ghc-8.2.2: hsSyn/HsPat.hs
{-
(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 #-}
module HsPat (
Pat(..), InPat, OutPat, LPat,
HsConPatDetails, hsConPatArgs,
HsRecFields(..), HsRecField'(..), LHsRecField',
HsRecField, LHsRecField,
HsRecUpdField, LHsRecUpdField,
hsRecFields, hsRecFieldSel, hsRecFieldId, hsRecFieldsArgs,
hsRecUpdFieldId, hsRecUpdFieldOcc, hsRecUpdFieldRdr,
mkPrefixConPat, mkCharLitPat, mkNilPat,
looksLazyPatBind,
isBangedLPat, isBangedPatBind,
hsPatNeedsParens,
isIrrefutableHsPat,
collectEvVarsPats,
pprParendLPat, pprConArgs
) where
import {-# SOURCE #-} HsExpr (SyntaxExpr, LHsExpr, HsSplice, pprLExpr, pprSplice)
-- friends:
import HsBinds
import HsLit
import PlaceHolder
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 id = LPat id -- No 'Out' constructors
type OutPat id = LPat id -- No 'In' constructors
type LPat id = Located (Pat id)
-- | Pattern
--
-- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnBang'
-- For details on above see note [Api annotations] in ApiAnnotation
data Pat id
= ------------ Simple patterns ---------------
WildPat (PostTc id Type) -- ^ Wildcard Pattern
-- The sole reason for a type on a WildPat is to
-- support hsPatType :: Pat Id -> Type
| VarPat (Located id) -- ^ Variable Pattern
-- See Note [Located RdrNames] in HsExpr
| LazyPat (LPat id) -- ^ Lazy Pattern
-- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnTilde'
-- For details on above see note [Api annotations] in ApiAnnotation
| AsPat (Located id) (LPat id) -- ^ As pattern
-- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnAt'
-- For details on above see note [Api annotations] in ApiAnnotation
| ParPat (LPat id) -- ^ 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 (LPat id) -- ^ Bang pattern
-- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnBang'
-- For details on above see note [Api annotations] in ApiAnnotation
------------ Lists, tuples, arrays ---------------
| ListPat [LPat id]
(PostTc id Type) -- The type of the elements
(Maybe (PostTc id Type, SyntaxExpr id)) -- For rebindable syntax
-- 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 [LPat id] -- Tuple sub-patterns
Boxity -- UnitPat is TuplePat []
[PostTc id Type] -- [] before typechecker, filled in afterwards
-- with the types of the tuple components
-- You might think that the PostTc id 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 (LPat id) -- Sum sub-pattern
ConTag -- Alternative (one-based)
Arity -- Arity
(PostTc id [Type]) -- PlaceHolder before typechecker, filled in
-- afterwards with the types of the
-- alternative
-- ^ Anonymous sum pattern
--
-- - 'ApiAnnotation.AnnKeywordId' :
-- 'ApiAnnotation.AnnOpen' @'(#'@,
-- 'ApiAnnotation.AnnClose' @'#)'@
-- For details on above see note [Api annotations] in ApiAnnotation
| PArrPat [LPat id] -- Syntactic parallel array
(PostTc id Type) -- The type of the elements
-- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'[:'@,
-- 'ApiAnnotation.AnnClose' @':]'@
-- For details on above see note [Api annotations] in ApiAnnotation
------------ Constructor patterns ---------------
| ConPatIn (Located id)
(HsConPatDetails id)
-- ^ 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 id,
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 (LHsExpr id)
(LPat id)
(PostTc id Type) -- The overall type of the pattern
-- (= the argument type of the view function)
-- for hsPatType.
-- ^ View Pattern
------------ Pattern splices ---------------
-- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'$('@
-- 'ApiAnnotation.AnnClose' @')'@
-- For details on above see note [Api annotations] in ApiAnnotation
| SplicePat (HsSplice id) -- ^ Splice Pattern (Includes quasi-quotes)
------------ Literal and n+k patterns ---------------
| LitPat HsLit -- ^ 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
(Located (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
(PostTc id Type) -- Overall type of pattern. Might be
-- different than the literal's type
-- if (==) or negate changes the type
-- ^ Natural Pattern
--
-- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnVal' @'+'@
-- For details on above see note [Api annotations] in ApiAnnotation
| NPlusKPat (Located id) -- n+k pattern
(Located (HsOverLit id)) -- It'll always be an HsIntegral
(HsOverLit id) -- See Note [NPlusK patterns] in TcPat
-- NB: This could be (PostTc ...), but that induced a
-- a new hs-boot file. Not worth it.
