Complete the evidence generation for GADTs

[ghc-hetmet.git] / compiler / hsSyn / HsBinds.lhs

diff --git a/compiler/hsSyn/HsBinds.lhs b/compiler/hsSyn/HsBinds.lhs
index 31c1cae..900b800 100644 (file)
--- a/compiler/hsSyn/HsBinds.lhs
+++ b/compiler/hsSyn/HsBinds.lhs
@@ -16,14 +16,16 @@ import {-# SOURCE #-} HsExpr ( HsExpr, pprExpr, LHsExpr,
 import {-# SOURCE #-} HsPat  ( LPat )
 
 import HsTypes         ( LHsType, PostTcType )
-import Type            ( Type )
+import PprCore         ( {- instances -} )
+import Coercion                ( Coercion )
+import Type            ( Type, pprParendType )
 import Name            ( Name )
 import NameSet         ( NameSet, elemNameSet )
 import BasicTypes      ( IPName, RecFlag(..), InlineSpec(..), Fixity )
 import Outputable      
 import SrcLoc          ( Located(..), SrcSpan, unLoc )
 import Util            ( sortLe )
-import Var             ( TyVar, DictId, Id )
+import Var             ( TyVar, DictId, Id, Var )
 import Bag             ( Bag, emptyBag, isEmptyBag, bagToList, unionBags, unionManyBags )
 \end{code}
 
@@ -296,20 +298,59 @@ instance (OutputableBndr id) => Outputable (IPBind id) where
 %************************************************************************
 
 \begin{code}
--- A Coercion is an expression with a hole in it
+-- A ExprCoFn is an expression with a hole in it
 -- We need coercions to have concrete form so that we can zonk them
 
 data ExprCoFn
   = CoHole                     -- The identity coercion
-  | CoCompose ExprCoFn ExprCoFn
-  | CoApps ExprCoFn [Id]               -- Non-empty list
-  | CoTyApps ExprCoFn [Type]           --   in all of these
-  | CoLams [Id] ExprCoFn               --   so that the identity coercion
-  | CoTyLams [TyVar] ExprCoFn          --   is just Hole
-  | CoLet (LHsBinds Id) ExprCoFn       -- Would be nicer to be core bindings
+
+  | CoCompose ExprCoFn ExprCoFn        -- (\a1..an. []) `CoCompose` (\x1..xn. [])
+                               --      = (\a1..an \x1..xn. [])
+
+  | ExprCoFn Coercion          -- A cast:  [] `cast` co
+                               -- Guaranteedn not the identity coercion
+
+  | CoApp Var                  -- [] x; the xi are dicts or coercions
+  | CoTyApp Type               -- [] t
+  | CoLam Id                   -- \x. []; the xi are dicts or coercions
+  | CoTyLam TyVar              -- \a. []
+
+       -- Non-empty bindings, so that the identity coercion
+       -- is always exactly CoHole
+  | CoLet (LHsBinds Id)                -- let binds in []
+                               -- (ould be nicer to be core bindings)
+
+instance Outputable ExprCoFn where 
+  ppr co_fn = pprCoFn (ptext SLIT("<>")) co_fn
+
+pprCoFn it CoHole = it
+pprCoFn it (CoCompose f1 f2) = pprCoFn (pprCoFn it f2) f1
+pprCoFn it (ExprCoFn co)     = it <+> ptext SLIT("`cast`") <+> pprParendType co
+pprCoFn it (CoApp id)    = it <+> ppr id
+pprCoFn it (CoTyApp ty)  = it <+> ptext SLIT("@") <+> pprParendType ty
+pprCoFn it (CoLam id)    = ptext SLIT("\\") <> pprBndr LambdaBind id <> dot <+> it
+pprCoFn it (CoTyLam tv)  = ptext SLIT("/\\") <> pprBndr LambdaBind tv <> dot <+> it
+pprCoFn it (CoLet binds) = sep [ptext SLIT("let") <+> braces (ppr binds), it]
 
 (<.>) :: ExprCoFn -> ExprCoFn -> ExprCoFn
-(<.>) = CoCompose
+CoHole <.> c = c
+c <.> CoHole = c
+c1 <.> c2    = c1 `CoCompose` c2
+
+mkCoTyApps :: [Type] -> ExprCoFn
+mkCoTyApps tys = mk_co_fn CoTyApp (reverse tys)
+
+mkCoApps :: [Id] -> ExprCoFn
+mkCoApps ids = mk_co_fn CoApp (reverse ids)
+
+mkCoTyLams :: [TyVar] -> ExprCoFn
+mkCoTyLams ids = mk_co_fn CoTyLam ids
+
+mkCoLams :: [Id] -> ExprCoFn
+mkCoLams ids = mk_co_fn CoLam ids
+
+mk_co_fn :: (a -> ExprCoFn) -> [a] -> ExprCoFn
+mk_co_fn f as = foldr (CoCompose . f) CoHole as
 
 idCoercion :: ExprCoFn
 idCoercion = CoHole