Package: ghc6
Version: 6.8.2-6
Severity: wishlist
If I try to compile or load this program, ghc complains that I need
to pass -XDeriveDataTypeable to enable the derivation of Typeable
instances:
------ begin Test.hs --------
module Test where
import Data.Typeable
data List a = List [a] deriving(Typeable)
-----------------------------
Test.hs:5:0:
Can't make a derived instance of `Typeable (List a)'
(You need -XDeriveDataTypeable to derive an instance for this class)
In the data type declaration for `List'
If I use "newtype" and I have GeneralizedNewtypeDeriving turned on,
however, I get this error:
/tmp/Test.hs:5:0:
Can't make a derived instance of `Typeable (List a)'
(even with cunning newtype deriving:)
In the newtype declaration for `List'
It would be nice if ghc suggested DeriveDataTypeable here too. JFTR,
it does suggest this if newtype deriving is off:
/tmp/Test.hs:5:0:
Can't make a derived instance of `Typeable (List a)'
(You need -XDeriveDataTypeable to derive an instance for this class
Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension)
In the newtype declaration for `List'
Daniel
-- System Information:
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Architecture: i386 (i686)
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Versions of packages ghc6 depends on:
ii gcc 4:4.3.2-1 The GNU C compiler
ii haskell-utils 1.11 Utilities used by the Debian Haske
ii libc6 2.7-13 GNU C Library: Shared libraries
ii libgmp3-dev 2:4.2.2+dfsg-3 Multiprecision arithmetic library
ii libgmp3c2 2:4.2.2+dfsg-3 Multiprecision arithmetic library
ii libncurses5 5.6+20080907-1 shared libraries for terminal hand
ii libreadline5 5.2-3 GNU readline and history libraries
ii libreadline5-dev 5.2-3 GNU readline and history libraries
ii perl [perl5] 5.10.0-14 Larry Wall's Practical Extraction
ghc6 recommends no packages.
Versions of packages ghc6 suggests:
ii ghc6-doc 6.8.2-6 Documentation for the Glasgow Hask
pn ghc6-prof <none> (no description available)
pn haskell-doc <none> (no description available)
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