\section[PatSyntax]{Abstract Haskell syntax---patterns}
\begin{code}
+{-# OPTIONS -fno-warn-incomplete-patterns #-}
+-- 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/Commentary/CodingStyle#Warnings
+-- for details
+{-# LANGUAGE DeriveDataTypeable #-}
+
module HsPat (
Pat(..), InPat, OutPat, LPat,
- HsConDetails(..), hsConArgs,
- HsRecField(..), mkRecField,
-
- mkPrefixConPat, mkCharLitPat, mkNilPat, mkCoPat,
+ HsConDetails(..),
+ HsConPatDetails, hsConPatArgs,
+ HsRecFields(..), HsRecField(..), hsRecFields,
- isBangHsBind,
- patsAreAllCons, isConPat, isSigPat, isWildPat,
- patsAreAllLits, isLitPat, isIrrefutableHsPat
- ) where
+ mkPrefixConPat, mkCharLitPat, mkNilPat,
-#include "HsVersions.h"
+ isBangHsBind, isLiftedPatBind,
+ isBangLPat, hsPatNeedsParens,
+ isIrrefutableHsPat,
+ pprParendLPat
+ ) where
-import {-# SOURCE #-} HsExpr ( SyntaxExpr )
+import {-# SOURCE #-} HsExpr (SyntaxExpr, LHsExpr, pprLExpr)
-- friends:
import HsBinds
import HsLit
import HsTypes
-import HsDoc
import BasicTypes
-- others:
import PprCore ( {- instance OutputableBndr TyVar -} )
import Outputable
import Type
import SrcLoc
+import FastString
+-- libraries:
+import Data.Data hiding (TyCon)
+import Data.Maybe
\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
- | LazyPat (LPat id) -- Lazy pattern
+ | LazyPat (LPat id) -- Lazy pattern
| AsPat (Located id) (LPat id) -- As pattern
| ParPat (LPat id) -- Parenthesised pattern
- | BangPat (LPat id) -- Bang patterng
+ | BangPat (LPat id) -- Bang pattern
------------ Lists, tuples, arrays ---------------
| ListPat [LPat id] -- Syntactic list
------------ Constructor patterns ---------------
| ConPatIn (Located id)
- (HsConDetails id (LPat id))
+ (HsConPatDetails id)
| ConPatOut {
pat_con :: Located DataCon,
- pat_tvs :: [TyVar], -- Existentially bound type variables
- -- 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_tvs :: [TyVar], -- Existentially bound type variables (tyvars only)
+ pat_dicts :: [EvVar], -- Ditto *coercion variables* and *dictionaries*
+ -- One reason for putting coercion variable here, I think,
+ -- is to ensure their kinds are zonked
+ pat_binds :: TcEvBinds, -- Bindings involving those dictionaries
+ pat_args :: HsConPatDetails id,
pat_ty :: Type -- The type of the pattern
}
+ ------------ View patterns ---------------
+ | ViewPat (LHsExpr id)
+ (LPat id)
+ PostTcType -- The overall type of the pattern
+ -- (= the argument type of the view function)
+ -- for hsPatType.
+
+ ------------ Quasiquoted patterns ---------------
+ -- See Note [Quasi-quote overview] in TcSplice
+ | QuasiQuotePat (HsQuasiQuote id)
+
------------ Literal and n+k patterns ---------------
| LitPat HsLit -- Used for *non-overloaded* literal patterns:
-- Int#, Char#, Int, Char, String, etc.
