Should exhaustiveness testing be on by default?

Simon Peyton-Jones simonpj at
Tue May 19 03:37:28 EDT 2009

No, the shortcomings are not documented I'm afraid.  It's a squishy question because when you add guards and view patterns it's undecidable whether patterns overlap or are exhaustive.

Still, GHC's current implementation is poor.  It's a well-contained project that is awaiting a competent implementor. see


| -----Original Message-----
| From: glasgow-haskell-users-bounces at [mailto:glasgow-haskell-
| users-bounces at] On Behalf Of Robert Greayer
| Sent: 19 May 2009 04:00
| Cc: glasgow-haskell-users at
| Subject: Re: Should exhaustiveness testing be on by default?
| On Mon, May 18, 2009 at 4:00 PM, Norman Ramsey <nr at> wrote:
| > P.S. The exhaustiveness checker does need improvement...
| Is it documented somewhere what deficiencies the exhaustiveness
| checker has (where it can report problems that don't exist or fails to
| report problems that do...), and which deficiencies can't be resolved?
| Rob
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