HsPat.hs 24.7 KB
Newer Older
Austin Seipp's avatar
Austin Seipp committed
1 2 3 4
{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

5
\section[PatSyntax]{Abstract Haskell syntax---patterns}
Austin Seipp's avatar
Austin Seipp committed
6
-}
7

8
{-# LANGUAGE DeriveDataTypeable #-}
9 10 11 12 13 14
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE UndecidableInstances #-} -- Note [Pass sensitive types]
                                      -- in module PlaceHolder
{-# LANGUAGE ConstraintKinds #-}
Adam Gundry's avatar
Adam Gundry committed
15
{-# LANGUAGE TypeFamilies #-}
16

17
module HsPat (
Ian Lynagh's avatar
Ian Lynagh committed
18
        Pat(..), InPat, OutPat, LPat,
19

Ian Lynagh's avatar
Ian Lynagh committed
20 21
        HsConDetails(..),
        HsConPatDetails, hsConPatArgs,
Adam Gundry's avatar
Adam Gundry committed
22 23 24 25 26
        HsRecFields(..), HsRecField'(..), LHsRecField',
        HsRecField, LHsRecField,
        HsRecUpdField, LHsRecUpdField,
        hsRecFields, hsRecFieldSel, hsRecFieldId,
        hsRecUpdFieldId, hsRecUpdFieldOcc, hsRecUpdFieldRdr,
Ian Lynagh's avatar
Ian Lynagh committed
27 28

        mkPrefixConPat, mkCharLitPat, mkNilPat,
29

30 31 32
        isUnliftedHsBind, looksLazyPatBind,
        isUnliftedLPat, isBangedLPat, isBangedPatBind,
        hsPatNeedsParens,
33
        isIrrefutableHsPat,
34

35
        pprParendLPat, pprConArgs
36 37
    ) where

38
import {-# SOURCE #-} HsExpr            (SyntaxExpr, LHsExpr, HsSplice, pprLExpr, pprSplice)
sof's avatar
sof committed
39

40
-- friends:
41 42
import HsBinds
import HsLit
Adam Gundry's avatar
Adam Gundry committed
43
import PlaceHolder -- ( PostRn,PostTc,DataId )
44
import HsTypes
45
import TcEvidence
46
import BasicTypes
47
-- others:
Ian Lynagh's avatar
Ian Lynagh committed
48
import PprCore          ( {- instance OutputableBndr TyVar -} )
49 50
import TysWiredIn
import Var
Adam Gundry's avatar
Adam Gundry committed
51
import RdrName ( RdrName )
Gergő Érdi's avatar
Gergő Érdi committed
52
import ConLike
53 54
import DataCon
import TyCon
Ian Lynagh's avatar
Ian Lynagh committed
55
import Outputable
56 57
import Type
import SrcLoc
58
import FastString
Adam Gundry's avatar
Adam Gundry committed
59
import Maybes
60
-- libraries:
61
import Data.Data hiding (TyCon,Fixity)
62

Ian Lynagh's avatar
Ian Lynagh committed
63 64
type InPat id  = LPat id        -- No 'Out' constructors
type OutPat id = LPat id        -- No 'In' constructors
65 66

type LPat id = Located (Pat id)
67

Alan Zimmerman's avatar
Alan Zimmerman committed
68
-- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnBang'
69 70

-- For details on above see note [Api annotations] in ApiAnnotation
71
data Pat id
Ian Lynagh's avatar
Ian Lynagh committed
72
  =     ------------ Simple patterns ---------------
73
    WildPat     (PostTc id Type)        -- Wild card
Ian Lynagh's avatar
Ian Lynagh committed
74 75
        -- The sole reason for a type on a WildPat is to
        -- support hsPatType :: Pat Id -> Type
76

77
  | VarPat      (Located id)            -- Variable
78
  | LazyPat     (LPat id)               -- Lazy pattern
Alan Zimmerman's avatar
Alan Zimmerman committed
79 80
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnTilde'