- | NPat (HsOverLit id) -- ALWAYS positive
+ | NPat -- Used for all overloaded literals,
+ -- including overloaded strings with -XOverloadedStrings
+ (HsOverLit id) -- ALWAYS positive
(Maybe (SyntaxExpr id)) -- Just (Name of 'negate') for negative
-- patterns, Nothing otherwise
(SyntaxExpr id) -- Equality checker, of type t->t->Bool
- PostTcType -- Type of the pattern
| NPlusKPat (Located id) -- n+k pattern
(HsOverLit id) -- It'll always be an HsIntegral
(SyntaxExpr id) -- (>=) function, of type t->t->Bool
(SyntaxExpr id) -- Name of '-' (see RnEnv.lookupSyntaxName)
- ------------ Generics ---------------
- | TypePat (LHsType id) -- Type pattern for generic definitions
- -- e.g f{| a+b |} = ...
- -- These show up only in class declarations,
- -- and should be a top-level pattern
-
------------ Pattern type signatures ---------------
| SigPatIn (LPat id) -- Pattern with a type signature
(LHsType id)
| 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 HsWrapper -- If co::t1 -> t2, p::t2,
+ | CoPat HsWrapper -- If co :: t1 ~ t2, p :: t2,
-- then (CoPat co p) :: t1
(Pat id) -- Why not LPat? Ans: existing locn will do
- Type
+ 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'
+ deriving (Data, Typeable)
\end{code}
-HsConDetails is use both for patterns and for data type declarations
+HsConDetails is use for patterns/expressions *and* for data type declarations
\begin{code}
-data HsConDetails id arg
- = PrefixCon [arg] -- C p1 p2 p3
- | RecCon [HsRecField id arg] -- C { x = p1, y = p2 }
- | InfixCon arg arg -- p1 `C` p2
+data HsConDetails arg rec
+ = PrefixCon [arg] -- C p1 p2 p3
+ | RecCon rec -- C { x = p1, y = p2 }
+ | InfixCon arg arg -- p1 `C` p2
+ deriving (Data, Typeable)
+
+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}
+
+However HsRecFields is used only for patterns and expressions
+(not data type declarations)
+
+\begin{code}
+data HsRecFields id arg -- A bunch of record fields
+ -- { x = 3, y = True }
+ -- Used for both expressions and patterns
+ = HsRecFields { rec_flds :: [HsRecField id arg],
+ rec_dotdot :: Maybe Int } -- Note [DotDot fields]
+ deriving (Data, Typeable)
+
+-- Note [DotDot fields]
+-- ~~~~~~~~~~~~~~~~~~~~
+-- The rec_dotdot field means this:
+-- Nothing => the normal case
+-- Just n => the group uses ".." notation,
+--
+-- In the latter case:
+--
+-- *before* renamer: rec_flds are exactly the n user-written fields
+--
+-- *after* renamer: rec_flds includes *all* fields, with
+-- the first 'n' being the user-written ones
+-- and the remainder being 'filled in' implicitly
data HsRecField id arg = HsRecField {
hsRecFieldId :: Located id,
- hsRecFieldArg :: arg,
- hsRecFieldDoc :: Maybe (LHsDoc id)
-}
-
-mkRecField id arg = HsRecField id arg Nothing
+ hsRecFieldArg :: arg, -- Filled in by renamer
+ hsRecPun :: Bool -- Note [Punning]
+ } deriving (Data, Typeable)
+
+-- 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 expanded (in the renamer)
+-- to x=x; but with a punning flag so we can detect it later
+-- (e.g. when pretty printing)
+--
+-- If the original field was qualified, we un-qualify it, thus
+-- T { A.x } means T { A.x = x }
-hsConArgs :: HsConDetails id arg -> [arg]
-hsConArgs (PrefixCon ps) = ps
