#2701: Cannot derive Data for structures containing unboxed values
---------------------------------+------------------------------------------
Reporter: batterseapower | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.10.1 | Severity: normal
Keywords: | Testcase:
Architecture: Unknown/Multiple | Os: Unknown/Multiple
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Trying to compile this:
{{{
{-# LANGUAGE MagicHash, DeriveDataTypeable #-}
module Test where
import GHC.Prim
import Data.Data
import Data.Typeable
data Foo = MkFoo Int#
deriving (Typeable, Data)
}}}
Results in an error:
{{{
$ ghc/stage1-inplace/ghc --make ~/DerivingUnboxed.hs
[1 of 1] Compiling Test (
/Users/mbolingbroke/DerivingUnboxed.hs,
/Users/mbolingbroke/DerivingUnboxed.o )
/Users/mbolingbroke/DerivingUnboxed.hs:10:29:
Couldn't match kind `#' against `*'
When matching the kinds of `Int# :: #' and `d :: *'
Expected type: d
Inferred type: Int#
In the first argument of `z', namely `MkFoo'
/Users/mbolingbroke/DerivingUnboxed.hs:10:29:
Couldn't match kind `#' against `*'
When matching the kinds of `Int# :: #' and `b :: *'
Expected type: b
Inferred type: Int#
In the first argument of `z', namely `MkFoo'
}}}
I'm not sure if this is really a bug or not. It might be nice if deriving
Data handled this case by reboxing Int#, or alternatively if it gave a
clear error messages about not being able to handle unboxed values.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2701>
GHC <http://www.haskell.org/ghc/>
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