Parser.y.pp 89.8 KB
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--                                                              -*-haskell-*-
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-- ---------------------------------------------------------------------------
-- (c) The University of Glasgow 1997-2003
---
-- The GHC grammar.
--
-- Author(s): Simon Marlow, Sven Panne 1997, 1998, 1999
-- ---------------------------------------------------------------------------

{
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{-# LANGUAGE BangPatterns #-} -- required for versions of Happy before 1.18.6
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{-# OPTIONS -Wwarn -w #-}
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-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and fix
-- any warnings in the module. See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
-- for details

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{-# OPTIONS_GHC -O0 -fno-ignore-interface-pragmas #-}
{-
Careful optimisation of the parser: we don't want to throw everything
at it, because that takes too long and doesn't buy much, but we do want
to inline certain key external functions, so we instruct GHC not to
throw away inlinings as it would normally do in -O0 mode.
-}

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module Parser ( parseModule, parseStmt, parseIdentifier, parseType,
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                parseHeader ) where
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import HsSyn
import RdrHsSyn
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import HscTypes         ( IsBootInterface, WarningTxt(..) )
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import Lexer
import RdrName
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import TysPrim          ( eqPrimTyCon )
import TysWiredIn       ( unitTyCon, unitDataCon, tupleTyCon, tupleCon, nilDataCon,
                          unboxedSingletonTyCon, unboxedSingletonDataCon,
                          listTyCon_RDR, parrTyCon_RDR, consDataCon_RDR, eqTyCon_RDR )
import Type             ( funTyCon )
import ForeignCall      ( Safety(..), CExportSpec(..), CLabelString,
                          CCallConv(..), CCallTarget(..), defaultCCallConv
                        )
import OccName          ( varName, dataName, tcClsName, tvName )
import DataCon          ( DataCon, dataConName )
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import SrcLoc
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import Module
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import StaticFlags      ( opt_SccProfilingOn, opt_Hpc )
import Type             ( Kind, liftedTypeKind, unliftedTypeKind )
import Coercion         ( mkArrowKind )
import Class            ( FunDep )
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import BasicTypes
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import DynFlags
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import OrdList
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import HaddockUtils
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import FastString
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import Maybes           ( orElse )
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import Outputable
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import Control.Monad    ( unless )
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import GHC.Exts
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import Data.Char
import Control.Monad    ( mplus )
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}

{-
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-----------------------------------------------------------------------------
24 Februar 2006

Conflicts: 33 shift/reduce
           1 reduce/reduce

The reduce/reduce conflict is weird.  It's between tyconsym and consym, and I
would think the two should never occur in the same context.

  -=chak

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-----------------------------------------------------------------------------
31 December 2006

Conflicts: 34 shift/reduce
           1 reduce/reduce

The reduce/reduce conflict is weird.  It's between tyconsym and consym, and I
would think the two should never occur in the same context.

  -=chak

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-----------------------------------------------------------------------------
6 December 2006

Conflicts: 32 shift/reduce
           1 reduce/reduce

The reduce/reduce conflict is weird.  It's between tyconsym and consym, and I
would think the two should never occur in the same context.

  -=chak

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-----------------------------------------------------------------------------
26 July 2006

Conflicts: 37 shift/reduce
           1 reduce/reduce

The reduce/reduce conflict is weird.  It's between tyconsym and consym, and I
would think the two should never occur in the same context.