-hsConArgs (RecCon fs) = map hsRecFieldArg fs
-hsConArgs (InfixCon p1 p2) = [p1,p2]
+hsRecFields :: HsRecFields id arg -> [id]
+hsRecFields rbinds = map (unLoc . hsRecFieldId) (rec_flds rbinds)
\end{code}
-
%************************************************************************
%* *
%* Printing patterns
else
ppr var
+pprParendLPat :: (OutputableBndr name) => LPat name -> SDoc
+pprParendLPat (L _ p) = pprParendPat p
+
+pprParendPat :: (OutputableBndr name) => Pat name -> SDoc
+pprParendPat p | patNeedsParens p = parens (pprPat p)
+ | otherwise = pprPat p
+
+patNeedsParens :: Pat name -> Bool
+patNeedsParens (ConPatIn _ d) = not (null (hsConPatArgs d))
+patNeedsParens (ConPatOut { pat_args = d }) = not (null (hsConPatArgs d))
+patNeedsParens (SigPatIn {}) = True
+patNeedsParens (SigPatOut {}) = True
+patNeedsParens (ViewPat {}) = True
+patNeedsParens (CoPat {}) = True
+patNeedsParens _ = False
+
pprPat :: (OutputableBndr name) => Pat name -> SDoc
pprPat (VarPat var) = pprPatBndr var
-pprPat (VarPatOut var bs) = parens (pprPatBndr var <+> braces (ppr bs))
pprPat (WildPat _) = char '_'
-pprPat (LazyPat pat) = char '~' <> ppr pat
-pprPat (BangPat pat) = char '!' <> ppr pat
-pprPat (AsPat name pat) = parens (hcat [ppr name, char '@', ppr pat])
-pprPat (ParPat pat) = parens (ppr pat)
+pprPat (LazyPat pat) = char '~' <> pprParendLPat pat
+pprPat (BangPat pat) = char '!' <> pprParendLPat pat
+pprPat (AsPat name pat) = hcat [ppr name, char '@', pprParendLPat pat]
+pprPat (ViewPat expr pat _) = hcat [pprLExpr expr, text " -> ", ppr pat]
+pprPat (ParPat pat) = parens (ppr pat)
pprPat (ListPat pats _) = brackets (interpp'SP pats)
pprPat (PArrPat pats _) = pabrackets (interpp'SP pats)
pprPat (TuplePat pats bx _) = tupleParens bx (interpp'SP pats)
if debugStyle sty then -- typechecked Pat in an error message,
-- and we want to make sure it prints nicely
ppr con <+> sep [ hsep (map pprPatBndr tvs) <+> hsep (map pprPatBndr dicts),
- pprLHsBinds binds, pprConArgs details]
+ ppr binds, pprConArgs details]
else pprUserCon con details
-pprPat (LitPat s) = ppr s
-pprPat (NPat l Nothing _ _) = ppr l
-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 (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)])
+pprPat (LitPat s) = ppr s
+pprPat (NPat l Nothing _) = ppr l
+pprPat (NPat l (Just _) _) = char '-' <> ppr l
+pprPat (NPlusKPat n k _ _) = hcat [ppr n, char '+', ppr k]
+pprPat (QuasiQuotePat qq) = ppr qq
+pprPat (CoPat co pat _) = pprHsWrapper (ppr pat) co
+pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
+pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
+pprUserCon :: (Outputable con, OutputableBndr id) => con -> HsConPatDetails id -> SDoc
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 (HsRecField v p d) =
- hsep [ppr d, ppr v, char '=', ppr p]
+pprConArgs :: OutputableBndr id => HsConPatDetails id -> SDoc
+pprConArgs (PrefixCon pats) = sep (map pprParendLPat pats)
+pprConArgs (InfixCon p1 p2) = sep [pprParendLPat p1, pprParendLPat p2]
+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 <+> (ppUnless pun $ equals <+> ppr arg)
-- add parallel array brackets around a document
--
pabrackets :: SDoc -> SDoc
-pabrackets p = ptext SLIT("[:") <> p <> ptext SLIT(":]")
-