81 82
    -- For details on above see note [Api annotations] in ApiAnnotation

Ian Lynagh's avatar
Ian Lynagh committed
83
  | AsPat       (Located id) (LPat id)  -- As pattern
Alan Zimmerman's avatar
Alan Zimmerman committed
84 85
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnAt'

86 87
    -- For details on above see note [Api annotations] in ApiAnnotation

Ian Lynagh's avatar
Ian Lynagh committed
88 89
  | ParPat      (LPat id)               -- Parenthesised pattern
                                        -- See Note [Parens in HsSyn] in HsExpr
Alan Zimmerman's avatar
Alan Zimmerman committed
90 91
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'('@,
    --                                    'ApiAnnotation.AnnClose' @')'@
92 93

    -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
94
  | BangPat     (LPat id)               -- Bang pattern
Alan Zimmerman's avatar
Alan Zimmerman committed
95
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnBang'
Ian Lynagh's avatar
Ian Lynagh committed
96

97 98
    -- For details on above see note [Api annotations] in ApiAnnotation

Ian Lynagh's avatar
Ian Lynagh committed
99
        ------------ Lists, tuples, arrays ---------------
100
  | ListPat     [LPat id]                            -- Syntactic list
101 102
                (PostTc id Type)                     -- The type of the elements
                (Maybe (PostTc id Type, SyntaxExpr id)) -- For rebindable syntax
103 104 105
                   -- For OverloadedLists a Just (ty,fn) gives
                   -- overall type of the pattern, and the toList
                   -- function to convert the scrutinee to a list value
Alan Zimmerman's avatar
Alan Zimmerman committed
106 107
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'['@,
    --                                    'ApiAnnotation.AnnClose' @']'@
Ian Lynagh's avatar
Ian Lynagh committed
108

109 110
    -- For details on above see note [Api annotations] in ApiAnnotation

111 112 113 114 115
  | 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
116 117
        -- get the pattern type by getting the types of the sub-patterns.
        -- But it's essential
Ian Lynagh's avatar
Ian Lynagh committed
118 119 120 121 122 123 124 125 126 127
        --      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
128 129
        -- (June 14: I'm not sure this comment is right; the sub-patterns
        --           will be wrapped in CoPats, no?)
Alan Zimmerman's avatar
Alan Zimmerman committed
130 131 132
    -- ^ - 'ApiAnnotation.AnnKeywordId' :
    --            'ApiAnnotation.AnnOpen' @'('@ or @'(#'@,
    --            'ApiAnnotation.AnnClose' @')'@ or  @'#)'@
Ian Lynagh's avatar
Ian Lynagh committed
133

134
    -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
135
  | PArrPat     [LPat id]               -- Syntactic parallel array
136
                (PostTc id Type)        -- The type of the elements
Alan Zimmerman's avatar
Alan Zimmerman committed
137 138
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'[:'@,
    --                                    'ApiAnnotation.AnnClose' @':]'@
Ian Lynagh's avatar
Ian Lynagh committed
139

140
    -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
141 142 143
        ------------ Constructor patterns ---------------
  | ConPatIn    (Located id)
                (HsConPatDetails id)
144

145
  | ConPatOut {
146
        pat_con     :: Located ConLike,
Gabor Greif's avatar
Gabor Greif committed
147
        pat_arg_tys :: [Type],          -- The universal arg types, 1-1 with the universal
148
                                        -- tyvars of the constructor/pattern synonym
Austin Seipp's avatar
Austin Seipp committed
149
                                        --   Use (conLikeResTy pat_con pat_arg_tys) to get
150 151
                                        --   the type of the pattern

Ian Lynagh's avatar
Ian Lynagh committed
152 153 154 155 156 157
        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,
Gergő Érdi's avatar
Gergő Érdi committed
158
        pat_wrap  :: HsWrapper          -- Extra wrapper to pass to the matcher
159
    }
160

