compilation of pattern-matching?

Simon Marlow marlowsd at
Fri Mar 27 04:57:50 EDT 2009

Lennart Augustsson wrote:
> Sorting by constructor tag is perfectly safe when done right.
> You can read about how to do it in my 1985 FPCA paper or in Simon's book.
> When pattern matching against against things that that are not
> constructors (like literals etc) it's much trickier to reorder them
> since you have to prove harder pattern commutation properties.
> I don't think there is any controversy at all about Haskell pattern
> matching semantics.
> As you say, it's pretty clearly spelled out.
> (It wouldn't hurt to have it written down as a denotational semantics, though.)
> And ghc happens to have a bug.

Just thought I'd mention this other bug in the same area:
   (Wrong pat-match order for records)


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