HsPat.hs 21.8 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 #-}
15

16
module HsPat (
Ian Lynagh's avatar
Ian Lynagh committed
17
        Pat(..), InPat, OutPat, LPat,
18

Ian Lynagh's avatar
Ian Lynagh committed
19 20
        HsConDetails(..),
        HsConPatDetails, hsConPatArgs,
21
        HsRecFields(..), HsRecField(..), LHsRecField, hsRecFields,
Ian Lynagh's avatar
Ian Lynagh committed
22 23

        mkPrefixConPat, mkCharLitPat, mkNilPat,
24

25 26
        isStrictHsBind, looksLazyPatBind,
        isStrictLPat, hsPatNeedsParens,
27
        isIrrefutableHsPat,
28

29
        pprParendLPat, pprConArgs
30 31
    ) where

32
import {-# SOURCE #-} HsExpr            (SyntaxExpr, LHsExpr, HsSplice, pprLExpr, pprSplice)
sof's avatar
sof committed
33

34
-- friends:
35 36
import HsBinds
import HsLit
37
import PlaceHolder ( PostTc,DataId )
38
import HsTypes
39
import TcEvidence
40
import BasicTypes
41
-- others:
Ian Lynagh's avatar
Ian Lynagh committed
42
import PprCore          ( {- instance OutputableBndr TyVar -} )
43 44
import TysWiredIn
import Var
Gergő Érdi's avatar
Gergő Érdi committed
45
import ConLike
46 47
import DataCon
import TyCon
Ian Lynagh's avatar
Ian Lynagh committed
48
import Outputable
49 50
import Type
import SrcLoc
51
import FastString
52
-- libraries:
53
import Data.Data hiding (TyCon,Fixity)
54
import Data.Maybe
55

Ian Lynagh's avatar
Ian Lynagh committed
56 57
type InPat id  = LPat id        -- No 'Out' constructors
type OutPat id = LPat id        -- No 'In' constructors
58 59

type LPat id = Located (Pat id)
60

Alan Zimmerman's avatar
Alan Zimmerman committed
61
-- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnBang'
62 63

-- For details on above see note [Api annotations] in ApiAnnotation
64
data Pat id
Ian Lynagh's avatar
Ian Lynagh committed
65
  =     ------------ Simple patterns ---------------
66
    WildPat     (PostTc id Type)        -- Wild card
Ian Lynagh's avatar
Ian Lynagh committed
67 68
        -- The sole reason for a type on a WildPat is to
        -- support hsPatType :: Pat Id -> Type
69

Ian Lynagh's avatar
Ian Lynagh committed
70
  | VarPat      id                      -- Variable
71
  | LazyPat     (LPat id)               -- Lazy pattern
Alan Zimmerman's avatar
Alan Zimmerman committed
72 73
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnTilde'

74 75
    -- For details on above see note [Api annotations] in ApiAnnotation

Ian Lynagh's avatar
Ian Lynagh committed
76
  | AsPat       (Located id) (LPat id)  -- As pattern
Alan Zimmerman's avatar
Alan Zimmerman committed
77 78
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnAt'

79 80
    -- For details on above see note [Api annotations] in ApiAnnotation

Ian Lynagh's avatar
Ian Lynagh committed
81 82
  | ParPat      (LPat id)               -- Parenthesised pattern
                                        -- See Note [Parens in HsSyn] in HsExpr
Alan Zimmerman's avatar
Alan Zimmerman committed
83 84
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'('@,
    --                                    'ApiAnnotation.AnnClose' @')'@
85 86

    -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
87
  | BangPat     (LPat id)               -- Bang pattern
Alan Zimmerman's avatar
Alan Zimmerman committed
88
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnBang'
Ian Lynagh's avatar
Ian Lynagh committed
89

90 91
    -- For details on above see note [Api annotations] in ApiAnnotation

Ian Lynagh's avatar
Ian Lynagh committed
92
        ------------ Lists, tuples, arrays ---------------
93
  | ListPat     [LPat id]                            -- Syntactic list
94 95
                (PostTc id Type)                     -- The type of the elements
                (Maybe (PostTc id Type, SyntaxExpr id)) -- For rebindable syntax
96 97 98
                   -- 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
99 100
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'['@,
    --                                    'ApiAnnotation.AnnClose' @']'@
Ian Lynagh's avatar
Ian Lynagh committed
101

