#4028: Derived Data instance requires Data instances for unused type parameters
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Reporter: igloo | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 6.14.1
Component: Compiler (Type checker) | Version: 6.12.2
Keywords: | Difficulty:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
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First reported here: http://www.haskell.org/pipermail/glasgow-haskell-
users/2010-April/018785.html
With this module:
{{{
{-# LANGUAGE DeriveDataTypeable #-}
import Data.Data
import Data.Typeable
newtype FSVec s a = FSVec {unFSVec :: [a]}
deriving (Eq, Typeable, Data)
}}}
6.12 now has a `Data s` requirement on the `Data (FSVec s a)` instance.
With 6.10.4:
{{{
*Main> :i FSVec
newtype FSVec s a = FSVec {unFSVec :: [a]}
-- Defined at q.hs:7:8-12
instance (Eq a) => Eq (FSVec s a) -- Defined at q.hs:8:14-15
instance (Data a, Typeable s) => Data (FSVec s a)
-- Defined at q.hs:8:28-31
instance Typeable2 FSVec -- Defined at q.hs:8:18-25
}}}
With 6.12 (and the HEAD):
{{{
*Main> :i FSVec
newtype FSVec s a = FSVec {unFSVec :: [a]}
-- Defined at q.hs:7:8-12
instance (Eq a) => Eq (FSVec s a) -- Defined at q.hs:8:14-15
instance (Data s, Data a) => Data (FSVec s a)
-- Defined at q.hs:8:28-31
instance Typeable2 FSVec -- Defined at q.hs:8:18-25
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4028>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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