[GHC] #8537: confusing error message for specialize pragma

17 Nov 2013

      #8537: confusing error message for specialize pragma
------------------------------------+-------------------------------------
       Reporter:  carter            |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.6.3
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 I get the following confusing error/warning about SPECIALIZE
 {{{

   SPECIALISE pragma for non-overloaded function `$cfmap'

 }}}

 with the following example module

 {{{

 {-# LANGUAGE PolyKinds   #-}
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE NoImplicitPrelude #-}

 module Numerical.Types.Shape where

 import Control.Applicative
 import Data.Foldable
 import Data.Monoid
 import Data.Functor
 import Prelude (seq, ($!),($),Show(..),Eq(),Int)

 data Nat = S !Nat  | Z
     --deriving (Eq,Show,Read)

 {-
 not doing the  HLIST style shape because I don't want to have
 any pattern matchings going on.

 Also would play hell with locality quality in the address translation
 hackery,
 because there'd be an extra load to get those ints!
 -}
 infixr 3 :*

  {-
 the concern basically boils down to "will it specialize / inline well"

  -}
 data Shape (rank :: Nat) a where
     Nil  :: Shape Z a
     (:*) ::  !(a) -> !(Shape r a ) -> Shape  (S r) a

 --deriving instance (Show (Shape rank a))

     -- deriving instance Eq (Shape rank a)

     -- #if defined( __GLASGOW_HASKELL__ ) &&  ( __GLASGOW_HASKELL__  >=
 707)
     --deriving instance Typeable (Shape rank a)
     -- #endif

 instance Functor (Shape Z) where

     fmap  = \ f Nil -> Nil
     {-# INLINABLE fmap #-}

     {-# SPECIALIZE fmap :: (Int ->Int )-> (Shape Z Int)-> (Shape Z Int)
 #-}

 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8537
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