Skip to content
Snippets Groups Projects

:info pretty-prints data types with non-Type return kinds oddly

    • Closed Issue created by Ryan Scott @RyanGlScott

    Consider this GHCi session:

    $ ghci -XUnboxedTuples
GHCi, version 8.6.3: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/ryanglscott/.ghci
λ> :i (##)
data (##) :: TYPE ('GHC.Types.TupleRep '[]) = (##)
        -- Defined in ‘GHC.Prim’

    Notice that we're printing data (##) :: TYPE ('GHC.Types.TupleRep '[]) = (##). Yuck! Granted, you can't define an unboxed tuple like this anyway, but the presence of that kind signature (which definitely doesn't belong in a Haskell98-style data declaration) makes things worse.

    In case if you're wondering if this is an unboxed tuple–specific problem, it's not. This issue also creeps up in the WIP implementation of unlifted newtypes:

    λ> newtype T = MkT Int#
λ> :i T
newtype T :: TYPE 'IntRep = MkT Int#
        -- Defined at <interactive>:5:1

    However, as this ticket demonstrates, this problem has existed well before the unlifted newtypes patch, and more importantly, this can be fixed independently of that patch.

    Trac metadata
    Trac field Value
    Version 8.6.3
    Type Bug
    TypeOfFailure OtherFailure
    Priority normal
    Resolution Unresolved
    Component Compiler
    Test case
    Differential revisions
    BlockedBy
    Related
    Blocking
    CC
    Operating system
    Architecture
    To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information

    Child items 0

    • No child items are currently assigned. Use child items to break down this issue into smaller parts.

    Activity

    Please register or sign in to reply