{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow]
                                      -- in module Language.Haskell.Syntax.Extension
{-# LANGUAGE ViewPatterns #-}


{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

\section[HsBinds]{Abstract syntax: top-level bindings and signatures}

Datatype for: @BindGroup@, @Bind@, @Sig@, @Bind@.
-}

-- See Note [Language.Haskell.Syntax.* Hierarchy] for why not GHC.Hs.*
module Language.Haskell.Syntax.Binds where

import {-# SOURCE #-} Language.Haskell.Syntax.Expr
  ( LHsExpr
  , MatchGroup
  , GRHSs )
import {-# SOURCE #-} Language.Haskell.Syntax.Pat
  ( LPat )

import Language.Haskell.Syntax.Extension
import Language.Haskell.Syntax.Type

import GHC.Types.Fixity (Fixity)
import GHC.Types.Basic (InlinePragma)

import GHC.Data.BooleanFormula (LBooleanFormula)
import GHC.Types.SourceText (StringLiteral)

import Data.Void
import Data.Bool
import Data.Maybe

{-
************************************************************************
*                                                                      *
\subsection{Bindings: @BindGroup@}
*                                                                      *
************************************************************************

Global bindings (where clauses)
-}

-- During renaming, we need bindings where the left-hand sides
-- have been renamed but the right-hand sides have not.
-- Other than during renaming, these will be the same.

-- | Haskell Local Bindings
type HsLocalBinds id = HsLocalBindsLR id id

-- | Located Haskell local bindings
type LHsLocalBinds id = XRec id (HsLocalBinds id)

-- | Haskell Local Bindings with separate Left and Right identifier types
--
-- Bindings in a 'let' expression
-- or a 'where' clause
data HsLocalBindsLR idL idR
  = HsValBinds
        (XHsValBinds idL idR)
        (HsValBindsLR idL idR)
      -- ^ Haskell Value Bindings

         -- There should be no pattern synonyms in the HsValBindsLR
         -- These are *local* (not top level) bindings
         -- The parser accepts them, however, leaving the
         -- renamer to report them

  | HsIPBinds
        (XHsIPBinds idL idR)
        (HsIPBinds idR)
      -- ^ Haskell Implicit Parameter Bindings

  | EmptyLocalBinds (XEmptyLocalBinds idL idR)
      -- ^ Empty Local Bindings

  | XHsLocalBindsLR
        !(XXHsLocalBindsLR idL idR)

type LHsLocalBindsLR idL idR = XRec idL (HsLocalBindsLR idL idR)


-- | Haskell Value Bindings
type HsValBinds id = HsValBindsLR id id

-- | Haskell Value bindings with separate Left and Right identifier types
-- (not implicit parameters)
-- Used for both top level and nested bindings
-- May contain pattern synonym bindings
data HsValBindsLR idL idR
  = -- | Value Bindings In
    --
    -- Before renaming RHS; idR is always RdrName
    -- Not dependency analysed
    -- Recursive by default
    ValBinds
        (XValBinds idL idR)
        (LHsBindsLR idL idR) [LSig idR]

    -- | Value Bindings Out
    --
    -- After renaming RHS; idR can be Name or Id Dependency analysed,
    -- later bindings in the list may depend on earlier ones.
  | XValBindsLR
      !(XXValBindsLR idL idR)

-- ---------------------------------------------------------------------

-- | Located Haskell Binding
type LHsBind  id = LHsBindLR  id id

-- | Located Haskell Bindings
type LHsBinds id = LHsBindsLR id id

-- | Haskell Binding
type HsBind   id = HsBindLR   id id

-- | Located Haskell Bindings with separate Left and Right identifier types
type LHsBindsLR idL idR = [LHsBindLR idL idR]

-- | Located Haskell Binding with separate Left and Right identifier types
type LHsBindLR  idL idR = XRec idL (HsBindLR idL idR)