Ian Lynagh's avatar
Ian Lynagh committed
161
        ------------ View patterns ---------------
Alan Zimmerman's avatar
Alan Zimmerman committed
162
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnRarrow'
163 164

  -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
165
  | ViewPat       (LHsExpr id)
166
                  (LPat id)
167
                  (PostTc id Type)  -- The overall type of the pattern
168 169 170
                                    -- (= the argument type of the view function)
                                    -- for hsPatType.

gmainland's avatar
gmainland committed
171
        ------------ Pattern splices ---------------
Alan Zimmerman's avatar
Alan Zimmerman committed
172 173
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'$('@
  --        'ApiAnnotation.AnnClose' @')'@
174 175

  -- For details on above see note [Api annotations] in ApiAnnotation
176
  | SplicePat       (HsSplice id)   -- Includes quasi-quotes
177

Ian Lynagh's avatar
Ian Lynagh committed
178 179 180 181 182 183
        ------------ Literal and n+k patterns ---------------
  | LitPat          HsLit               -- Used for *non-overloaded* literal patterns:
                                        -- Int#, Char#, Int, Char, String, etc.

  | NPat                -- Used for all overloaded literals,
                        -- including overloaded strings with -XOverloadedStrings
Alan Zimmerman's avatar
Alan Zimmerman committed
184
                    (Located (HsOverLit id))    -- ALWAYS positive
Ian Lynagh's avatar
Ian Lynagh committed
185 186 187 188
                    (Maybe (SyntaxExpr id))     -- Just (Name of 'negate') for negative
                                                -- patterns, Nothing otherwise
                    (SyntaxExpr id)             -- Equality checker, of type t->t->Bool

Alan Zimmerman's avatar
Alan Zimmerman committed
189
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnVal' @'+'@
190 191

  -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
192
  | NPlusKPat       (Located id)        -- n+k pattern
Alan Zimmerman's avatar
Alan Zimmerman committed
193
                    (Located (HsOverLit id)) -- It'll always be an HsIntegral
Ian Lynagh's avatar
Ian Lynagh committed
194 195 196 197
                    (SyntaxExpr id)     -- (>=) function, of type t->t->Bool
                    (SyntaxExpr id)     -- Name of '-' (see RnEnv.lookupSyntaxName)

        ------------ Pattern type signatures ---------------
Alan Zimmerman's avatar
Alan Zimmerman committed
198
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDcolon'
199 200

  -- For details on above see note [Api annotations] in ApiAnnotation
201 202 203
  | SigPatIn        (LPat id)                  -- Pattern with a type signature
                    (HsWithBndrs id (LHsType id)) -- Signature can bind both
                                                  -- kind and type vars
Ian Lynagh's avatar
Ian Lynagh committed
204 205 206 207 208 209 210 211 212 213 214

  | 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'
215 216
  deriving (Typeable)
deriving instance (DataId id) => Data (Pat id)
217

Austin Seipp's avatar
Austin Seipp committed
218
-- HsConDetails is use for patterns/expressions *and* for data type declarations
219

220 221
data HsConDetails arg rec
  = PrefixCon [arg]             -- C p1 p2 p3
Ian Lynagh's avatar
Ian Lynagh committed
222 223
  | RecCon    rec               -- C { x = p1, y = p2 }
  | InfixCon  arg arg           -- p1 `C` p2
224
  deriving (Data, Typeable)
225 226 227 228 229

type HsConPatDetails id = HsConDetails (LPat id) (HsRecFields id (LPat id))

hsConPatArgs :: HsConPatDetails id -> [LPat id]
hsConPatArgs (PrefixCon ps)   = ps
230
hsConPatArgs (RecCon fs)      = map (hsRecFieldArg . unLoc) (rec_flds fs)
231 232
hsConPatArgs (InfixCon p1 p2) = [p1,p2]

Austin Seipp's avatar
Austin Seipp committed
233
{-
234 235
However HsRecFields is used only for patterns and expressions
(not data type declarations)
Austin Seipp's avatar
Austin Seipp committed
236
-}
237