102 103
    -- For details on above see note [Api annotations] in ApiAnnotation

104 105 106 107 108
  | 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
109 110
        -- get the pattern type by getting the types of the sub-patterns.
        -- But it's essential
Ian Lynagh's avatar
Ian Lynagh committed
111 112 113 114 115 116 117 118 119 120
        --      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
121 122
        -- (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
123 124 125
    -- ^ - 'ApiAnnotation.AnnKeywordId' :
    --            'ApiAnnotation.AnnOpen' @'('@ or @'(#'@,
    --            'ApiAnnotation.AnnClose' @')'@ or  @'#)'@
Ian Lynagh's avatar
Ian Lynagh committed
126

127
    -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
128
  | PArrPat     [LPat id]               -- Syntactic parallel array
129
                (PostTc id Type)        -- The type of the elements
Alan Zimmerman's avatar
Alan Zimmerman committed
130 131
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'[:'@,
    --                                    'ApiAnnotation.AnnClose' @':]'@
Ian Lynagh's avatar
Ian Lynagh committed
132

133
    -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
134 135 136
        ------------ Constructor patterns ---------------
  | ConPatIn    (Located id)
                (HsConPatDetails id)
137

138
  | ConPatOut {
139
        pat_con     :: Located ConLike,
Gabor Greif's avatar
Gabor Greif committed
140
        pat_arg_tys :: [Type],          -- The universal arg types, 1-1 with the universal
141
                                        -- tyvars of the constructor/pattern synonym
Austin Seipp's avatar
Austin Seipp committed
142
                                        --   Use (conLikeResTy pat_con pat_arg_tys) to get
143 144
                                        --   the type of the pattern

Ian Lynagh's avatar
Ian Lynagh committed
145 146 147 148 149 150
        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
151
        pat_wrap  :: HsWrapper          -- Extra wrapper to pass to the matcher
152
    }
153

Ian Lynagh's avatar
Ian Lynagh committed
154
        ------------ View patterns ---------------
Alan Zimmerman's avatar
Alan Zimmerman committed
155
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnRarrow'
156 157

  -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
158
  | ViewPat       (LHsExpr id)
159
                  (LPat id)
160
                  (PostTc id Type)  -- The overall type of the pattern
161 162 163
                                    -- (= the argument type of the view function)
                                    -- for hsPatType.

gmainland's avatar
gmainland committed
164
        ------------ Pattern splices ---------------
Alan Zimmerman's avatar
Alan Zimmerman committed
165 166
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'$('@
  --        'ApiAnnotation.AnnClose' @')'@
167 168

  -- For details on above see note [Api annotations] in ApiAnnotation
169
  | SplicePat       (HsSplice id)   -- Includes quasi-quotes
170

Ian Lynagh's avatar
Ian Lynagh committed
171 172 173 174 175 176
        ------------ 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
177
                    (Located (HsOverLit id))    -- ALWAYS positive
Ian Lynagh's avatar
Ian Lynagh committed
178 179 180 181
                    (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
182
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnVal' @'+'@
183 184

  -- For details on above see note [Api annotations] in ApiAnnotation
Ian Lynagh's avatar
Ian Lynagh committed
185
  | NPlusKPat       (Located id)        -- n+k pattern
Alan Zimmerman's avatar
Alan Zimmerman committed
186
                    (Located (HsOverLit id)) -- It'll always be an HsIntegral
Ian Lynagh's avatar
Ian Lynagh committed
187 188 189 190
                    (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
191
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDcolon'
192 193

  -- For details on above see note [Api annotations] in ApiAnnotation
194 195 196
  | 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
197 198 199 200 201 202 203 204 205 206 207

  | 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'
208 209
  deriving (Typeable)
deriving instance (DataId id) => Data (Pat id)
210

Austin Seipp's avatar
Austin Seipp committed
211
-- HsConDetails is use for patterns/expressions *and* for data type declarations
212

213 214
data HsConDetails arg rec
  = PrefixCon [arg]             -- C p1 p2 p3
Ian Lynagh's avatar
Ian Lynagh committed
215 216
  | RecCon    rec               -- C { x = p1, y = p2 }
  | InfixCon  arg arg           -- p1 `C` p2
217
  deriving (Data, Typeable)
218 219 220 221 222