{- Note [FunBind vs PatBind]
   ~~~~~~~~~~~~~~~~~~~~~~~~~
The distinction between FunBind and PatBind is a bit subtle. FunBind covers
patterns which resemble function bindings and simple variable bindings.

    f x = e
    f !x = e
    f = e
    !x = e          -- FunRhs has SrcStrict
    x `f` y = e     -- FunRhs has Infix

The actual patterns and RHSs of a FunBind are encoding in fun_matches.
The m_ctxt field of each Match in fun_matches will be FunRhs and carries
two bits of information about the match,

  * The mc_fixity field on each Match describes the fixity of the
    function binder in that match.  E.g. this is legal:
         f True False  = e1
         True `f` True = e2

  * The mc_strictness field is used /only/ for nullary FunBinds: ones
    with one Match, which has no pats. For these, it describes whether
    the match is decorated with a bang (e.g. `!x = e`).

By contrast, PatBind represents data constructor patterns, as well as a few
other interesting cases. Namely,

    Just x = e
    (x) = e
    x :: Ty = e

Note [Multiplicity annotations]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Multiplicity annotations are stored in the pat_mult field on PatBinds,
represented by the HsMultAnn data type

  HsNoMultAnn <=> no annotation in the source file
  HsPct1Ann   <=> the %1 annotation
  HsMultAnn   <=> the %t annotation, where `t` is some type

In case of HsNoMultAnn the typechecker infers a multiplicity.

We don't need to store a multiplicity on FunBinds:
- let %1 x = … is parsed as a PatBind. So we don't need an annotation before
  typechecking.
- the multiplicity that the typechecker infers is stored in the binder's Var for
  the desugarer to use. It's only relevant for strict FunBinds, see Wrinkle 1 in
  Note [Desugar Strict binds] in GHC.HsToCore.Binds as, in Core, let expressions
  don't have multiplicity annotations.
-}

-- | Haskell Binding with separate Left and Right id's
data HsBindLR idL idR
  = -- | Function-like Binding
    --
    -- FunBind is used for both functions     @f x = e@
    -- and variables                          @f = \x -> e@
    -- and strict variables                   @!x = x + 1@
    --
    -- Reason 1: Special case for type inference: see 'GHC.Tc.Gen.Bind.tcMonoBinds'.
    --
    -- Reason 2: Instance decls can only have FunBinds, which is convenient.
    --           If you change this, you'll need to change e.g. rnMethodBinds
    --
    -- But note that the form                 @f :: a->a = ...@
    -- parses as a pattern binding, just like
    --                                        @(f :: a -> a) = ... @
    --
    -- Strict bindings have their strictness recorded in the 'SrcStrictness' of their
    -- 'MatchContext'. See Note [FunBind vs PatBind] for
    -- details about the relationship between FunBind and PatBind.
    --
    --  'GHC.Parser.Annotation.AnnKeywordId's
    --
    --  - 'GHC.Parser.Annotation.AnnFunId', attached to each element of fun_matches
    --
    --  - 'GHC.Parser.Annotation.AnnEqual','GHC.Parser.Annotation.AnnWhere',
    --    'GHC.Parser.Annotation.AnnOpen','GHC.Parser.Annotation.AnnClose',

    -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
    FunBind {

        forall idL idR. HsBindLR idL idR -> XFunBind idL idR
fun_ext :: XFunBind idL idR,

        forall idL idR. HsBindLR idL idR -> LIdP idL
fun_id :: LIdP idL, -- Note [fun_id in Match] in GHC.Hs.Expr

        forall idL idR. HsBindLR idL idR -> MatchGroup idR (LHsExpr idR)
fun_matches :: MatchGroup idR (LHsExpr idR)  -- ^ The payload

    }

  -- | Pattern Binding
  --
  -- The pattern is never a simple variable;
  -- That case is done by FunBind.
  -- See Note [FunBind vs PatBind] for details about the
  -- relationship between FunBind and PatBind.

  --
  --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnBang',
  --       'GHC.Parser.Annotation.AnnEqual','GHC.Parser.Annotation.AnnWhere',
  --       'GHC.Parser.Annotation.AnnOpen','GHC.Parser.Annotation.AnnClose',

  -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
  | PatBind {
        forall idL idR. HsBindLR idL idR -> XPatBind idL idR
pat_ext    :: XPatBind idL idR,
        forall idL idR. HsBindLR idL idR -> LPat idL
pat_lhs    :: LPat idL,
        forall idL idR. HsBindLR idL idR -> HsMultAnn idL
pat_mult   :: HsMultAnn idL,
        -- ^ See Note [Multiplicity annotations].
        forall idL idR. HsBindLR idL idR -> GRHSs idR (LHsExpr idR)
pat_rhs    :: GRHSs idR (LHsExpr idR)
    }

  -- | Variable Binding
  --
  -- Dictionary binding and suchlike.
  -- All VarBinds are introduced by the type checker
  | VarBind {
        forall idL idR. HsBindLR idL idR -> XVarBind idL idR
var_ext    :: XVarBind idL idR,
        forall idL idR. HsBindLR idL idR -> IdP idL
var_id     :: IdP idL,
        forall idL idR. HsBindLR idL idR -> LHsExpr idR