Ian Lynagh's avatar
Ian Lynagh committed
238 239 240
data HsRecFields id arg         -- A bunch of record fields
                                --      { x = 3, y = True }
        -- Used for both expressions and patterns
241
  = HsRecFields { rec_flds   :: [LHsRecField id arg],
Ian Lynagh's avatar
Ian Lynagh committed
242
                  rec_dotdot :: Maybe Int }  -- Note [DotDot fields]
Adam Gundry's avatar
Adam Gundry committed
243 244
  deriving (Typeable)
deriving instance (DataId id, Data arg) => Data (HsRecFields id arg)
245 246 247 248 249

-- Note [DotDot fields]
-- ~~~~~~~~~~~~~~~~~~~~
-- The rec_dotdot field means this:
--   Nothing => the normal case
Ian Lynagh's avatar
Ian Lynagh committed
250
--   Just n  => the group uses ".." notation,
251
--
Ian Lynagh's avatar
Ian Lynagh committed
252
-- In the latter case:
253 254 255
--
--   *before* renamer: rec_flds are exactly the n user-written fields
--
Ian Lynagh's avatar
Ian Lynagh committed
256 257 258
--   *after* renamer:  rec_flds includes *all* fields, with
--                     the first 'n' being the user-written ones
--                     and the remainder being 'filled in' implicitly
259

Adam Gundry's avatar
Adam Gundry committed
260 261 262 263 264 265
type LHsRecField' id arg = Located (HsRecField' id arg)
type LHsRecField  id arg = Located (HsRecField  id arg)
type LHsRecUpdField id   = Located (HsRecUpdField id)

type HsRecField    id arg = HsRecField' (FieldOcc id) arg
type HsRecUpdField id     = HsRecField' (AmbiguousFieldOcc id) (LHsExpr id)
266

Adam Gundry's avatar
Adam Gundry committed
267 268
-- |  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnEqual',
--
269
-- For details on above see note [Api annotations] in ApiAnnotation
Adam Gundry's avatar
Adam Gundry committed
270 271 272 273
data HsRecField' id arg = HsRecField {
        hsRecFieldLbl :: Located id,
        hsRecFieldArg :: arg,           -- ^ Filled in by renamer when punning
        hsRecPun      :: Bool           -- ^ Note [Punning]
274
  } deriving (Data, Typeable)
275

Adam Gundry's avatar
Adam Gundry committed
276

277 278 279
-- Note [Punning]
-- ~~~~~~~~~~~~~~
-- If you write T { x, y = v+1 }, the HsRecFields will be
Ian Lynagh's avatar
Ian Lynagh committed
280 281 282
--      HsRecField x x True ...
--      HsRecField y (v+1) False ...
-- That is, for "punned" field x is expanded (in the renamer)
283
-- to x=x; but with a punning flag so we can detect it later
284
-- (e.g. when pretty printing)
285 286 287
--
-- If the original field was qualified, we un-qualify it, thus
--    T { A.x } means T { A.x = x }
288

Adam Gundry's avatar
Adam Gundry committed
289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327

-- 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
328 329
--
-- See also Note [Disambiguating record fields] in TcExpr.
Adam Gundry's avatar
Adam Gundry committed
330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348

hsRecFields :: HsRecFields id arg -> [PostRn id id]
hsRecFields rbinds = map (unLoc . hsRecFieldSel . 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

349

Austin Seipp's avatar
Austin Seipp committed
350 351 352 353 354 355 356
{-
************************************************************************
*                                                                      *
*              Printing patterns
*                                                                      *
************************************************************************
-}
357

358 359 360
instance (OutputableBndr name) => Outputable (Pat name) where
    ppr = pprPat

