%
+% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[PatSyntax]{Abstract Haskell syntax---patterns}
\begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings
+-- for details
+
module HsPat (
Pat(..), InPat, OutPat, LPat,
- HsConDetails(..), hsConArgs,
+ HsConDetails(..),
+ HsConPatDetails, hsConPatArgs,
+ HsRecFields(..), HsRecField(..), hsRecFields,
mkPrefixConPat, mkCharLitPat, mkNilPat, mkCoPat,
import {-# SOURCE #-} HsExpr ( SyntaxExpr )
-- friends:
-import HsBinds ( DictBinds, HsBind(..), ExprCoFn, isIdCoercion, emptyLHsBinds, pprLHsBinds )
-import HsLit ( HsLit(HsCharPrim), HsOverLit )
-import HsTypes ( LHsType, PostTcType )
-import BasicTypes ( Boxity, tupleParens )
+import HsBinds
+import HsLit
+import HsTypes
+import BasicTypes
-- others:
import PprCore ( {- instance OutputableBndr TyVar -} )
-import TysWiredIn ( nilDataCon, charDataCon, charTy )
-import Var ( TyVar )
-import DataCon ( DataCon, dataConTyCon )
-import TyCon ( isProductTyCon )
+import TysWiredIn
+import Var
+import DataCon
+import TyCon
import Outputable
-import Type ( Type )
-import SrcLoc ( Located(..), unLoc, noLoc )
+import Type
+import SrcLoc
\end{code}
data Pat id
= ------------ Simple patterns ---------------
WildPat PostTcType -- Wild card
+ -- The sole reason for a type on a WildPat is to
+ -- support hsPatType :: Pat Id -> Type
+
| VarPat id -- Variable
| VarPatOut id (DictBinds id) -- Used only for overloaded Ids; the
-- bindings give its overloaded instances
------------ Constructor patterns ---------------
| ConPatIn (Located id)
- (HsConDetails id (LPat id))
+ (HsConPatDetails id)
| ConPatOut {
pat_con :: Located DataCon,
-- including any bound coercion variables
pat_dicts :: [id], -- Ditto dictionaries
pat_binds :: DictBinds id, -- Bindings involving those dictionaries
- pat_args :: HsConDetails id (LPat id),
+ pat_args :: HsConPatDetails id,
pat_ty :: Type -- The type of the pattern
}
| SigPatOut (LPat id) -- Pattern with a type signature
Type
- ------------ Dictionary patterns (translation only) ---------------
- | DictPat -- Used when destructing Dictionaries with an explicit case
- [id] -- superclass dicts
- [id] -- methods
-
------------ Pattern coercions (translation only) ---------------
- | CoPat ExprCoFn -- If co::t1 -> t2, p::t2,
+ | CoPat HsWrapper -- If co::t1 -> t2, p::t2,
-- then (CoPat co p) :: t1
- (Pat id) -- No nested location reqd
- Type
+ (Pat id) -- Why not LPat? Ans: existing locn will do
+ Type -- Type of whole pattern, t1
+ -- During desugaring a (CoPat co pat) turns into a cast with 'co' on
+ -- the scrutinee, followed by a match on 'pat'
+\end{code}
+
+HsConDetails is use for patterns/expressions *and* for data type declarations
+
+\begin{code}
+data HsConDetails arg rec
+ = PrefixCon [arg] -- C p1 p2 p3
+ | RecCon rec -- C { x = p1, y = p2 }
+ | InfixCon arg arg -- p1 `C` p2
+
+type HsConPatDetails id = HsConDetails (LPat id) (HsRecFields id (LPat id))
+
+hsConPatArgs :: HsConPatDetails id -> [LPat id]
+hsConPatArgs (PrefixCon ps) = ps
+hsConPatArgs (RecCon fs) = map hsRecFieldArg (rec_flds fs)
+hsConPatArgs (InfixCon p1 p2) = [p1,p2]
\end{code}
-HsConDetails is use both for patterns and for data type declarations
+However HsRecFields is used only for patterns and expressions
+(not data type declarations)
\begin{code}
-data HsConDetails id arg
- = PrefixCon [arg] -- C p1 p2 p3
- | RecCon [(Located id, arg)] -- C { x = p1, y = p2 }
- | InfixCon arg arg -- p1 `C` p2
-
-hsConArgs :: HsConDetails id arg -> [arg]
-hsConArgs (PrefixCon ps) = ps
-hsConArgs (RecCon fs) = map snd fs
-hsConArgs (InfixCon p1 p2) = [p1,p2]
+data HsRecFields id arg -- A bunch of record fields
+ -- { x = 3, y = True }
+ -- Used for both expressiona and patterns
+ = HsRecFields { rec_flds :: [HsRecField id arg],
+ rec_dotdot :: Maybe Int }
+ -- Nothing => the normal case
+ -- Just n => the group uses ".." notation,
+ -- and the first n elts of rec_flds
+ -- were the user-written ones
+ -- (In the latter case, the remaining elts of
+ -- rec_flds are the non-user-written ones)
+
+data HsRecField id arg = HsRecField {
+ hsRecFieldId :: Located id,
+ hsRecFieldArg :: arg,
+ hsRecPun :: Bool -- Note [Punning]
+ }
+
+-- Note [Punning]
+-- ~~~~~~~~~~~~~~
+-- If you write T { x, y = v+1 }, the HsRecFields will be
+-- HsRecField x x True ...