var_rhs    :: LHsExpr idR    -- ^ Located only for consistency
    }

  -- | Patterns Synonym Binding
  | PatSynBind
        (XPatSynBind idL idR)
        (PatSynBind idL idR)
        -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnPattern',
        --          'GHC.Parser.Annotation.AnnLarrow','GHC.Parser.Annotation.AnnEqual',
        --          'GHC.Parser.Annotation.AnnWhere'
        --          'GHC.Parser.Annotation.AnnOpen' @'{'@,'GHC.Parser.Annotation.AnnClose' @'}'@

        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

  | XHsBindsLR !(XXHsBindsLR idL idR)


-- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnPattern',
--             'GHC.Parser.Annotation.AnnEqual','GHC.Parser.Annotation.AnnLarrow',
--             'GHC.Parser.Annotation.AnnWhere','GHC.Parser.Annotation.AnnOpen' @'{'@,
--             'GHC.Parser.Annotation.AnnClose' @'}'@,

-- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

-- | Pattern Synonym binding
data PatSynBind idL idR
  = PSB { forall idL idR. PatSynBind idL idR -> XPSB idL idR
psb_ext  :: XPSB idL idR,
          forall idL idR. PatSynBind idL idR -> LIdP idL
psb_id   :: LIdP idL,                -- ^ Name of the pattern synonym
          forall idL idR. PatSynBind idL idR -> HsPatSynDetails idR
psb_args :: HsPatSynDetails idR,     -- ^ Formal parameter names
          forall idL idR. PatSynBind idL idR -> LPat idR
psb_def  :: LPat idR,                -- ^ Right-hand side
          forall idL idR. PatSynBind idL idR -> HsPatSynDir idR
psb_dir  :: HsPatSynDir idR          -- ^ Directionality
     }
   | XPatSynBind !(XXPatSynBind idL idR)

-- | Multiplicity annotations, on binders, are always resolved (to a unification
-- variable if there is no annotation) during type-checking. The resolved
-- multiplicity is stored in the extension fields.
data HsMultAnn pass
  = HsNoMultAnn !(XNoMultAnn pass)
  | HsPct1Ann   !(XPct1Ann pass)
  | HsMultAnn   !(XMultAnn pass) (LHsType (NoGhcTc pass))
  | XMultAnn    !(XXMultAnn pass)

type family XNoMultAnn p
type family XPct1Ann   p
type family XMultAnn   p
type family XXMultAnn  p

{-
************************************************************************
*                                                                      *
                Implicit parameter bindings
*                                                                      *
************************************************************************
-}

-- | Haskell Implicit Parameter Bindings
data HsIPBinds id
  = IPBinds
        (XIPBinds id)
        [LIPBind id]
        -- TcEvBinds       -- Only in typechecker output; binds
        --                 -- uses of the implicit parameters
  | XHsIPBinds !(XXHsIPBinds id)


-- | Located Implicit Parameter Binding
type LIPBind id = XRec id (IPBind id)
-- ^ May have 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnSemi' when in a
--   list

-- For details on above see Note [exact print annotations] in GHC.Parser.Annotation

-- | Implicit parameter bindings.
--
-- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnEqual'

-- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
data IPBind id
  = IPBind
        (XCIPBind id)
        (XRec id HsIPName)
        (LHsExpr id)
  | XIPBind !(XXIPBind id)

{-
************************************************************************
*                                                                      *
\subsection{@Sig@: type signatures and value-modifying user pragmas}
*                                                                      *
************************************************************************

It is convenient to lump ``value-modifying'' user-pragmas (e.g.,
``specialise this function to these four types...'') in with type
signatures.  Then all the machinery to move them into place, etc.,
serves for both.
-}

-- | Located Signature
type LSig pass = XRec pass (Sig pass)

-- | Signatures and pragmas
data Sig pass
  =   -- | An ordinary type signature
      --
      -- > f :: Num a => a -> a
      --
      -- After renaming, this list of Names contains the named
      -- wildcards brought into scope by this signature. For a signature
      -- @_ -> _a -> Bool@, the renamer will leave the unnamed wildcard @_@
      -- untouched, and the named wildcard @_a@ is then replaced with
      -- fresh meta vars in the type. Their names are stored in the type
      -- signature that brought them into scope, in this third field to be
      -- more specific.
      --
      --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDcolon',
      --          'GHC.Parser.Annotation.AnnComma'

      -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
    TypeSig
       (XTypeSig pass)
       [LIdP pass]           -- LHS of the signature; e.g.  f,g,h :: blah