  -=chak

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-----------------------------------------------------------------------------
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Conflicts: 38 shift/reduce (1.25)
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10 for abiguity in 'if x then y else z + 1'             [State 178]
        (shift parses as 'if x then y else (z + 1)', as per longest-parse rule)
        10 because op might be: : - ! * . `x` VARSYM CONSYM QVARSYM QCONSYM
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1 for ambiguity in 'if x then y else z :: T'            [State 178]
        (shift parses as 'if x then y else (z :: T)', as per longest-parse rule)
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4 for ambiguity in 'if x then y else z -< e'            [State 178]
        (shift parses as 'if x then y else (z -< T)', as per longest-parse rule)
        There are four such operators: -<, >-, -<<, >>-
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2 for ambiguity in 'case v of { x :: T -> T ... } '     [States 11, 253]
        Which of these two is intended?
          case v of
            (x::T) -> T         -- Rhs is T
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    or
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          case v of
            (x::T -> T) -> ..   -- Rhs is ...
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10 for ambiguity in 'e :: a `b` c'.  Does this mean     [States 11, 253]
        (e::a) `b` c, or 
        (e :: (a `b` c))
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    As well as `b` we can have !, VARSYM, QCONSYM, and CONSYM, hence 5 cases
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    Same duplication between states 11 and 253 as the previous case
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1 for ambiguity in 'let ?x ...'                         [State 329]
        the parser can't tell whether the ?x is the lhs of a normal binding or
        an implicit binding.  Fortunately resolving as shift gives it the only
        sensible meaning, namely the lhs of an implicit binding.
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1 for ambiguity in '{-# RULES "name" [ ... #-}          [State 382]
        we don't know whether the '[' starts the activation or not: it
        might be the start of the declaration with the activation being
        empty.  --SDM 1/4/2002
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1 for ambiguity in '{-# RULES "name" forall = ... #-}'  [State 474]
        since 'forall' is a valid variable name, we don't know whether
        to treat a forall on the input as the beginning of a quantifier
        or the beginning of the rule itself.  Resolving to shift means
        it's always treated as a quantifier, hence the above is disallowed.
        This saves explicitly defining a grammar for the rule lhs that
        doesn't include 'forall'.
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1 for ambiguity when the source file starts with "-- | doc". We need another
  token of lookahead to determine if a top declaration or the 'module' keyword
  follows. Shift parses as if the 'module' keyword follows.   

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-- ---------------------------------------------------------------------------
-- Adding location info

This is done in a stylised way using the three macros below, L0, L1
and LL.  Each of these macros can be thought of as having type

   L0, L1, LL :: a -> Located a

They each add a SrcSpan to their argument.

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   L0   adds 'noSrcSpan', used for empty productions
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     -- This doesn't seem to work anymore -=chak
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   L1   for a production with a single token on the lhs.  Grabs the SrcSpan
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        from that token.
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   LL   for a production with >1 token on the lhs.  Makes up a SrcSpan from
        the first and last tokens.

These suffice for the majority of cases.  However, we must be
especially careful with empty productions: LL won't work if the first
or last token on the lhs can represent an empty span.  In these cases,
we have to calculate the span using more of the tokens from the lhs, eg.

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        | 'newtype' tycl_hdr '=' newconstr deriving
                { L (comb3 $1 $4 $5)
                    (mkTyData NewType (unLoc $2) [$4] (unLoc $5)) }
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We provide comb3 and comb4 functions which are useful in such cases.

Be careful: there's no checking that you actually got this right, the
only symptom will be that the SrcSpans of your syntax will be
incorrect.

/*
 * We must expand these macros *before* running Happy, which is why this file is
 * Parser.y.pp rather than just Parser.y - we run the C pre-processor first.
 */
#define L0   L noSrcSpan
#define L1   sL (getLoc $1)
#define LL   sL (comb2 $1 $>)

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

-}

%token
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 '_'            { L _ ITunderscore }            -- Haskell keywords
 'as'           { L _ ITas }
 'case'         { L _ ITcase }          
 'class'        { L _ ITclass } 
 'data'         { L _ ITdata } 
 'default'      { L _ ITdefault }
 'deriving'     { L _ ITderiving }
 'do'           { L _ ITdo }
 'else'         { L _ ITelse }
 'hiding'       { L _ IThiding }
 'if'           { L _ ITif }
 'import'       { L _ ITimport }
 'in'           { L _ ITin }
 'infix'        { L _ ITinfix }
 'infixl'       { L _ ITinfixl }
 'infixr'       { L _ ITinfixr }
 'instance'     { L _ ITinstance }
 'let'          { L _ ITlet }
 'module'       { L _ ITmodule }
 'newtype'      { L _ ITnewtype }
 'of'           { L _ ITof }
 'qualified'    { L _ ITqualified }
 'then'         { L _ ITthen }
 'type'         { L _ ITtype }
 'where'        { L _ ITwhere }
 '_scc_'        { L _ ITscc }         -- ToDo: remove

