Super-monster patch implementing the new typechecker -- at last

[ghc-hetmet.git] / compiler / types / TypeRep.lhs

diff --git a/compiler/types/TypeRep.lhs b/compiler/types/TypeRep.lhs
index 1660267..fafbaab 100644 (file)
--- a/compiler/types/TypeRep.lhs
+++ b/compiler/types/TypeRep.lhs
@@ -7,6 +7,7 @@
 \begin{code}
 -- We expose the relevant stuff from this module via the Type module
 {-# OPTIONS_HADDOCK hide #-}
+{-# LANGUAGE DeriveDataTypeable #-}
 
 module TypeRep (
        TyThing(..), 
@@ -61,6 +62,9 @@ import Class
 import PrelNames
 import Outputable
 import FastString
+
+-- libraries
+import Data.Data hiding ( TyCon )
 \end{code}
 
        ----------------------
@@ -155,6 +159,7 @@ data Type
                        -- of a 'FunTy' (unlike the 'PredType' constructors 'ClassP' or 'IParam')
                        
                        -- See Note [PredTy], and Note [Equality predicates]
+  deriving (Data, Typeable)
 
 -- | The key type representing kinds in the compiler.
 -- Invariant: a kind is always in one of these forms:
@@ -196,6 +201,7 @@ data PredType
   = ClassP Class [Type]                -- ^ Class predicate e.g. @Eq a@
   | IParam (IPName Name) Type  -- ^ Implicit parameter e.g. @?x :: Int@
   | EqPred Type Type           -- ^ Equality predicate e.g @ty1 ~ ty2@
+  deriving (Data, Typeable)
 
 -- | A collection of 'PredType's
 type ThetaType = [PredType]
@@ -443,12 +449,23 @@ pprClassPred :: Class -> [Type] -> SDoc
 pprClassPred clas tys = ppr_type_app TopPrec (getName clas) tys
 
 pprTheta :: ThetaType -> SDoc
-pprTheta theta = parens (sep (punctuate comma (map pprPred theta)))
+-- pprTheta [pred] = pprPred pred       -- I'm in two minds about this
+pprTheta theta  = parens (sep (punctuate comma (map pprPred theta)))
 
 pprThetaArrow :: ThetaType -> SDoc
-pprThetaArrow theta 
-  | null theta = empty
-  | otherwise  = parens (sep (punctuate comma (map pprPred theta))) <+> ptext (sLit "=>")
+pprThetaArrow []     = empty
+pprThetaArrow [pred] 
+  | noParenPred pred = pprPred pred <+> darrow
+pprThetaArrow preds  = parens (sep (punctuate comma (map pprPred preds))) <+> darrow
+
+noParenPred :: PredType -> Bool
+-- A predicate that can appear without parens before a "=>"
+--       C a => a -> a
+--       a~b => a -> b
+-- But   (?x::Int) => Int -> Int
+noParenPred (ClassP {}) = True
+noParenPred (EqPred {}) = True
+noParenPred (IParam {}) = False
 
 ------------------
 instance Outputable Type where