       (LHsSigWcType pass)   -- RHS of the signature; can have wildcards

      -- | A pattern synonym type signature
      --
      -- > pattern Single :: () => (Show a) => a -> [a]
      --
      --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnPattern',
      --           'GHC.Parser.Annotation.AnnDcolon','GHC.Parser.Annotation.AnnForall'
      --           'GHC.Parser.Annotation.AnnDot','GHC.Parser.Annotation.AnnDarrow'

      -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
  | PatSynSig (XPatSynSig pass) [LIdP pass] (LHsSigType pass)
      -- P :: forall a b. Req => Prov => ty

      -- | A signature for a class method
      --   False: ordinary class-method signature
      --   True:  generic-default class method signature
      -- e.g.   class C a where
      --          op :: a -> a                   -- Ordinary
      --          default op :: Eq a => a -> a   -- Generic default
      -- No wildcards allowed here
      --
      --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDefault',
      --           'GHC.Parser.Annotation.AnnDcolon'
  | ClassOpSig (XClassOpSig pass) Bool [LIdP pass] (LHsSigType pass)

        -- | An ordinary fixity declaration
        --
        -- >     infixl 8 ***
        --
        --
        --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnInfix',
        --           'GHC.Parser.Annotation.AnnVal'

        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
  | FixSig (XFixSig pass) (FixitySig pass)

        -- | An inline pragma
        --
        -- > {#- INLINE f #-}
        --
        --  - 'GHC.Parser.Annotation.AnnKeywordId' :
        --       'GHC.Parser.Annotation.AnnOpen' @'{-\# INLINE'@ and @'['@,
        --       'GHC.Parser.Annotation.AnnClose','GHC.Parser.Annotation.AnnOpen',
        --       'GHC.Parser.Annotation.AnnVal','GHC.Parser.Annotation.AnnTilde',
        --       'GHC.Parser.Annotation.AnnClose'

        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
  | InlineSig   (XInlineSig pass)
                (LIdP pass)        -- Function name
                InlinePragma       -- Never defaultInlinePragma

        -- | A specialisation pragma
        --
        -- > {-# SPECIALISE f :: Int -> Int #-}
        --
        --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen',
        --      'GHC.Parser.Annotation.AnnOpen' @'{-\# SPECIALISE'@ and @'['@,
        --      'GHC.Parser.Annotation.AnnTilde',
        --      'GHC.Parser.Annotation.AnnVal',
        --      'GHC.Parser.Annotation.AnnClose' @']'@ and @'\#-}'@,
        --      'GHC.Parser.Annotation.AnnDcolon'

        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
  | SpecSig     (XSpecSig pass)
                (LIdP pass)        -- Specialise a function or datatype  ...
                [LHsSigType pass]  -- ... to these types
                InlinePragma       -- The pragma on SPECIALISE_INLINE form.
                                   -- If it's just defaultInlinePragma, then we said
                                   --    SPECIALISE, not SPECIALISE_INLINE

        -- | A specialisation pragma for instance declarations only
        --
        -- > {-# SPECIALISE instance Eq [Int] #-}
        --
        -- (Class tys); should be a specialisation of the
        -- current instance declaration
        --
        --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen',
        --      'GHC.Parser.Annotation.AnnInstance','GHC.Parser.Annotation.AnnClose'

        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
  | SpecInstSig (XSpecInstSig pass) (LHsSigType pass)

        -- | A minimal complete definition pragma
        --
        -- > {-# MINIMAL a | (b, c | (d | e)) #-}
        --
        --  - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen',
        --      'GHC.Parser.Annotation.AnnVbar','GHC.Parser.Annotation.AnnComma',
        --      'GHC.Parser.Annotation.AnnClose'

        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
  | MinimalSig (XMinimalSig pass) (LBooleanFormula (LIdP pass))

        -- | A "set cost centre" pragma for declarations
        --
        -- > {-# SCC funName #-}
        --
        -- or
        --
        -- > {-# SCC funName "cost_centre_name" #-}

  | SCCFunSig  (XSCCFunSig pass)
               (LIdP pass)    -- Function name
               (Maybe (XRec pass StringLiteral))
       -- | A complete match pragma
       --
       -- > {-# COMPLETE C, D [:: T] #-}
       --
       -- Used to inform the pattern match checker about additional
       -- complete matchings which, for example, arise from pattern
       -- synonym definitions.
  | CompleteMatchSig (XCompleteMatchSig pass)
                     [LIdP pass]
                     (Maybe (LIdP pass))
  | XSig !(XXSig pass)

-- | Located Fixity Signature
type LFixitySig pass = XRec pass (FixitySig pass)

