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Simon Peyton Jones authored
This patch was triggered by Trac #11601, where I discovered that -XStrict was really not doing the right thing. In particular, f y = let !(Just x) = blah[y] in body[y,x] This was evaluating 'blah' but not pattern matching it against Just until x was demanded. This is wrong. The patch implements a new semantics which ensures that strict patterns (i.e. ones with an explicit bang, or with -XStrict) are evaluated fully when bound. * There are extensive notes in DsUtils: Note [mkSelectorBinds] * To do this I found I need one-tuples; see Note [One-tuples] in TysWiredIn I updated the user manual to give the new semantics
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