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

hsConPatArgs :: HsConPatDetails id -> [LPat id]
hsConPatArgs (PrefixCon ps)   = ps
223
hsConPatArgs (RecCon fs)      = map (hsRecFieldArg . unLoc) (rec_flds fs)
224 225
hsConPatArgs (InfixCon p1 p2) = [p1,p2]

Austin Seipp's avatar
Austin Seipp committed
226
{-
227 228
However HsRecFields is used only for patterns and expressions
(not data type declarations)
Austin Seipp's avatar
Austin Seipp committed
229
-}
230

Ian Lynagh's avatar
Ian Lynagh committed
231 232 233
data HsRecFields id arg         -- A bunch of record fields
                                --      { x = 3, y = True }
        -- Used for both expressions and patterns
234
  = HsRecFields { rec_flds   :: [LHsRecField id arg],
Ian Lynagh's avatar
Ian Lynagh committed
235
                  rec_dotdot :: Maybe Int }  -- Note [DotDot fields]
236
  deriving (Data, Typeable)
237 238 239 240 241

-- Note [DotDot fields]
-- ~~~~~~~~~~~~~~~~~~~~
-- The rec_dotdot field means this:
--   Nothing => the normal case
Ian Lynagh's avatar
Ian Lynagh committed
242
--   Just n  => the group uses ".." notation,
243
--
Ian Lynagh's avatar
Ian Lynagh committed
244
-- In the latter case:
245 246 247
--
--   *before* renamer: rec_flds are exactly the n user-written fields
--
Ian Lynagh's avatar
Ian Lynagh committed
248 249 250
--   *after* renamer:  rec_flds includes *all* fields, with
--                     the first 'n' being the user-written ones
--                     and the remainder being 'filled in' implicitly
251

252
type LHsRecField id arg = Located (HsRecField id arg)
Alan Zimmerman's avatar
Alan Zimmerman committed
253
-- |  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnEqual',
254 255

-- For details on above see note [Api annotations] in ApiAnnotation
256
data HsRecField id arg = HsRecField {
Ian Lynagh's avatar
Ian Lynagh committed
257 258 259
        hsRecFieldId  :: Located id,
        hsRecFieldArg :: arg,           -- Filled in by renamer
        hsRecPun      :: Bool           -- Note [Punning]
260
  } deriving (Data, Typeable)
261 262 263 264

-- Note [Punning]
-- ~~~~~~~~~~~~~~
-- If you write T { x, y = v+1 }, the HsRecFields will be
Ian Lynagh's avatar
Ian Lynagh committed
265 266 267
--      HsRecField x x True ...
--      HsRecField y (v+1) False ...
-- That is, for "punned" field x is expanded (in the renamer)
268
-- to x=x; but with a punning flag so we can detect it later
269
-- (e.g. when pretty printing)
270 271 272
--
-- If the original field was qualified, we un-qualify it, thus
--    T { A.x } means T { A.x = x }
273 274

hsRecFields :: HsRecFields id arg -> [id]
275
hsRecFields rbinds = map (unLoc . hsRecFieldId . unLoc) (rec_flds rbinds)
276

Austin Seipp's avatar
Austin Seipp committed
277 278 279 280 281 282 283
{-
************************************************************************
*                                                                      *
*              Printing patterns
*                                                                      *
************************************************************************
-}
284

285 286 287
instance (OutputableBndr name) => Outputable (Pat name) where
    ppr = pprPat

288
pprPatBndr :: OutputableBndr name => name -> SDoc
Ian Lynagh's avatar
Ian Lynagh committed
289
pprPatBndr var                  -- Print with type info if -dppr-debug is on
290 291
  = getPprStyle $ \ sty ->
    if debugStyle sty then
Ian Lynagh's avatar
Ian Lynagh committed
292 293
        parens (pprBndr LambdaBind var)         -- Could pass the site to pprPat
                                                -- but is it worth it?
294
    else
295
        pprPrefixOcc var
296

297 298 299 300
pprParendLPat :: (OutputableBndr name) => LPat name -> SDoc
pprParendLPat (L _ p) = pprParendPat p

pprParendPat :: (OutputableBndr name) => Pat name -> SDoc
301 302 303 304 305 306 307 308 309 310 311
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.
312

