Haskell-cafe] Re: haskell programming guidelines

John Meacham john at repetae.net
Wed Feb 22 08:20:03 EST 2006

On Wed, Feb 22, 2006 at 01:14:41PM +0100, Christian Maeder wrote:
> John Meacham wrote:
> >f x = ... y ... where
> >        Just y = Map.lookup x theMap
> >
> >now if the lookup fails you automatically get an error message pointing
> >to the exact line number of the failure. or if the failure message of
> >the routine is more important than the source location you can do
> >
> >f x = ... y ... where
> >        Identity y = Map.lookup x theMap
> These are potential runtime errors, that may be not so obvious to see in
> the source (ie. for user defined types) and even the compiler (ghc) does
> not emit a warning.

Indeed, that is the entire point of the construct. ghc definitly should
not emit a warning in this case as it is what lazy pattern matching
is for.


John Meacham - ⑆repetae.net⑆john⑈

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