{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 \section[PatSyntax]{Abstract Haskell syntax---patterns} -} {-# LANGUAGE DeriveDataTypeable #-} {-# LANGUAGE DeriveFunctor #-} {-# LANGUAGE DeriveFoldable #-} {-# LANGUAGE DeriveTraversable #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE UndecidableInstances #-} -- Note [Pass sensitive types] -- in module PlaceHolder {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE ViewPatterns #-} {-# LANGUAGE FlexibleInstances #-} module HsPat ( Pat(..), InPat, OutPat, LPat, ListPatTc(..), HsConPatDetails, hsConPatArgs, HsRecFields(..), HsRecField'(..), LHsRecField', HsRecField, LHsRecField, HsRecUpdField, LHsRecUpdField, hsRecFields, hsRecFieldSel, hsRecFieldId, hsRecFieldsArgs, hsRecUpdFieldId, hsRecUpdFieldOcc, hsRecUpdFieldRdr, mkPrefixConPat, mkCharLitPat, mkNilPat, looksLazyPatBind, isBangedLPat, patNeedsParens, parenthesizePat, isIrrefutableHsPat, collectEvVarsPat, collectEvVarsPats, pprParendLPat, pprConArgs ) where import GhcPrelude import {-# SOURCE #-} HsExpr (SyntaxExpr, LHsExpr, HsSplice, pprLExpr, pprSplice) -- friends: import HsBinds import HsLit import HsExtension import HsTypes import TcEvidence import BasicTypes -- others: import PprCore ( {- instance OutputableBndr TyVar -} ) import TysWiredIn import Var import RdrName ( RdrName ) import ConLike import DataCon import TyCon import Outputable import Type import SrcLoc import Bag -- collect ev vars from pats import DynFlags( gopt, GeneralFlag(..) ) import Maybes -- libraries: import Data.Data hiding (TyCon,Fixity) type InPat p = LPat p -- No 'Out' constructors type OutPat p = LPat p -- No 'In' constructors type LPat p = Pat p -- | Pattern -- -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnBang' -- For details on above see note [Api annotations] in ApiAnnotation data Pat p = ------------ Simple patterns --------------- WildPat (XWildPat p) -- ^ Wildcard Pattern -- The sole reason for a type on a WildPat is to -- support hsPatType :: Pat Id -> Type -- AZ:TODO above comment needs to be updated | VarPat (XVarPat p) (Located (IdP p)) -- ^ Variable Pattern -- See Note [Located RdrNames] in HsExpr | LazyPat (XLazyPat p) (LPat p) -- ^ Lazy Pattern -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnTilde' -- For details on above see note [Api annotations] in ApiAnnotation | AsPat (XAsPat p) (Located (IdP p)) (LPat p) -- ^ As pattern -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnAt' -- For details on above see note [Api annotations] in ApiAnnotation | ParPat (XParPat p) (LPat p) -- ^ Parenthesised pattern -- See Note [Parens in HsSyn] in HsExpr -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'('@, -- 'ApiAnnotation.AnnClose' @')'@ -- For details on above see note [Api annotations] in ApiAnnotation | BangPat (XBangPat p) (LPat p) -- ^ Bang pattern -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnBang' -- For details on above see note [Api annotations] in ApiAnnotation ------------ Lists, tuples, arrays --------------- | ListPat (XListPat p) [LPat p] -- For OverloadedLists a Just (ty,fn) gives -- overall type of the pattern, and the toList -- function to convert the scrutinee to a list value -- ^ Syntactic List -- -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'['@, -- 'ApiAnnotation.AnnClose' @']'@ -- For details on above see note [Api annotations] in ApiAnnotation | TuplePat (XTuplePat p) -- after typechecking, holds the types of the tuple components [LPat p] -- Tuple sub-patterns Boxity -- UnitPat is TuplePat [] -- You might think that the post typechecking Type was redundant, -- because we can get the pattern type by getting the types of the -- sub-patterns. -- But