313
pprPat :: (OutputableBndr name) => Pat name -> SDoc
314 315 316 317 318 319 320 321 322 323 324 325 326 327 328
pprPat (VarPat 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 (ppr pat) co
pprPat (SigPatIn pat ty)      = ppr pat <+> dcolon <+> ppr ty
pprPat (SigPatOut pat ty)     = ppr pat <+> dcolon <+> ppr ty
329
pprPat (ListPat pats _ _)     = brackets (interpp'SP pats)
330 331
pprPat (PArrPat pats _)       = paBrackets (interpp'SP pats)
pprPat (TuplePat pats bx _)   = tupleParens (boxityTupleSort bx) (pprWithCommas ppr pats)
332
pprPat (ConPatIn con details) = pprUserCon (unLoc con) details
Ian Lynagh's avatar
Ian Lynagh committed
333 334 335 336 337
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
338 339 340 341
        ppr con
          <> braces (sep [ hsep (map pprPatBndr (tvs ++ dicts))
                         , ppr binds])
          <+> pprConArgs details
342
    else pprUserCon (unLoc con) details
343 344


345 346 347
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
348

349
pprConArgs ::  OutputableBndr id => HsConPatDetails id -> SDoc
350 351
pprConArgs (PrefixCon pats) = sep (map pprParendLPat pats)
pprConArgs (InfixCon p1 p2) = sep [pprParendLPat p1, pprParendLPat p2]
352 353 354 355 356
pprConArgs (RecCon rpats)   = ppr rpats

instance (OutputableBndr id, Outputable arg)
      => Outputable (HsRecFields id arg) where
  ppr (HsRecFields { rec_flds = flds, rec_dotdot = Nothing })
Ian Lynagh's avatar
Ian Lynagh committed
357
        = braces (fsep (punctuate comma (map ppr flds)))
358
  ppr (HsRecFields { rec_flds = flds, rec_dotdot = Just n })
Ian Lynagh's avatar
Ian Lynagh committed
359 360 361
        = braces (fsep (punctuate comma (map ppr (take n flds) ++ [dotdot])))
        where
          dotdot = ptext (sLit "..") <+> ifPprDebug (ppr (drop n flds))
362 363 364

instance (OutputableBndr id, Outputable arg)
      => Outputable (HsRecField id arg) where
Ian Lynagh's avatar
Ian Lynagh committed
365 366
  ppr (HsRecField { hsRecFieldId = f, hsRecFieldArg = arg,
                    hsRecPun = pun })
367
    = ppr f <+> (ppUnless pun $ equals <+> ppr arg)
368

Austin Seipp's avatar
Austin Seipp committed
369 370 371 372 373 374 375
{-
************************************************************************
*                                                                      *
*              Building patterns
*                                                                      *
************************************************************************
-}
376

377
mkPrefixConPat :: DataCon -> [OutPat id] -> [Type] -> OutPat id
378
-- Make a vanilla Prefix constructor pattern
379
mkPrefixConPat dc pats tys
Gergő Érdi's avatar
Gergő Érdi committed
380
  = noLoc $ ConPatOut { pat_con = noLoc (RealDataCon dc), pat_tvs = [], pat_dicts = [],
Ian Lynagh's avatar
Ian Lynagh committed
381
                        pat_binds = emptyTcEvBinds, pat_args = PrefixCon pats,
382
                        pat_arg_tys = tys, pat_wrap = idHsWrapper }
383

384
mkNilPat :: Type -> OutPat id
385
mkNilPat ty = mkPrefixConPat nilDataCon [] [ty]
386

387 388 389
mkCharLitPat :: String -> Char -> OutPat id
mkCharLitPat src c = mkPrefixConPat charDataCon
                                    [noLoc $ LitPat (HsCharPrim src c)] []
390

Austin Seipp's avatar
Austin Seipp committed
391 392 393 394 395 396
{-
************************************************************************
*                                                                      *
* Predicates for checking things about pattern-lists in EquationInfo   *
*                                                                      *
************************************************************************
397

398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419
\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.