+-- HsRecField y (v+1) False ...
+-- That is, for "punned" field x is immediately expanded to x=x
+-- but with a punning flag so we can detect it later
+-- (e.g. when pretty printing)
+
+hsRecFields :: HsRecFields id arg -> [id]
+hsRecFields rbinds = map (unLoc . hsRecFieldId) (rec_flds rbinds)
\end{code}
pprPat (NPat l (Just _) _ _) = char '-' <> ppr l
pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
pprPat (TypePat ty) = ptext SLIT("{|") <> ppr ty <> ptext SLIT("|}")
-pprPat (CoPat co pat _) = parens (ppr co) <+> ptext SLIT("`cast`") <+> ppr pat
+pprPat (CoPat co pat _) = parens (pprHsWrapper (ppr pat) co)
pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
-pprPat (DictPat ds ms) = parens (sep [ptext SLIT("{-dict-}"),
- brackets (interpp'SP ds),
- brackets (interpp'SP ms)])
pprUserCon c (InfixCon p1 p2) = ppr p1 <+> ppr c <+> ppr p2
pprUserCon c details = ppr c <+> pprConArgs details
pprConArgs (PrefixCon pats) = interppSP pats
pprConArgs (InfixCon p1 p2) = interppSP [p1,p2]
-pprConArgs (RecCon rpats) = braces (hsep (punctuate comma (map (pp_rpat) rpats)))
- where
- pp_rpat (v, p) = hsep [ppr v, char '=', ppr p]
-
+pprConArgs (RecCon rpats) = ppr rpats
+
+instance (OutputableBndr id, Outputable arg)
+ => Outputable (HsRecFields id arg) where
+ ppr (HsRecFields { rec_flds = flds, rec_dotdot = Nothing })
+ = braces (fsep (punctuate comma (map ppr flds)))
+ ppr (HsRecFields { rec_flds = flds, rec_dotdot = Just n })
+ = braces (fsep (punctuate comma (map ppr (take n flds) ++ [dotdot])))
+ where
+ dotdot = ptext SLIT("..") <+> ifPprDebug (ppr (drop n flds))
+
+instance (OutputableBndr id, Outputable arg)
+ => Outputable (HsRecField id arg) where
+ ppr (HsRecField { hsRecFieldId = f, hsRecFieldArg = arg,
+ hsRecPun = pun })
+ = ppr f <+> (if pun then empty else equals <+> ppr arg)
-- add parallel array brackets around a document
--
mkCharLitPat :: Char -> OutPat id
mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
-mkCoPat :: ExprCoFn -> OutPat id -> Type -> OutPat id
+mkCoPat :: HsWrapper -> OutPat id -> Type -> OutPat id
mkCoPat co lpat@(L loc pat) ty
- | isIdCoercion co = lpat
+ | isIdHsWrapper co = lpat
| otherwise = L loc (CoPat co pat ty)
\end{code}
isConPat (ListPat {}) = True
isConPat (PArrPat {}) = True
isConPat (TuplePat {}) = True
-isConPat (DictPat ds ms) = (length ds + length ms) > 1
isConPat other = False
isSigPat (SigPatIn _ _) = True
go1 (ConPatIn _ _) = False -- Conservative
go1 (ConPatOut{ pat_con = L _ con, pat_args = details })
= isProductTyCon (dataConTyCon con)
- && all go (hsConArgs details)
+ && all go (hsConPatArgs details)
go1 (LitPat _) = False
go1 (NPat _ _ _ _) = False
go1 (NPlusKPat _ _ _ _) = False
go1 (TypePat _) = panic "isIrrefutableHsPat: type pattern"
- go1 (DictPat _ _) = panic "isIrrefutableHsPat: type pattern"
\end{code}
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