it's essential -- data T a where -- T1 :: Int -> T Int -- f :: (T a, a) -> Int -- f (T1 x, z) = z -- When desugaring, we must generate -- f = /\a. \v::a. case v of (t::T a, w::a) -> -- case t of (T1 (x::Int)) -> -- Note the (w::a), NOT (w::Int), because we have not yet -- refined 'a' to Int. So we must know that the second component -- of the tuple is of type 'a' not Int. See selectMatchVar -- (June 14: I'm not sure this comment is right; the sub-patterns -- will be wrapped in CoPats, no?) -- ^ Tuple sub-patterns -- -- - 'ApiAnnotation.AnnKeywordId' : -- 'ApiAnnotation.AnnOpen' @'('@ or @'(#'@, -- 'ApiAnnotation.AnnClose' @')'@ or @'#)'@ | SumPat (XSumPat p) -- PlaceHolder before typechecker, filled in -- afterwards with the types of the -- alternative (LPat p) -- Sum sub-pattern ConTag -- Alternative (one-based) Arity -- Arity (INVARIANT: ≥ 2) -- ^ Anonymous sum pattern -- -- - 'ApiAnnotation.AnnKeywordId' : -- 'ApiAnnotation.AnnOpen' @'(#'@, -- 'ApiAnnotation.AnnClose' @'#)'@ -- For details on above see note [Api annotations] in ApiAnnotation ------------ Constructor patterns --------------- | ConPatIn (Located (IdP p)) (HsConPatDetails p) -- ^ Constructor Pattern In | ConPatOut { pat_con :: Located ConLike, pat_arg_tys :: [Type], -- The universal arg types, 1-1 with the universal -- tyvars of the constructor/pattern synonym -- Use (conLikeResTy pat_con pat_arg_tys) to get -- the type of the pattern pat_tvs :: [TyVar], -- Existentially bound type variables -- in correctly-scoped order e.g. [k:*, x:k] 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 p, pat_wrap :: HsWrapper -- Extra wrapper to pass to the matcher -- Only relevant for pattern-synonyms; -- ignored for data cons } -- ^ Constructor Pattern Out ------------ View patterns --------------- -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnRarrow' -- For details on above see note [Api annotations] in ApiAnnotation | ViewPat (XViewPat p) -- The overall type of the pattern -- (= the argument type of the view function) -- for hsPatType. (LHsExpr p) (LPat p) -- ^ View Pattern ------------ Pattern splices --------------- -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'$('@ -- 'ApiAnnotation.AnnClose' @')'@ -- For details on above see note [Api annotations] in ApiAnnotation | SplicePat (XSplicePat p) (HsSplice p) -- ^ Splice Pattern (Includes quasi-quotes) ------------ Literal and n+k patterns --------------- | LitPat (XLitPat p) (HsLit p) -- ^ Literal Pattern -- Used for *non-overloaded* literal patterns: -- Int#, Char#, Int, Char, String, etc. | NPat -- Natural Pattern -- Used for all overloaded literals, -- including overloaded strings with -XOverloadedStrings (XNPat p) -- Overall type of pattern. Might be -- different than the literal's type -- if (==) or negate changes the type (Located (HsOverLit p)) -- ALWAYS positive (Maybe (SyntaxExpr p)) -- Just (Name of 'negate') for -- negative patterns, Nothing -- otherwise (SyntaxExpr p) -- Equality checker, of type t->t->Bool -- ^ Natural Pattern -- -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnVal' @'+'@ -- For details on above see note [Api annotations] in ApiAnnotation | NPlusKPat (XNPlusKPat p) -- Type of overall pattern (Located (IdP p)) -- n+k pattern (Located (HsOverLit p)) -- It'll always be an HsIntegral (HsOverLit p) -- See Note [NPlusK patterns] in TcPat -- NB: This could be (PostTc ...), but that induced a -- a new hs-boot file. Not worth it. (SyntaxExpr p) -- (>=) function, of type t1->t2->Bool (SyntaxExpr p) -- Name of '-' (see RnEnv.lookupSyntaxName) -- ^ n+k pattern ------------ Pattern type signatures --------------- -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDcolon' -- For