#2431: allow empty case analysis
---------------------------------+------------------------------------------
Reporter: RalfHinze | Owner:
Type: feature request | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.8.3
Severity: minor | Resolution:
Keywords: empty case analysis | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Changes (by simonpj):
* difficulty: => Unknown
Old description:
> Using -XEmptyDataDecls I can declare an (almost) empty data type.
> data Void
> However, I can't use an empty case to discriminate values of the
> empty type.
>
> This does not work:
> get :: Void -> a
> Only the type signature, but no body. [This would be useful also
> in other circumstances.]
> get :: Void -> a
> get v = case v of { }
> An empty case in the body.
New description:
Using -XEmptyDataDecls I can declare an (almost) empty data type.
{{{
data Void
}}}
However, I can't use an empty case to discriminate values of the
empty type.
This does not work:
{{{
get :: Void -> a
}}}
Only the type signature, but no body. [This would be useful also
in other circumstances.]
{{{
get :: Void -> a
get v = case v of { }
}}}
An empty case in the body.
Comment:
Why is this useful? The only value of type `Void` is bottom.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2431#comment:1>
GHC <http://www.haskell.org/ghc/>
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