361
pprPatBndr :: OutputableBndr name => name -> SDoc
Ian Lynagh's avatar
Ian Lynagh committed
362
pprPatBndr var                  -- Print with type info if -dppr-debug is on
363 364
  = getPprStyle $ \ sty ->
    if debugStyle sty then
Ian Lynagh's avatar
Ian Lynagh committed
365 366
        parens (pprBndr LambdaBind var)         -- Could pass the site to pprPat
                                                -- but is it worth it?
367
    else
368
        pprPrefixOcc var
369

370 371 372 373
pprParendLPat :: (OutputableBndr name) => LPat name -> SDoc
pprParendLPat (L _ p) = pprParendPat p

pprParendPat :: (OutputableBndr name) => Pat name -> SDoc
374 375 376 377 378 379 380 381 382 383 384
pprParendPat p = getPprStyle $ \ sty ->
                 if need_parens sty p
                 then parens (pprPat p)
                 else  pprPat p
  where
    need_parens sty p
      | CoPat {} <- p          -- In debug style we print the cast
      , debugStyle sty = True  -- (see pprHsWrapper) so parens are needed
      | otherwise      = hsPatNeedsParens p
                         -- But otherwise the CoPat is discarded, so it
                         -- is the pattern inside that matters.  Sigh.
385

386
pprPat :: (OutputableBndr name) => Pat name -> SDoc
387
pprPat (VarPat (L _ var))     = pprPatBndr var
388 389 390 391 392 393 394 395 396 397 398 399 400 401
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 (ppr pat) co
pprPat (SigPatIn pat ty)      = ppr pat <+> dcolon <+> ppr ty
pprPat (SigPatOut pat ty)     = ppr pat <+> dcolon <+> ppr ty
402
pprPat (ListPat pats _ _)     = brackets (interpp'SP pats)
403 404
pprPat (PArrPat pats _)       = paBrackets (interpp'SP pats)
pprPat (TuplePat pats bx _)   = tupleParens (boxityTupleSort bx) (pprWithCommas ppr pats)
405
pprPat (ConPatIn con details) = pprUserCon (unLoc con) details
Ian Lynagh's avatar
Ian Lynagh committed
406 407 408 409 410
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
Gergő Érdi's avatar
Gergő Érdi committed
411 412 413 414
        ppr con
          <> braces (sep [ hsep (map pprPatBndr (tvs ++ dicts))
                         , ppr binds])
          <+> pprConArgs details
415
    else pprUserCon (unLoc con) details
416 417


418 419 420
pprUserCon :: (OutputableBndr con, OutputableBndr id) => con -> HsConPatDetails id -> SDoc
pprUserCon c (InfixCon p1 p2) = ppr p1 <+> pprInfixOcc c <+> ppr p2
pprUserCon c details          = pprPrefixOcc c <+> pprConArgs details
421

422
pprConArgs ::  OutputableBndr id => HsConPatDetails id -> SDoc
423 424
pprConArgs (PrefixCon pats) = sep (map pprParendLPat pats)
pprConArgs (InfixCon p1 p2) = sep [pprParendLPat p1, pprParendLPat p2]
425 426
pprConArgs (RecCon rpats)   = ppr rpats

Adam Gundry's avatar
Adam Gundry committed
427
instance (Outputable arg)
428 429
      => Outputable (HsRecFields id arg) where
  ppr (HsRecFields { rec_flds = flds, rec_dotdot = Nothing })
Ian Lynagh's avatar
Ian Lynagh committed
430
        = braces (fsep (punctuate comma (map ppr flds)))
431
  ppr (HsRecFields { rec_flds = flds, rec_dotdot = Just n })
Ian Lynagh's avatar
Ian Lynagh committed
432 433 434
        = braces (fsep (punctuate comma (map ppr (take n flds) ++ [dotdot])))
        where
          dotdot = ptext (sLit "..") <+> ifPprDebug (ppr (drop n flds))
435

Adam Gundry's avatar
Adam Gundry committed
436 437 438
instance (Outputable id, Outputable arg)
      => Outputable (HsRecField' id arg) where
  ppr (HsRecField { hsRecFieldLbl = f, hsRecFieldArg = arg,
Ian Lynagh's avatar
Ian Lynagh committed
439
                    hsRecPun = pun })
440
    = ppr f <+> (ppUnless pun $ equals <+> ppr arg)
441