420
The 1.3 report defines what ``irrefutable'' and ``failure-free'' patterns are.
Austin Seipp's avatar
Austin Seipp committed
421 422
-}

423 424 425 426 427 428 429 430
isStrictLPat :: LPat id -> Bool
isStrictLPat (L _ (ParPat p))             = isStrictLPat p
isStrictLPat (L _ (BangPat {}))           = True
isStrictLPat (L _ (TuplePat _ Unboxed _)) = True
isStrictLPat _                            = False

isStrictHsBind :: HsBind id -> Bool
-- A pattern binding with an outermost bang or unboxed tuple must be matched strictly
431
-- Defined in this module because HsPat is above HsBinds in the import graph
432 433 434 435 436
isStrictHsBind (PatBind { pat_lhs = p }) = isStrictLPat p
isStrictHsBind _                         = False

looksLazyPatBind :: HsBind id -> Bool
-- Returns True of anything *except*
Austin Seipp's avatar
Austin Seipp committed
437
--     a StrictHsBind (as above) or
438 439 440 441 442 443 444 445 446 447 448 449 450
--     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
451

452
isIrrefutableHsPat :: OutputableBndr id => LPat id -> Bool
453 454
-- (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
455 456 457
--      (NB: this is not quite the same as the (silly) defn
--      in 3.17.2 of the Haskell 98 report.)
--
458
-- isIrrefutableHsPat returns False if it's in doubt; specifically
459
-- on a ConPatIn it doesn't know the size of the constructor family
460 461 462 463
-- But if it returns True, the pattern is definitely irrefutable
isIrrefutableHsPat pat
  = go pat
  where
464
    go (L _ pat) = go1 pat
465

466 467 468
    go1 (WildPat {})        = True
    go1 (VarPat {})         = True
    go1 (LazyPat {})        = True
simonpj@microsoft.com's avatar
simonpj@microsoft.com committed
469
    go1 (BangPat pat)       = go pat
470
    go1 (CoPat _ pat _)     = go1 pat
471 472
    go1 (ParPat pat)        = go pat
    go1 (AsPat _ pat)       = go pat
473
    go1 (ViewPat _ pat _)   = go pat
474 475 476
    go1 (SigPatIn pat _)    = go pat
    go1 (SigPatOut pat _)   = go pat
    go1 (TuplePat pats _ _) = all go pats
477
    go1 (ListPat {}) = False
Ian Lynagh's avatar
Ian Lynagh committed
478
    go1 (PArrPat {})        = False     -- ?
479

Ian Lynagh's avatar
Ian Lynagh committed
480
    go1 (ConPatIn {})       = False     -- Conservative
Gergő Érdi's avatar
Gergő Érdi committed
481
    go1 (ConPatOut{ pat_con = L _ (RealDataCon con), pat_args = details })
Ian Lynagh's avatar
Ian Lynagh committed
482 483 484 485
        =  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
486 487
    go1 (ConPatOut{ pat_con = L _ (PatSynCon _pat) })
        = False -- Conservative
488

489 490 491
    go1 (LitPat {})    = False
    go1 (NPat {})      = False
    go1 (NPlusKPat {}) = False
492

gmainland's avatar
gmainland committed
493 494
    -- Both should be gotten rid of by renamer before
    -- isIrrefutablePat is called
Austin Seipp's avatar
Austin Seipp committed
495
    go1 (SplicePat {})     = urk pat
496 497

    urk pat = pprPanic "isIrrefutableHsPat:" (ppr pat)
498 499

hsPatNeedsParens :: Pat a -> Bool
500
hsPatNeedsParens (NPlusKPat {})      = True
gmainland's avatar
gmainland committed
501
hsPatNeedsParens (SplicePat {})      = False
502 503 504 505 506
hsPatNeedsParens (ConPatIn _ ds)     = conPatNeedsParens ds
hsPatNeedsParens p@(ConPatOut {})    = conPatNeedsParens (pat_args p)
hsPatNeedsParens (SigPatIn {})       = True
hsPatNeedsParens (SigPatOut {})      = True
hsPatNeedsParens (ViewPat {})        = True
507
hsPatNeedsParens (CoPat _ p _)       = hsPatNeedsParens p
508 509 510 511 512 513 514 515
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
516 517 518
hsPatNeedsParens (PArrPat {})        = False
hsPatNeedsParens (LitPat {})         = False
hsPatNeedsParens (NPat {})           = False
519 520 521

conPatNeedsParens :: HsConDetails a b -> Bool
conPatNeedsParens (PrefixCon args) = not (null args)
522 523
conPatNeedsParens (InfixCon {})    = True
conPatNeedsParens (RecCon {})      = True