#4116: Type supplement for constructor specific uses of sum types
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Reporter: gabrielrf | Owner:
Type: proposal | Status: new
Priority: normal | Component: Compiler
Version: 6.13 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by gabrielrf):
Further extension:
since we try to propagate case analysis
we can express the type supplement as a set of disjoint patterns, as masks
for the different branches
{{{
hd :: (List2 a) @ { Cons a _ | Cons2 a _ _ } -> a
hd (Cons x _) = x
hd (Cons2 x _ _) = x
}}}
as reflected by Wren NG Thornton in
http://article.gmane.org/gmane.comp.lang.haskell.cafe/75669
making possible nested patterns
{{{
headFromJust :: (Maybe a) @ {Just a:_} -> a
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4116#comment:4>
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