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Simon Peyton Jones authored
As Trac #15436 points out, it is possible to get case dataToTag# (x :: T) of DEFAULT -> blah1 -1# -> blah2 0 -> blah3 The (-1#) alterantive is unreachable, because dataToTag# returns tags in the range [0..n-1] where n is the number of data constructors in type T. This actually made GHC crash; now we simply discard the unreachable alterantive. See Note [Unreachable caseRules alternatives] in PrelRules
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