-- | Fixity Signature
data FixitySig pass = FixitySig (XFixitySig pass) [LIdP pass] Fixity
                    | XFixitySig !(XXFixitySig pass)

isFixityLSig :: forall p. UnXRec p => LSig p -> Bool
isFixityLSig :: forall p. UnXRec p => LSig p -> Bool
isFixityLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> FixSig {}) = Bool
True
isFixityLSig LSig p
_                 = Bool
False

isTypeLSig :: forall p. UnXRec p => LSig p -> Bool  -- Type signatures
isTypeLSig :: forall p. UnXRec p => LSig p -> Bool
isTypeLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> TypeSig {})    = Bool
True
isTypeLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> ClassOpSig {}) = Bool
True
isTypeLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> XSig {})       = Bool
True
isTypeLSig LSig p
_                    = Bool
False

isSpecLSig :: forall p. UnXRec p => LSig p -> Bool
isSpecLSig :: forall p. UnXRec p => LSig p -> Bool
isSpecLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> SpecSig {}) = Bool
True
isSpecLSig LSig p
_                 = Bool
False

isSpecInstLSig :: forall p. UnXRec p => LSig p -> Bool
isSpecInstLSig :: forall p. UnXRec p => LSig p -> Bool
isSpecInstLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> SpecInstSig {}) = Bool
True
isSpecInstLSig LSig p
_                      = Bool
False

isPragLSig :: forall p. UnXRec p => LSig p -> Bool
-- Identifies pragmas
isPragLSig :: forall p. UnXRec p => LSig p -> Bool
isPragLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> SpecSig {})   = Bool
True
isPragLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> InlineSig {}) = Bool
True
isPragLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> SCCFunSig {}) = Bool
True
isPragLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> CompleteMatchSig {}) = Bool
True
isPragLSig LSig p
_                    = Bool
False

isInlineLSig :: forall p. UnXRec p => LSig p -> Bool
-- Identifies inline pragmas
isInlineLSig :: forall p. UnXRec p => LSig p -> Bool
isInlineLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> InlineSig {}) = Bool
True
isInlineLSig LSig p
_                    = Bool
False

isMinimalLSig :: forall p. UnXRec p => LSig p -> Bool
isMinimalLSig :: forall p. UnXRec p => LSig p -> Bool
isMinimalLSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> MinimalSig {}) = Bool
True
isMinimalLSig LSig p
_                               = Bool
False

isSCCFunSig :: forall p. UnXRec p => LSig p -> Bool
isSCCFunSig :: forall p. UnXRec p => LSig p -> Bool
isSCCFunSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> SCCFunSig {}) = Bool
True
isSCCFunSig LSig p
_                    = Bool
False

isCompleteMatchSig :: forall p. UnXRec p => LSig p -> Bool
isCompleteMatchSig :: forall p. UnXRec p => LSig p -> Bool
isCompleteMatchSig (forall p a. UnXRec p => XRec p a -> a
unXRec @p -> CompleteMatchSig {} ) = Bool
True
isCompleteMatchSig LSig p
_                            = Bool
False

{-
************************************************************************
*                                                                      *
\subsection[PatSynBind]{A pattern synonym definition}
*                                                                      *
************************************************************************
-}

-- | Haskell Pattern Synonym Details
type HsPatSynDetails pass = HsConDetails Void (LIdP pass) [RecordPatSynField pass]

-- See Note [Record PatSyn Fields]
-- | Record Pattern Synonym Field
data RecordPatSynField pass
  = RecordPatSynField
      { forall pass. RecordPatSynField pass -> FieldOcc pass
recordPatSynField :: FieldOcc pass
      -- ^ Field label visible in rest of the file
      , forall pass. RecordPatSynField pass -> LIdP pass
recordPatSynPatVar :: LIdP pass
      -- ^ Filled in by renamer, the name used internally by the pattern
      }


{-
Note [Record PatSyn Fields]
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Consider the following two pattern synonyms.

  pattern P x y = ([x,True], [y,'v'])
  pattern Q{ x, y } =([x,True], [y,'v'])

In P, we just have two local binders, x and y.

In Q, we have local binders but also top-level record selectors
  x :: ([Bool], [Char]) -> Bool
  y :: ([Bool], [Char]) -> Char

Both are recorded in the `RecordPatSynField`s for `x` and `y`:
* recordPatSynField: the top-level record selector
* recordPatSynPatVar: the local `x`, bound only in the RHS of the pattern synonym.

It would make sense to support record-like syntax

  pattern Q{ x=x1, y=y1 } = ([x1,True], [y1,'v'])

when we have a different name for the local and top-level binder,
making the distinction between the two names clear.

-}

-- | Haskell Pattern Synonym Direction
data HsPatSynDir id
  = Unidirectional
  | ImplicitBidirectional
  | ExplicitBidirectional (MatchGroup id (LHsExpr id))