-instance (OutputableBndr id, Outputable arg) =>
- Outputable (HsRecField id arg) where
- ppr (HsRecField n ty doc) = ppr n <+> dcolon <+> ppr ty <+> ppr_mbDoc doc
+pabrackets p = ptext (sLit "[:") <> p <> ptext (sLit ":]")
\end{code}
-- Make a vanilla Prefix constructor pattern
mkPrefixConPat dc pats ty
= noLoc $ ConPatOut { pat_con = noLoc dc, pat_tvs = [], pat_dicts = [],
- pat_binds = emptyLHsBinds, pat_args = PrefixCon pats,
+ pat_binds = emptyTcEvBinds, pat_args = PrefixCon pats,
pat_ty = ty }
mkNilPat :: Type -> OutPat id
mkCharLitPat :: Char -> OutPat id
mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy
-
-mkCoPat :: HsWrapper -> OutPat id -> Type -> OutPat id
-mkCoPat co lpat@(L loc pat) ty
- | isIdHsWrapper co = lpat
- | otherwise = L loc (CoPat co pat ty)
\end{code}
The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
\begin{code}
-isWildPat (WildPat _) = True
-isWildPat other = False
-
-patsAreAllCons :: [Pat id] -> Bool
-patsAreAllCons pat_list = all isConPat pat_list
-
-isConPat (AsPat _ pat) = isConPat (unLoc pat)
-isConPat (ConPatIn {}) = True
-isConPat (ConPatOut {}) = True
-isConPat (ListPat {}) = True
-isConPat (PArrPat {}) = True
-isConPat (TuplePat {}) = True
-isConPat (DictPat ds ms) = (length ds + length ms) > 1
-isConPat other = False
-
-isSigPat (SigPatIn _ _) = True
-isSigPat (SigPatOut _ _) = True
-isSigPat other = False
-
-patsAreAllLits :: [Pat id] -> Bool
-patsAreAllLits pat_list = all isLitPat pat_list
-
-isLitPat (AsPat _ pat) = isLitPat (unLoc pat)
-isLitPat (LitPat _) = True
-isLitPat (NPat _ _ _ _) = True
-isLitPat (NPlusKPat _ _ _ _) = True
-isLitPat other = False
+isBangLPat :: LPat id -> Bool
+isBangLPat (L _ (BangPat {})) = True
+isBangLPat (L _ (ParPat p)) = isBangLPat p
+isBangLPat _ = False
isBangHsBind :: HsBind id -> Bool
--- In this module because HsPat is above HsBinds in the import graph
-isBangHsBind (PatBind { pat_lhs = L _ (BangPat p) }) = True
-isBangHsBind bind = False
-
-isIrrefutableHsPat :: LPat id -> Bool
--- This function returns False if it's in doubt; specifically
+-- A pattern binding with an outermost bang
+-- Defined in this module because HsPat is above HsBinds in the import graph
+isBangHsBind (PatBind { pat_lhs = p }) = isBangLPat p
+isBangHsBind _ = False
+
+isLiftedPatBind :: HsBind id -> Bool
+-- A pattern binding with a compound pattern, not just a variable
+-- (I# x) yes
+-- (# a, b #) no, even if a::Int#
+-- x no, even if x::Int#
+-- We want to warn about a missing bang-pattern on the yes's
+isLiftedPatBind (PatBind { pat_lhs = p }) = isLiftedLPat p
+isLiftedPatBind _ = False
+
+isLiftedLPat :: LPat id -> Bool
+isLiftedLPat (L _ (ParPat p)) = isLiftedLPat p
+isLiftedLPat (L _ (BangPat p)) = isLiftedLPat p
+isLiftedLPat (L _ (AsPat _ p)) = isLiftedLPat p
+isLiftedLPat (L _ (TuplePat _ Unboxed _)) = False
+isLiftedLPat (L _ (VarPat {})) = False
+isLiftedLPat (L _ (WildPat {})) = False
+isLiftedLPat _ = True
+
+isIrrefutableHsPat :: OutputableBndr id => LPat id -> Bool
+-- (isIrrefutableHsPat p) is true if matching against p cannot fail,
+-- in the sense of falling through to the next pattern.
+-- (NB: this is not quite the same as the (silly) defn
+-- in 3.17.2 of the Haskell 98 report.)