(SyntaxExpr id) -- (>=) function, of type t1->t2->Bool
(SyntaxExpr id) -- Name of '-' (see RnEnv.lookupSyntaxName)
(PostTc id Type) -- Type of overall pattern
-- ^ n+k pattern
------------ Pattern type signatures ---------------
-- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDcolon'
-- For details on above see note [Api annotations] in ApiAnnotation
| SigPatIn (LPat id) -- Pattern with a type signature
(LHsSigWcType id) -- Signature can bind both
-- kind and type vars
-- ^ Pattern with a type signature
| SigPatOut (LPat id)
Type
-- ^ Pattern with a type signature
------------ Pattern coercions (translation only) ---------------
| CoPat HsWrapper -- Coercion Pattern
-- 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'
-- ^ Coercion Pattern
deriving instance (DataId id) => Data (Pat id)
-- | Haskell Constructor Pattern Details
type HsConPatDetails id = HsConDetails (LPat id) (HsRecFields id (LPat id))
hsConPatArgs :: HsConPatDetails id -> [LPat id]
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 id arg -- A bunch of record fields
-- { x = 3, y = True }
-- Used for both expressions and patterns
= HsRecFields { rec_flds :: [LHsRecField id arg],
rec_dotdot :: Maybe Int } -- Note [DotDot fields]
deriving (Functor, Foldable, Traversable)
deriving instance (DataId id, Data arg) => Data (HsRecFields id arg)
-- 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' id arg = Located (HsRecField' id arg)
-- | Located Haskell Record Field
type LHsRecField id arg = Located (HsRecField id arg)
-- | Located Haskell Record Update Field
type LHsRecUpdField id = Located (HsRecUpdField id)
-- | Haskell Record Field
type HsRecField id arg = HsRecField' (FieldOcc id) arg
-- | Haskell Record Update Field
type HsRecUpdField id = HsRecField' (AmbiguousFieldOcc id) (LHsExpr id)
-- | 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" PlaceHolder :: AmbiguousFieldOcc RdrName
--
-- After the renamer, this will become:
--
-- hsRecFieldLbl = Ambiguous "x" PlaceHolder :: 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 id arg -> [PostRn id id]
hsRecFields rbinds = map (unLoc . hsRecFieldSel . unLoc) (rec_flds rbinds)
-- Probably won't typecheck at once, things have changed :/
hsRecFieldsArgs :: HsRecFields id arg -> [arg]
hsRecFieldsArgs rbinds = map (hsRecFieldArg . unLoc) (rec_flds rbinds)
hsRecFieldSel :: HsRecField name arg -> Located (PostRn name name)
hsRecFieldSel = fmap selectorFieldOcc . hsRecFieldLbl
hsRecFieldId :: HsRecField Id arg -> Located Id
hsRecFieldId = hsRecFieldSel
hsRecUpdFieldRdr :: HsRecUpdField id -> Located RdrName
hsRecUpdFieldRdr = fmap rdrNameAmbiguousFieldOcc . hsRecFieldLbl
hsRecUpdFieldId :: HsRecField' (AmbiguousFieldOcc Id) arg -> Located Id
hsRecUpdFieldId = fmap selectorFieldOcc . hsRecUpdFieldOcc
hsRecUpdFieldOcc :: HsRecField' (AmbiguousFieldOcc Id) arg -> LFieldOcc Id
hsRecUpdFieldOcc = fmap unambiguousFieldOcc . hsRecFieldLbl
{-
************************************************************************
* *
* Printing patterns
* *
************************************************************************
-}
instance (OutputableBndrId 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
pprPrefixOcc var
pprParendLPat :: (OutputableBndrId name) => LPat name -> SDoc
pprParendLPat (L _ p) = pprParendPat p
pprParendPat :: (OutputableBndrId name) => Pat name -> SDoc
pprParendPat p = sdocWithDynFlags $ \ dflags ->
if need_parens dflags p
then parens (pprPat p)
else pprPat p
where
need_parens dflags p
| CoPat {} <- p = gopt Opt_PrintTypecheckerElaboration dflags
| otherwise = hsPatNeedsParens p
-- 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 name) => Pat name -> SDoc
pprPat (VarPat (L _ var)) = pprPatBndr var
pprPat (WildPat _) = char '_'
pprPat (LazyPat pat) = char '~' <> pprParendLPat pat
pprPat (BangPat pat) = char '!' <> pprParendLPat pat
pprPat (AsPat name pat) = hcat [pprPrefixOcc (unLoc name), char '@', pprParendLPat 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 pat
else pprPat pat)
pprPat (SigPatIn pat ty) = ppr pat <+> dcolon <+> ppr ty
pprPat (SigPatOut pat ty) = ppr pat <+> dcolon <+> ppr ty
pprPat (ListPat pats _ _) = brackets (interpp'SP pats)
pprPat (PArrPat pats _) = paBrackets (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
pprUserCon :: (OutputableBndr con, OutputableBndrId id)
=> con -> HsConPatDetails id -> SDoc
pprUserCon c (InfixCon p1 p2) = ppr p1 <+> pprInfixOcc c <+> ppr p2
pprUserCon c details = pprPrefixOcc c <+> pprConArgs details
pprConArgs :: (OutputableBndrId 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 (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 = text ".." <+> ifPprDebug (ppr (drop n flds))
instance (Outputable id, Outputable arg)
=> Outputable (HsRecField' id arg) where
ppr (HsRecField { hsRecFieldLbl = f, hsRecFieldArg = arg,
hsRecPun = pun })
= ppr f <+> (ppUnless pun $ equals <+> ppr arg)
{-
************************************************************************
* *
* Building patterns
* *
************************************************************************
-}
mkPrefixConPat :: DataCon -> [OutPat id] -> [Type] -> OutPat id
-- 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 id
mkNilPat ty = mkPrefixConPat nilDataCon [] [ty]
mkCharLitPat :: SourceText -> Char -> OutPat id
mkCharLitPat src c = mkPrefixConPat charDataCon
[noLoc $ LitPat (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.
