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Simon Peyton Jones authored
Consider data T a where T1 :: T Int T2 :: T Bool T3 :: T Char f :: T Bool -> Int f x = case x of DEFAULT -> ... T2 -> 3 Here the DEFAULT case covers multiple constructors (T1,T3), but none of them can match a scrutinee of type (T Bool). So we can prune away the default case altogether. In implementing this, I re-factored this bit of the simplifier, elminiating prepareAlts from SimplUtils, and putting all the work into simplAlts in Simplify The proximate cause was a program written by Manuel using PArrays
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