Adam Gundry's avatar
Adam Gundry committed
442

Austin Seipp's avatar
Austin Seipp committed
443 444 445 446 447 448 449
{-
************************************************************************
*                                                                      *
*              Building patterns
*                                                                      *
************************************************************************
-}
450

451
mkPrefixConPat :: DataCon -> [OutPat id] -> [Type] -> OutPat id
452
-- Make a vanilla Prefix constructor pattern
453
mkPrefixConPat dc pats tys
Gergő Érdi's avatar
Gergő Érdi committed
454
  = noLoc $ ConPatOut { pat_con = noLoc (RealDataCon dc), pat_tvs = [], pat_dicts = [],
Ian Lynagh's avatar
Ian Lynagh committed
455
                        pat_binds = emptyTcEvBinds, pat_args = PrefixCon pats,
456
                        pat_arg_tys = tys, pat_wrap = idHsWrapper }
457

458
mkNilPat :: Type -> OutPat id
459
mkNilPat ty = mkPrefixConPat nilDataCon [] [ty]
460

461 462 463
mkCharLitPat :: String -> Char -> OutPat id
mkCharLitPat src c = mkPrefixConPat charDataCon
                                    [noLoc $ LitPat (HsCharPrim src c)] []
464

Austin Seipp's avatar
Austin Seipp committed
465 466 467 468 469 470
{-
************************************************************************
*                                                                      *
* Predicates for checking things about pattern-lists in EquationInfo   *
*                                                                      *
************************************************************************
471

472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493
\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.

494
The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
Austin Seipp's avatar
Austin Seipp committed
495 496
-}

497 498 499 500
isUnliftedLPat :: LPat id -> Bool
isUnliftedLPat (L _ (ParPat p))             = isUnliftedLPat p
isUnliftedLPat (L _ (TuplePat _ Unboxed _)) = True
isUnliftedLPat _                            = False
501

502
isUnliftedHsBind :: HsBind id -> Bool
503
-- A pattern binding with an outermost bang or unboxed tuple must be matched strictly
504
-- Defined in this module because HsPat is above HsBinds in the import graph
505 506 507 508 509 510 511 512 513 514 515
isUnliftedHsBind (PatBind { pat_lhs = p }) = isUnliftedLPat p
isUnliftedHsBind _                         = False

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
516 517 518

looksLazyPatBind :: HsBind id -> Bool
-- Returns True of anything *except*
Austin Seipp's avatar
Austin Seipp committed
519
--     a StrictHsBind (as above) or
520 521 522 523 524 525 526 527 528 529 530 531 532
--     a VarPat
-- In particular, returns True of a pattern binding with a compound pattern, like (I# x)
looksLazyPatBind (PatBind { pat_lhs = p }) = looksLazyLPat p
looksLazyPatBind _                         = False

looksLazyLPat :: LPat id -> Bool
looksLazyLPat (L _ (ParPat p))             = looksLazyLPat p
looksLazyLPat (L _ (AsPat _ p))            = looksLazyLPat p
looksLazyLPat (L _ (BangPat {}))           = False
looksLazyLPat (L _ (TuplePat _ Unboxed _)) = False
looksLazyLPat (L _ (VarPat {}))            = False
looksLazyLPat (L _ (WildPat {}))           = False
looksLazyLPat _                            = True
533

534
isIrrefutableHsPat :: OutputableBndr id => LPat id -> Bool
535 536
-- (isIrrefutableHsPat p) is true if matching against p cannot fail,
-- in the sense of falling through to the next pattern.
Ian Lynagh's avatar
Ian Lynagh committed
537 538 539
--      (NB: this is not quite the same as the (silly) defn
--      in 3.17.2 of the Haskell 98 report.)
--
540
-- isIrrefutableHsPat returns False if it's in doubt; specifically
541
-- on a ConPatIn it doesn't know the size of the constructor family
542 543 544 545
-- But if it returns True, the pattern is definitely irrefutable
isIrrefutableHsPat pat
  = go pat
  where
546
    go (L _ pat) = go1 pat
547

