Wed May 23 04:48:18 PDT 2007 [EMAIL PROTECTED]
* Improve the interaction of 'seq' and associated data types
Roman produced programs involving associated types that did not optimise well.
His programs were something like this:
data family T a
data instance T Int = MkT Bool Char
bar :: T Int -> Int
bar t = t `seq` loop 0
where
loop = ...
You'd think that the `seq` should unbox 't' outside the loop, since
a (T Int) is just a MkT pair.
The most robust way to make this happen is for the simplifier to understand
a bit about type-family instances. See
Note [Improving seq]
in Simplify.lhs. We use FamInstEnv.topNormaliseType to do the interesting
work.
To make this happen I did a bit of refactoring to the simplifier
monad.
I'd previously done a very similar transformation in LiberateCase, but it
was happening too late. So this patch takes it out of LiberateCase as
well as adding it to Simplify.
M ./compiler/simplCore/LiberateCase.lhs -70 +6
M ./compiler/simplCore/SimplCore.lhs -7 +10
M ./compiler/simplCore/SimplEnv.lhs -12 +5
M ./compiler/simplCore/SimplMonad.lhs -24 +37
M ./compiler/simplCore/Simplify.lhs -30 +86
M ./compiler/types/FamInstEnv.lhs -84 +89
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