details on above see note [Api annotations] in ApiAnnotation | SigPat (XSigPat p) -- After typechecker: Type (LPat p) -- Pattern with a type signature (LHsSigWcType (NoGhcTc p)) -- Signature can bind both -- kind and type vars -- ^ Pattern with a type signature ------------ Pattern coercions (translation only) --------------- | CoPat (XCoPat p) HsWrapper -- Coercion Pattern -- If co :: t1 ~ t2, p :: t2, -- then (CoPat co p) :: t1 (Pat p) -- 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' -- ^ Coercion Pattern -- | Trees that Grow extension point for new constructors | XPat (XXPat p) -- --------------------------------------------------------------------- data ListPatTc = ListPatTc Type -- The type of the elements (Maybe (Type, SyntaxExpr GhcTc)) -- For rebindable syntax type instance XWildPat GhcPs = NoExt type instance XWildPat GhcRn = NoExt type instance XWildPat GhcTc = Type type instance XVarPat (GhcPass _) = NoExt type instance XLazyPat (GhcPass _) = NoExt type instance XAsPat (GhcPass _) = NoExt type instance XParPat (GhcPass _) = NoExt type instance XBangPat (GhcPass _) = NoExt -- Note: XListPat cannot be extended when using GHC 8.0.2 as the bootstrap -- compiler, as it triggers https://ghc.haskell.org/trac/ghc/ticket/14396 for -- `SyntaxExpr` type instance XListPat GhcPs = NoExt type instance XListPat GhcRn = Maybe (SyntaxExpr GhcRn) type instance XListPat GhcTc = ListPatTc type instance XTuplePat GhcPs = NoExt type instance XTuplePat GhcRn = NoExt type instance XTuplePat GhcTc = [Type] type instance XSumPat GhcPs = NoExt type instance XSumPat GhcRn = NoExt type instance XSumPat GhcTc = [Type] type instance XViewPat GhcPs = NoExt type instance XViewPat GhcRn = NoExt type instance XViewPat GhcTc = Type type instance XSplicePat (GhcPass _) = NoExt type instance XLitPat (GhcPass _) = NoExt type instance XNPat GhcPs = NoExt type instance XNPat GhcRn = NoExt type instance XNPat GhcTc = Type type instance XNPlusKPat GhcPs = NoExt type instance XNPlusKPat GhcRn = NoExt type instance XNPlusKPat GhcTc = Type type instance XSigPat GhcPs = NoExt type instance XSigPat GhcRn = NoExt type instance XSigPat GhcTc = Type type instance XCoPat (GhcPass _) = NoExt type instance XXPat (GhcPass p) = Located (Pat (GhcPass p)) {- ************************************************************************ * * * HasSrcSpan Instance * * ************************************************************************ -} type instance SrcSpanLess (LPat (GhcPass p)) = Pat (GhcPass p) instance HasSrcSpan (LPat (GhcPass p)) where -- NB: The following chooses the behaviour of the outer location -- wrapper replacing the inner ones. composeSrcSpan (L sp p) = if sp == noSrcSpan then p else XPat (L sp (stripSrcSpanPat p)) -- NB: The following only returns the top-level location, if any. decomposeSrcSpan (XPat (L sp p)) = L sp (stripSrcSpanPat p) decomposeSrcSpan p = L noSrcSpan p stripSrcSpanPat :: LPat (GhcPass p) -> Pat (GhcPass p) stripSrcSpanPat (XPat (L _ p)) = stripSrcSpanPat p stripSrcSpanPat p = p -- --------------------------------------------------------------------- -- | Haskell Constructor Pattern Details type HsConPatDetails p = HsConDetails (LPat p) (HsRecFields p (LPat p)) hsConPatArgs :: HsConPatDetails p -> [LPat p] hsConPatArgs (PrefixCon ps) = ps hsConPatArgs (RecCon fs) = map (hsRecFieldArg . unLoc) (rec_flds fs) hsConPatArgs (InfixCon p1 p2) = [p1,p2] -- | Haskell Record Fields -- -- HsRecFields is used only for patterns and expressions (not data type -- declarations) data HsRecFields p arg -- A bunch of record fields -- { x = 3, y = True } -- Used for both expressions and patterns = HsRecFields { rec_flds :: [LHsRecField p arg], rec_dotdot :: Maybe Int } -- Note [DotDot fields] deriving (Functor, Foldable, Traversable) -- 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 -- | Located Haskell Record Field type LHsRecField' p arg = Located (HsRecField' p arg) -- | Located Haskell Record Field type LHsRecField p arg = Located (HsRecField p arg) -- | Located Haskell Record Update Field type LHsRecUpdField p = Located (HsRecUpdField p) -- | Haskell Record Field type HsRecField p arg = HsRecField' (FieldOcc p) arg -- | Haskell Record Update Field type HsRecUpdField p = HsRecField' (AmbiguousFieldOcc p) (LHsExpr p) -- | Haskell Record Field -- -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnEqual', -- -- For details on above see note [Api annotations] in ApiAnnotation data HsRecField' id arg = HsRecField { hsRecFieldLbl :: Located id, hsRecFieldArg :: arg, -- ^ Filled in by renamer when punning hsRecPun :: Bool -- ^ Note [Punning] } deriving (Data, Functor, Foldable, Traversable) -- 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 } -- Note [HsRecField and HsRecUpdField] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- A HsRecField (used for record construction and pattern matching) -- contains an unambiguous occurrence of a field (i.e. a FieldOcc). -- We can't just store the Name, because thanks to -- DuplicateRecordFields this may not correspond to the label the user -- wrote. -- -- A HsRecUpdField (used for record update) contains a potentially -- ambiguous occurrence of a field (an AmbiguousFieldOcc). The -- renamer will fill in the selector function if it can, but if the -- selector is ambiguous the renamer will defer to the typechecker. -- After the typechecker, a unique selector will have been determined. -- -- The renamer produces an Unambiguous result if it can, rather than -- just doing the lookup in the typechecker, so that completely -- unambiguous updates can be represented by 'DsMeta.repUpdFields'. -- -- For example, suppose we have: -- -- data S = MkS { x :: Int } -- data T = MkT { x :: Int } -- -- f z = (z { x = 3 }) :: S -- -- The parsed HsRecUpdField corresponding to the record update will have: -- -- hsRecFieldLbl = Unambiguous "x" NoExt :: AmbiguousFieldOcc RdrName -- -- After the renamer, this will become: -- -- hsRecFieldLbl = Ambiguous "x" NoExt :: AmbiguousFieldOcc Name -- -- (note that the Unambiguous constructor is not type-correct here). -- The typechecker will determine the particular selector: -- -- hsRecFieldLbl = Unambiguous "x" $sel:x:MkS :: AmbiguousFieldOcc Id -- -- See also Note [Disambiguating record fields] in TcExpr. hsRecFields :: HsRecFields p arg -> [XCFieldOcc p] hsRecFields rbinds = map (unLoc . hsRecFieldSel . unLoc) (rec_flds rbinds) -- Probably won't typecheck at once, things have changed :/ hsRecFieldsArgs :: HsRecFields p arg -> [arg] hsRecFieldsArgs rbinds = map (hsRecFieldArg . unLoc) (rec_flds rbinds) hsRecFieldSel :: HsRecField pass arg -> Located (XCFieldOcc pass) hsRecFieldSel = fmap extFieldOcc . hsRecFieldLbl hsRecFieldId :: HsRecField GhcTc arg -> Located Id hsRecFieldId = hsRecFieldSel hsRecUpdFieldRdr :: HsRecUpdField (GhcPass p) -> Located RdrName hsRecUpdFieldRdr = fmap rdrNameAmbiguousFieldOcc . hsRecFieldLbl hsRecUpdFieldId :: HsRecField' (AmbiguousFieldOcc GhcTc) arg -> Located Id hsRecUpdFieldId = fmap extFieldOcc . hsRecUpdFieldOcc hsRecUpdFieldOcc :: HsRecField' (AmbiguousFieldOcc GhcTc) arg -> LFieldOcc GhcTc hsRecUpdFieldOcc = fmap unambiguousFieldOcc . hsRecFieldLbl {- ************************************************************************ * * * Printing patterns * * ************************************************************************ -} instance (p ~ GhcPass pass, OutputableBndrId p) => Outputable (Pat p) where ppr = pprPat pprPatBndr :: OutputableBndr name => name -> SDoc pprPatBndr var -- Print with type info if -dppr-debug is on = getPprStyle $ \ sty -> if debugStyle sty then parens (pprBndr LambdaBind var) -- Could pass the site to pprPat -- but is it worth it? else pprPrefixOcc var pprParendLPat :: (OutputableBndrId (GhcPass p)) => PprPrec -> LPat (GhcPass p) -> SDoc pprParendLPat p = pprParendPat p . unLoc pprParendPat :: (OutputableBndrId (GhcPass p)) => PprPrec -> Pat (GhcPass p) -> SDoc pprParendPat p pat = sdocWithDynFlags $ \ dflags -> if need_parens dflags pat then parens (pprPat pat) else pprPat pat where need_parens dflags pat | CoPat {} <- pat = gopt Opt_PrintTypecheckerElaboration dflags | otherwise = patNeedsParens p pat -- For a CoPat we need parens if we are going to show it, which -- we do if -fprint-typechecker-elaboration is on (c.f. pprHsWrapper) -- But otherwise the CoPat is discarded, so it -- is the pattern inside that matters. Sigh. pprPat :: (OutputableBndrId (GhcPass p)) => Pat (GhcPass p) -> SDoc pprPat (VarPat _ lvar) = pprPatBndr (unLoc lvar) pprPat (WildPat _) = char '_' pprPat (LazyPat _ pat) = char '~' <> pprParendLPat appPrec pat pprPat (BangPat _ pat) = char '!' <> pprParendLPat appPrec pat pprPat (AsPat _ name pat) = hcat [pprPrefixOcc (unLoc name), char '@', pprParendLPat appPrec pat] pprPat (ViewPat _ expr pat) = hcat [pprLExpr expr, text " -> ", ppr pat] pprPat (ParPat _ pat) = parens (ppr pat) 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 (SplicePat _ splice) = pprSplice splice pprPat (CoPat _ co pat _) = pprHsWrapper co $ \parens -> if parens then pprParendPat appPrec pat else pprPat pat pprPat (SigPat _ pat ty) = ppr pat <+> dcolon <+> ppr ty pprPat (ListPat _ pats) = brackets (interpp'SP pats) pprPat (TuplePat _ pats bx) = tupleParens (boxityTupleSort bx) (pprWithCommas ppr pats) pprPat (SumPat _ pat alt arity) = sumParens (pprAlternative ppr pat alt arity) pprPat (ConPatIn con details) = pprUserCon (unLoc con) details pprPat (ConPatOut { pat_con = con , pat_tvs = tvs , pat_dicts = dicts , pat_binds = binds , pat_args = details }) = sdocWithDynFlags $ \dflags -> -- Tiresome; in TcBinds.tcRhs we print out a -- typechecked Pat in an error message, -- and we want to make sure it prints nicely if gopt Opt_PrintTypecheckerElaboration dflags then ppr con <> braces (sep [ hsep (map pprPatBndr (tvs ++ dicts)) , ppr binds]) <+> pprConArgs details else pprUserCon (unLoc con) details pprPat (XPat x) = ppr x pprUserCon :: (OutputableBndr con, OutputableBndrId (GhcPass p)) => con -> HsConPatDetails (GhcPass p) -> SDoc pprUserCon c (InfixCon p1 p2) = ppr p1 <+> pprInfixOcc c <+> ppr p2 pprUserCon c details = pprPrefixOcc c <+> pprConArgs details pprConArgs :: (OutputableBndrId (GhcPass p)) => HsConPatDetails (GhcPass p) -> SDoc pprConArgs (PrefixCon pats) = sep (map (pprParendLPat appPrec) pats) pprConArgs (InfixCon p1 p2) = sep [ pprParendLPat appPrec p1 , pprParendLPat appPrec p2 ] pprConArgs (RecCon rpats) = ppr rpats instance (Outputable arg) => Outputable (HsRecFields p 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 = text ".." <+> whenPprDebug (ppr (drop n flds)) instance (Outputable p, Outputable arg) => Outputable (HsRecField' p arg) where ppr (HsRecField { hsRecFieldLbl = f, hsRecFieldArg = arg, hsRecPun = pun }) = ppr f <+> (ppUnless pun $ equals <+> ppr arg) {- ************************************************************************ * * * Building patterns * * ************************************************************************ -} mkPrefixConPat :: DataCon -> [OutPat (GhcPass p)] -> [Type] -> OutPat (GhcPass p) -- Make a vanilla Prefix constructor pattern mkPrefixConPat dc pats tys = noLoc $ ConPatOut { pat_con = noLoc (RealDataCon dc) , pat_tvs = [] , pat_dicts = [] , pat_binds = emptyTcEvBinds , pat_args = PrefixCon pats , pat_arg_tys = tys , pat_wrap = idHsWrapper } mkNilPat :: Type -> OutPat (GhcPass p) mkNilPat ty = mkPrefixConPat nilDataCon [] [ty] mkCharLitPat :: SourceText -> Char -> OutPat (GhcPass p) mkCharLitPat src c = mkPrefixConPat charDataCon [noLoc $ LitPat NoExt (HsCharPrim src c)] [] {- ************************************************************************ * * * Predicates for checking things about pattern-lists in EquationInfo * * * ************************************************************************ \subsection[Pat-list-predicates]{Look for interesting things in patterns} Unlike in the Wadler chapter, where patterns are either ``variables'' or ``constructors,'' here we distinguish between: \begin{description} \item[unfailable:] Patterns that cannot fail to match: variables, wildcards, and lazy patterns. These are the irrefutable patterns; the two other categories are refutable patterns. \item[constructor:] A non-literal constructor pattern (see next category). \item[literal patterns:] At least the numeric ones may be overloaded. \end{description} A pattern is in {\em exactly one} of the above three categories; `as' patterns are treated specially, of course. The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are. -} isBangedLPat :: LPat (GhcPass p) -> Bool isBangedLPat = isBangedPat . unLoc isBangedPat :: Pat (GhcPass p) -> Bool isBangedPat (ParPat _ p) = isBangedLPat p isBangedPat (BangPat {}) = True isBangedPat _ = False looksLazyPatBind :: HsBind (GhcPass p) -> Bool -- Returns True of anything *except* -- a StrictHsBind (as above) or -- a VarPat -- In particular, returns True of a pattern binding with a compound pattern, like (I# x) -- Looks through AbsBinds looksLazyPatBind (PatBind { pat_lhs = p }) = looksLazyLPat p looksLazyPatBind (AbsBinds { abs_binds = binds }) = anyBag (looksLazyPatBind . unLoc) binds looksLazyPatBind _ = False looksLazyLPat :: LPat (GhcPass p) -> Bool looksLazyLPat = looksLazyPat . unLoc looksLazyPat :: Pat (GhcPass p) -> Bool looksLazyPat (ParPat _ p) = looksLazyLPat p looksLazyPat (AsPat _ _ p) = looksLazyLPat p looksLazyPat (BangPat {}) = False looksLazyPat (VarPat {}) = False looksLazyPat (WildPat {}) = False looksLazyPat _ = True isIrrefutableHsPat :: (OutputableBndrId (GhcPass p)) => LPat (GhcPass p) -> 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.) -- -- WARNING: isIrrefutableHsPat returns False if it's in doubt. -- Specifically on a ConPatIn, which is what it sees for a -- (LPat Name) in the renamer, it doesn't know the size of the -- constructor family, so it returns False. Result: only -- tuple patterns are considered irrefuable at the renamer stage. -- -- But if it returns True, the pattern is definitely irrefutable isIrrefutableHsPat = goL where goL = go . unLoc go (WildPat {}) = True go (VarPat {}) = True go (LazyPat {}) = True go (BangPat _ pat) = goL pat go (CoPat _ _ pat _) = go pat go (ParPat _ pat) = goL pat go (AsPat _ _ pat) = goL pat go (ViewPat _ _ pat) = goL pat go (SigPat _ pat _) = goL pat go (TuplePat _ pats _) = all goL pats go (SumPat {}) = False -- See Note [Unboxed sum patterns aren't irrefutable] go (ListPat {}) = False go (ConPatIn {}) = False -- Conservative go (ConPatOut { pat_con = (dL->L _ (RealDataCon con)) , pat_args = details }) = isJust (tyConSingleDataCon_maybe (dataConTyCon con)) -- NB: tyConSingleDataCon_maybe, *not* isProductTyCon, because -- the latter is false of existentials. See Trac #4439 && all goL (hsConPatArgs details) go (ConPatOut { pat_con = (dL->L _ (PatSynCon _pat)) }) = False -- Conservative go (ConPatOut{}) = panic "ConPatOut:Impossible Match" -- due to #15884 go (LitPat {}) = False go (NPat {}) = False go (NPlusKPat {}) = False -- We conservatively assume that no TH splices are irrefutable -- since we cannot know until the splice is evaluated. go (SplicePat {}) = False go (XPat {}) = False {- Note [Unboxed sum patterns aren't irrefutable] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Unlike unboxed tuples, unboxed sums are *not* irrefutable when used as patterns. A simple example that demonstrates this is from #14228: pattern Just' x = (# x | #) pattern Nothing' = (# | () #) foo x = case x of Nothing' -> putStrLn "nothing" Just' -> putStrLn "just" In foo, the pattern Nothing' (that is, (# x | #)) is certainly not irrefutable, as does not match an unboxed sum value of the same arity—namely, (# | y #) (covered by Just'). In fact, no unboxed sum pattern is irrefutable, since the minimum unboxed sum arity is 2. Failing to mark unboxed sum patterns as non-irrefutable would cause the Just' case in foo to be unreachable, as GHC would mistakenly believe that Nothing' is the only thing that could possibly be matched! -} -- | @'patNeedsParens' p pat@ returns 'True' if the pattern @pat@ needs -- parentheses under precedence @p@. patNeedsParens :: PprPrec -> Pat p -> Bool patNeedsParens p = go where go (NPlusKPat {}) = p > opPrec go (SplicePat {}) = False go (ConPatIn _ ds) = conPatNeedsParens p ds go cp@(ConPatOut {}) = conPatNeedsParens p (pat_args cp) go (SigPat {}) = p >= sigPrec go (ViewPat {}) = True go (CoPat _ _ p _) = go p go (WildPat {}) = False go (VarPat {}) = False go (LazyPat {}) = False go (BangPat {}) = False go (ParPat {}) = False go (AsPat {}) = False go (TuplePat {}) = False go (SumPat {}) = False go (ListPat {}) = False go (LitPat _ l) = hsLitNeedsParens p l go (NPat _ lol _ _) = hsOverLitNeedsParens p (unLoc lol) go (XPat {}) = True -- conservative default -- | @'conPatNeedsParens' p cp@ returns 'True' if the constructor patterns @cp@ -- needs parentheses under precedence @p@. conPatNeedsParens :: PprPrec -> HsConDetails a b -> Bool conPatNeedsParens p = go where go (PrefixCon args) = p >= appPrec && not (null args) go (InfixCon {}) = p >= opPrec go (RecCon {}) = False -- | @'parenthesizePat' p pat@ checks if @'patNeedsParens' p pat@ is true, and -- if so, surrounds @pat@ with a 'ParPat'. Otherwise, it simply returns @pat@. parenthesizePat :: PprPrec -> LPat (GhcPass p) -> LPat (GhcPass p) parenthesizePat p lpat@(dL->L loc pat) | patNeedsParens p pat = cL loc (ParPat NoExt lpat) | otherwise = lpat {- % Collect all EvVars from all constructor patterns -} -- May need to add more cases collectEvVarsPats :: [Pat GhcTc] -> Bag EvVar collectEvVarsPats = unionManyBags . map collectEvVarsPat collectEvVarsLPat :: LPat GhcTc -> Bag EvVar collectEvVarsLPat = collectEvVarsPat . unLoc collectEvVarsPat :: Pat GhcTc -> Bag EvVar collectEvVarsPat pat = case pat of LazyPat _ p -> collectEvVarsLPat p AsPat _ _ p -> collectEvVarsLPat p ParPat _ p -> collectEvVarsLPat p BangPat _ p -> collectEvVarsLPat p ListPat _ ps -> unionManyBags $ map collectEvVarsLPat ps TuplePat _ ps _ -> unionManyBags $ map collectEvVarsLPat ps SumPat _ p _ _ -> collectEvVarsLPat p ConPatOut {pat_dicts = dicts, pat_args = args} -> unionBags (listToBag dicts) $ unionManyBags $ map collectEvVarsLPat $ hsConPatArgs args SigPat _ p _ -> collectEvVarsLPat p CoPat _ _ p _ -> collectEvVarsPat p ConPatIn _ _ -> panic "foldMapPatBag: ConPatIn" _other_pat -> emptyBag