548 549 550
    go1 (WildPat {})        = True
    go1 (VarPat {})         = True
    go1 (LazyPat {})        = True
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
551
    go1 (BangPat pat)       = go pat
552
    go1 (CoPat _ pat _)     = go1 pat
553 554
    go1 (ParPat pat)        = go pat
    go1 (AsPat _ pat)       = go pat
555
    go1 (ViewPat _ pat _)   = go pat
556 557 558
    go1 (SigPatIn pat _)    = go pat
    go1 (SigPatOut pat _)   = go pat
    go1 (TuplePat pats _ _) = all go pats
559
    go1 (ListPat {}) = False
Ian Lynagh's avatar
Ian Lynagh committed
560
    go1 (PArrPat {})        = False     -- ?
561

Ian Lynagh's avatar
Ian Lynagh committed
562
    go1 (ConPatIn {})       = False     -- Conservative
Gergő Érdi's avatar
Gergő Érdi committed
563
    go1 (ConPatOut{ pat_con = L _ (RealDataCon con), pat_args = details })
Ian Lynagh's avatar
Ian Lynagh committed
564 565 566 567
        =  isJust (tyConSingleDataCon_maybe (dataConTyCon con))
           -- NB: tyConSingleDataCon_maybe, *not* isProductTyCon, because
           -- the latter is false of existentials. See Trac #4439
        && all go (hsConPatArgs details)
Gergő Érdi's avatar
Gergő Érdi committed
568 569
    go1 (ConPatOut{ pat_con = L _ (PatSynCon _pat) })
        = False -- Conservative
570

571 572 573
    go1 (LitPat {})    = False
    go1 (NPat {})      = False
    go1 (NPlusKPat {}) = False
574

gmainland's avatar
gmainland committed
575 576
    -- Both should be gotten rid of by renamer before
    -- isIrrefutablePat is called
Austin Seipp's avatar
Austin Seipp committed
577
    go1 (SplicePat {})     = urk pat
578 579

    urk pat = pprPanic "isIrrefutableHsPat:" (ppr pat)
580 581

hsPatNeedsParens :: Pat a -> Bool
582
hsPatNeedsParens (NPlusKPat {})      = True
gmainland's avatar
gmainland committed
583
hsPatNeedsParens (SplicePat {})      = False
584 585 586 587 588
hsPatNeedsParens (ConPatIn _ ds)     = conPatNeedsParens ds
hsPatNeedsParens p@(ConPatOut {})    = conPatNeedsParens (pat_args p)
hsPatNeedsParens (SigPatIn {})       = True
hsPatNeedsParens (SigPatOut {})      = True
hsPatNeedsParens (ViewPat {})        = True
589
hsPatNeedsParens (CoPat _ p _)       = hsPatNeedsParens p
590 591 592 593 594 595 596 597
hsPatNeedsParens (WildPat {})        = False
hsPatNeedsParens (VarPat {})         = False
hsPatNeedsParens (LazyPat {})        = False
hsPatNeedsParens (BangPat {})        = False
hsPatNeedsParens (ParPat {})         = False
hsPatNeedsParens (AsPat {})          = False
hsPatNeedsParens (TuplePat {})       = False
hsPatNeedsParens (ListPat {})        = False
Ian Lynagh's avatar
Ian Lynagh committed
598 599 600
hsPatNeedsParens (PArrPat {})        = False
hsPatNeedsParens (LitPat {})         = False
hsPatNeedsParens (NPat {})           = False
601 602 603

conPatNeedsParens :: HsConDetails a b -> Bool
conPatNeedsParens (PrefixCon args) = not (null args)
604 605
conPatNeedsParens (InfixCon {})    = True
conPatNeedsParens (RecCon {})      = True