-}
isBangedPatBind :: HsBind id -> Bool
isBangedPatBind (PatBind {pat_lhs = pat}) = isBangedLPat pat
isBangedPatBind _ = False
isBangedLPat :: LPat id -> Bool
isBangedLPat (L _ (ParPat p)) = isBangedLPat p
isBangedLPat (L _ (BangPat {})) = True
isBangedLPat _ = False
looksLazyPatBind :: HsBind id -> 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 (AbsBindsSig { abs_sig_bind = L _ bind })
= looksLazyPatBind bind
looksLazyPatBind _
= False
looksLazyLPat :: LPat id -> Bool
looksLazyLPat (L _ (ParPat p)) = looksLazyLPat p
looksLazyLPat (L _ (AsPat _ p)) = looksLazyLPat p
looksLazyLPat (L _ (BangPat {})) = False
looksLazyLPat (L _ (VarPat {})) = False
looksLazyLPat (L _ (WildPat {})) = False
looksLazyLPat _ = True
isIrrefutableHsPat :: (OutputableBndrId 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.)
--
-- 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 pat
= go pat
where
go (L _ pat) = go1 pat
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 (SumPat _ _ _ _) = False
-- See Note [Unboxed sum patterns aren't irrefutable]
go1 (ListPat {}) = False
go1 (PArrPat {}) = False -- ?
go1 (ConPatIn {}) = False -- Conservative
go1 (ConPatOut{ pat_con = 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 go (hsConPatArgs details)
go1 (ConPatOut{ pat_con = L _ (PatSynCon _pat) })
= False -- Conservative
go1 (LitPat {}) = False
go1 (NPat {}) = False
go1 (NPlusKPat {}) = False
-- We conservatively assume that no TH splices are irrefutable
-- since we cannot know until the splice is evaluated.
go1 (SplicePat {}) = 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!
-}
hsPatNeedsParens :: Pat a -> Bool
hsPatNeedsParens (NPlusKPat {}) = True
hsPatNeedsParens (SplicePat {}) = False
hsPatNeedsParens (ConPatIn _ ds) = conPatNeedsParens ds
hsPatNeedsParens p@(ConPatOut {}) = conPatNeedsParens (pat_args p)
hsPatNeedsParens (SigPatIn {}) = True
hsPatNeedsParens (SigPatOut {}) = True
hsPatNeedsParens (ViewPat {}) = True
hsPatNeedsParens (CoPat _ p _) = hsPatNeedsParens p
hsPatNeedsParens (WildPat {}) = False
hsPatNeedsParens (VarPat {}) = False
hsPatNeedsParens (LazyPat {}) = False
hsPatNeedsParens (BangPat {}) = False
hsPatNeedsParens (ParPat {}) = False
hsPatNeedsParens (AsPat {}) = False
hsPatNeedsParens (TuplePat {}) = False
hsPatNeedsParens (SumPat {}) = False
hsPatNeedsParens (ListPat {}) = False
hsPatNeedsParens (PArrPat {}) = False
hsPatNeedsParens (LitPat {}) = False
hsPatNeedsParens (NPat {}) = False
conPatNeedsParens :: HsConDetails a b -> Bool
conPatNeedsParens (PrefixCon {}) = False
conPatNeedsParens (InfixCon {}) = True
conPatNeedsParens (RecCon {}) = False
{-
% Collect all EvVars from all constructor patterns
-}
-- May need to add more cases
collectEvVarsPats :: [Pat id] -> Bag EvVar
collectEvVarsPats = unionManyBags . map collectEvVarsPat
collectEvVarsLPat :: LPat id -> Bag EvVar
collectEvVarsLPat (L _ pat) = collectEvVarsPat pat
collectEvVarsPat :: Pat id -> 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
PArrPat ps _ -> unionManyBags $ map collectEvVarsLPat ps
ConPatOut {pat_dicts = dicts, pat_args = args}
-> unionBags (listToBag dicts)
$ unionManyBags
$ map collectEvVarsLPat
$ hsConPatArgs args
SigPatOut p _ -> collectEvVarsLPat p
CoPat _ p _ -> collectEvVarsPat p
ConPatIn _ _ -> panic "foldMapPatBag: ConPatIn"
SigPatIn _ _ -> panic "foldMapPatBag: SigPatIn"
_other_pat -> emptyBag