Dan Doel dan.doel at
Thu Feb 26 09:47:10 EST 2009

On Thursday 26 February 2009 5:36:05 am Christian Maeder wrote:
> Libraries-List,
> browsing through the sources of Data.List I discovered "select", which
> is only used for the implementation of partition and not exported.
> Can someone explain, why the irrefutable pattern "~" is used? Both
> components are used in both branches.

To see the difference, go into ghci, and define select without the irrefutable 
pattern. Then run the following:

  foldr (select even) ([],[]) [1..]

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