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Unlifted newtypes via GADTSyntax

    • Closed Issue created by Krzysztof Gogolewski @monoidal

    GHC disallows to define a newtype of an unlifted type (newtype A = A Int#). However, this restriction is not enforced when the newtype is defined using GADT syntax:

    newtype A where
  A :: Int# -> A

    For example, I can derive Show for A and on my machine main = print (A 0#) segfaults.

    Tested on GHC 8.0.1 and master.

    Trac metadata
    Trac field Value
    Version 8.0.1
    Type Bug
    TypeOfFailure OtherFailure
    Priority normal
    Resolution Unresolved
    Component Compiler (Type checker)
    Test case
    Differential revisions
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    Operating system
    Architecture
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