% % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \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(..), HsConPatDetails, hsConPatArgs, HsRecFields(..), HsRecField(..), hsRecFields, mkPrefixConPat, mkCharLitPat, mkNilPat, mkCoPat, mkCoPatCoI, isBangHsBind, hsPatNeedsParens, patsAreAllCons, isConPat, isSigPat, isWildPat, patsAreAllLits, isLitPat, isIrrefutableHsPat, pprParendLPat ) where import {-# SOURCE #-} HsExpr (SyntaxExpr, LHsExpr, pprLExpr) -- friends: import HsBinds import HsLit import HsTypes import BasicTypes -- others: import Coercion import PprCore ( {- instance OutputableBndr TyVar -} ) import TysWiredIn import Var import DataCon import TyCon import Outputable import Type import SrcLoc import FastString -- libraries: import Data.Data hiding (TyCon) \end{code} \begin{code} type InPat id = LPat id -- No 'Out' constructors type OutPat id = LPat id -- No 'In' constructors type LPat id = Located (Pat id) 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 | AsPat (Located id) (LPat id) -- As pattern | ParPat (LPat id) -- Parenthesised pattern | BangPat (LPat id) -- Bang pattern ------------ Lists, tuples, arrays --------------- | ListPat [LPat id] -- Syntactic list PostTcType -- The type of the elements | TuplePat [LPat id] -- Tuple Boxity -- UnitPat is TuplePat [] PostTcType -- You might think that the PostTcType was redundant, 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 | PArrPat [LPat id] -- Syntactic parallel array PostTcType -- The type of the elements ------------ Constructor patterns --------------- | ConPatIn (Located id) (HsConPatDetails id) | ConPatOut { pat_con :: Located DataCon, pat_tvs :: [TyVar], -- Existentially bound type variables (tyvars only) pat_dicts :: [id], -- Ditto *coercion variables* and *dictionaries* -- One reason for putting coercion variable here, I think, -- is to ensure their kinds are zonked pat_binds :: DictBinds id, -- 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 (Maybe (SyntaxExpr id)) -- Just (Name of 'negate') for negative -- patterns, Nothing otherwise (SyntaxExpr id) -- Equality checker, of type t->t->Bool | 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 ------------ Pattern coercions (translation only) --------------- | 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 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 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 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, -- 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 } hsRecFields :: HsRecFields id arg -> [id] hsRecFields rbinds = map (unLoc . hsRecFieldId) (rec_flds rbinds) \end{code} %************************************************************************ %* * %* Printing patterns %* * %************************************************************************ \begin{code} instance (OutputableBndr name) => Outputable (Pat name) 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 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) = pprPatBndr var <+> braces (ppr bs) pprPat (WildPat _) = char '_' 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) pprPat (ConPatIn con details) = pprUserCon con details pprPat (ConPatOut { pat_con = con, pat_tvs = tvs, pat_dicts = dicts, pat_binds = binds, pat_args = details }) = getPprStyle $ \ sty -> -- Tiresome; in TcBinds.tcRhs we print out a 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] 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 (QuasiQuotePat qq) = ppr qq pprPat (TypePat ty) = ptext (sLit "{|") <> ppr ty <> ptext (sLit "|}") 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 :: 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 ":]") \end{code} %************************************************************************ %* * %* Building patterns %* * %************************************************************************ \begin{code} mkPrefixConPat :: DataCon -> [OutPat id] -> Type -> OutPat id -- 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_ty = ty } mkNilPat :: Type -> OutPat id mkNilPat ty = mkPrefixConPat nilDataCon [] ty mkCharLitPat :: Char -> OutPat id mkCharLitPat c = mkPrefixConPat charDataCon [noLoc $ LitPat (HsCharPrim c)] charTy mkCoPat :: HsWrapper -> Pat id -> Type -> Pat id mkCoPat co pat ty | isIdHsWrapper co = pat | otherwise = CoPat co pat ty mkCoPatCoI :: CoercionI -> Pat id -> Type -> Pat id mkCoPatCoI IdCo pat _ = pat mkCoPatCoI (ACo co) pat ty = mkCoPat (WpCast co) pat ty \end{code} %************************************************************************ %* * %* 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. \begin{code} isWildPat :: Pat id -> Bool isWildPat (WildPat _) = True isWildPat _ = False patsAreAllCons :: [Pat id] -> Bool patsAreAllCons pat_list = all isConPat pat_list isConPat :: Pat id -> Bool isConPat (AsPat _ pat) = isConPat (unLoc pat) isConPat (ConPatIn {}) = True isConPat (ConPatOut {}) = True isConPat (ListPat {}) = True isConPat (PArrPat {}) = True isConPat (TuplePat {}) = True isConPat _ = False isSigPat :: Pat id -> Bool isSigPat (SigPatIn _ _) = True isSigPat (SigPatOut _ _) = True isSigPat _ = False patsAreAllLits :: [Pat id] -> Bool patsAreAllLits pat_list = all isLitPat pat_list isLitPat :: Pat id -> Bool isLitPat (AsPat _ pat) = isLitPat (unLoc pat) isLitPat (LitPat _) = True isLitPat (NPat _ _ _) = True isLitPat (NPlusKPat _ _ _ _) = True isLitPat _ = False isBangHsBind :: HsBind id -> Bool -- In this module because HsPat is above HsBinds in the import graph isBangHsBind (PatBind { pat_lhs = L _ (BangPat _) }) = True isBangHsBind _ = False 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 go1 (WildPat {}) = True go1 (VarPat {}) = True go1 (VarPatOut {}) = 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 {}) = False go1 (PArrPat {}) = False -- ? go1 (ConPatIn {}) = False -- Conservative go1 (ConPatOut{ pat_con = L _ con, pat_args = details }) = isProductTyCon (dataConTyCon con) && 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 go1 (TypePat {}) = urk pat urk pat = pprPanic "isIrrefutableHsPat:" (ppr pat) hsPatNeedsParens :: Pat a -> Bool hsPatNeedsParens (WildPat {}) = False hsPatNeedsParens (VarPat {}) = False hsPatNeedsParens (VarPatOut {}) = True 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 hsPatNeedsParens (TypePat {}) = False conPatNeedsParens :: HsConDetails a b -> Bool conPatNeedsParens (PrefixCon args) = not (null args) conPatNeedsParens (InfixCon {}) = False conPatNeedsParens (RecCon {}) = False \end{code}