+--
+-- isIrrefutableHsPat returns False if it's in doubt; specifically
-- on a ConPatIn it doesn't know the size of the constructor family
-- But if it returns True, the pattern is definitely irrefutable
isIrrefutableHsPat pat
= go pat
where
- go (L _ pat) = go1 pat
+ go (L _ pat) = go1 pat
- go1 (WildPat _) = True
- go1 (VarPat _) = True
- go1 (VarPatOut _ _) = True
- go1 (LazyPat pat) = True
+ go1 (WildPat {}) = True
+ go1 (VarPat {}) = True
+ go1 (LazyPat {}) = True
go1 (BangPat pat) = go pat
go1 (CoPat _ pat _) = go1 pat
go1 (ParPat pat) = go pat
go1 (AsPat _ pat) = go pat
+ go1 (ViewPat _ pat _) = go pat
go1 (SigPatIn pat _) = go pat
go1 (SigPatOut pat _) = go pat
go1 (TuplePat pats _ _) = all go pats
- go1 (ListPat pats _) = False
- go1 (PArrPat pats _) = False -- ?
+ go1 (ListPat {}) = False
+ go1 (PArrPat {}) = False -- ?
- go1 (ConPatIn _ _) = False -- Conservative
+ go1 (ConPatIn {}) = False -- Conservative
go1 (ConPatOut{ pat_con = L _ con, pat_args = details })
- = isProductTyCon (dataConTyCon con)
- && all go (hsConArgs details)
-
- go1 (LitPat _) = False
- go1 (NPat _ _ _ _) = False
- go1 (NPlusKPat _ _ _ _) = False
-
- go1 (TypePat _) = panic "isIrrefutableHsPat: type pattern"
- go1 (DictPat _ _) = panic "isIrrefutableHsPat: type pattern"
+ = isJust (tyConSingleDataCon_maybe (dataConTyCon con))
+ -- NB: tyConSingleDataCon_maybe, *not* isProductTyCon, because
+ -- the latter is false of existentials. See Trac #4439
+ && all go (hsConPatArgs details)
+
+ go1 (LitPat {}) = False
+ go1 (NPat {}) = False
+ go1 (NPlusKPat {}) = False
+
+ go1 (QuasiQuotePat {}) = urk pat -- Gotten rid of by renamer, before
+ -- isIrrefutablePat is called
+
+ urk pat = pprPanic "isIrrefutableHsPat:" (ppr pat)
+
+hsPatNeedsParens :: Pat a -> Bool
+hsPatNeedsParens (WildPat {}) = False
+hsPatNeedsParens (VarPat {}) = False
+hsPatNeedsParens (LazyPat {}) = False
+hsPatNeedsParens (BangPat {}) = False
+hsPatNeedsParens (CoPat {}) = True
+hsPatNeedsParens (ParPat {}) = False
+hsPatNeedsParens (AsPat {}) = False
+hsPatNeedsParens (ViewPat {}) = True
+hsPatNeedsParens (SigPatIn {}) = True
+hsPatNeedsParens (SigPatOut {}) = True
+hsPatNeedsParens (TuplePat {}) = False
+hsPatNeedsParens (ListPat {}) = False
+hsPatNeedsParens (PArrPat {}) = False
+hsPatNeedsParens (ConPatIn _ ds) = conPatNeedsParens ds
+hsPatNeedsParens (ConPatOut {}) = True
+hsPatNeedsParens (LitPat {}) = False
+hsPatNeedsParens (NPat {}) = False
+hsPatNeedsParens (NPlusKPat {}) = True
+hsPatNeedsParens (QuasiQuotePat {}) = True
+
+conPatNeedsParens :: HsConDetails a b -> Bool
+conPatNeedsParens (PrefixCon args) = not (null args)
+conPatNeedsParens (InfixCon {}) = False
+conPatNeedsParens (RecCon {}) = False
\end{code}
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