 'forall'       { L _ ITforall }                -- GHC extension keywords
 'foreign'      { L _ ITforeign }
 'export'       { L _ ITexport }
 'label'        { L _ ITlabel } 
 'dynamic'      { L _ ITdynamic }
 'safe'         { L _ ITsafe }
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 'interruptible' { L _ ITinterruptible }
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 'unsafe'       { L _ ITunsafe }
 'mdo'          { L _ ITmdo }
 'family'       { L _ ITfamily }
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 'stdcall'      { L _ ITstdcallconv }
 'ccall'        { L _ ITccallconv }
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 'prim'         { L _ ITprimcallconv }
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 'proc'         { L _ ITproc }          -- for arrow notation extension
 'rec'          { L _ ITrec }           -- for arrow notation extension
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 'group'    { L _ ITgroup }     -- for list transform extension
 'by'       { L _ ITby }        -- for list transform extension
 'using'    { L _ ITusing }     -- for list transform extension
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 '{-# INLINE'             { L _ (ITinline_prag _ _) }
 '{-# SPECIALISE'         { L _ ITspec_prag }
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 '{-# SPECIALISE_INLINE'  { L _ (ITspec_inline_prag _) }
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 '{-# SOURCE'                                   { L _ ITsource_prag }
 '{-# RULES'                                    { L _ ITrules_prag }
 '{-# CORE'                                     { L _ ITcore_prag }              -- hdaume: annotated core
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 '{-# SCC'                { L _ ITscc_prag }
 '{-# GENERATED'          { L _ ITgenerated_prag }
 '{-# DEPRECATED'         { L _ ITdeprecated_prag }
 '{-# WARNING'            { L _ ITwarning_prag }
 '{-# UNPACK'             { L _ ITunpack_prag }
 '{-# ANN'                { L _ ITann_prag }
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 '{-# VECTORISE'          { L _ ITvect_prag }
 '{-# VECTORISE_SCALAR'   { L _ ITvect_scalar_prag }
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 '{-# NOVECTORISE'        { L _ ITnovect_prag }
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 '#-}'                                          { L _ ITclose_prag }

 '..'           { L _ ITdotdot }                        -- reserved symbols
 ':'            { L _ ITcolon }
 '::'           { L _ ITdcolon }
 '='            { L _ ITequal }
 '\\'           { L _ ITlam }
 '|'            { L _ ITvbar }
 '<-'           { L _ ITlarrow }
 '->'           { L _ ITrarrow }
 '@'            { L _ ITat }
 '~'            { L _ ITtilde }
 '~#'           { L _ ITtildehsh }
 '=>'           { L _ ITdarrow }
 '-'            { L _ ITminus }
 '!'            { L _ ITbang }
 '*'            { L _ ITstar }
 '-<'           { L _ ITlarrowtail }            -- for arrow notation
 '>-'           { L _ ITrarrowtail }            -- for arrow notation
 '-<<'          { L _ ITLarrowtail }            -- for arrow notation
 '>>-'          { L _ ITRarrowtail }            -- for arrow notation
 '.'            { L _ ITdot }

 '{'            { L _ ITocurly }                        -- special symbols
 '}'            { L _ ITccurly }
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 '{|'           { L _ ITocurlybar }
 '|}'           { L _ ITccurlybar }
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 vocurly        { L _ ITvocurly } -- virtual open curly (from layout)
 vccurly        { L _ ITvccurly } -- virtual close curly (from layout)
 '['            { L _ ITobrack }
 ']'            { L _ ITcbrack }
 '[:'           { L _ ITopabrack }
 ':]'           { L _ ITcpabrack }
 '('            { L _ IToparen }
 ')'            { L _ ITcparen }
 '(#'           { L _ IToubxparen }
 '#)'           { L _ ITcubxparen }
 '(|'           { L _ IToparenbar }
 '|)'           { L _ ITcparenbar }
 ';'            { L _ ITsemi }
 ','            { L _ ITcomma }
 '`'            { L _ ITbackquote }

 VARID          { L _ (ITvarid    _) }          -- identifiers
 CONID          { L _ (ITconid    _) }
 VARSYM         { L _ (ITvarsym   _) }
 CONSYM         { L _ (ITconsym   _) }
 QVARID         { L _ (ITqvarid   _) }
 QCONID         { L _ (ITqconid   _) }
 QVARSYM        { L _ (ITqvarsym  _) }
 QCONSYM        { L _ (ITqconsym  _) }
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 PREFIXQVARSYM  { L _ (ITprefixqvarsym  _) }
 PREFIXQCONSYM  { L _ (ITprefixqconsym  _) }
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 IPDUPVARID     { L _ (ITdupipvarid   _) }              -- GHC extension

 CHAR           { L _ (ITchar     _) }
 STRING         { L _ (ITstring   _) }
 INTEGER        { L _ (ITinteger  _) }
 RATIONAL       { L _ (ITrational _) }
                    
 PRIMCHAR       { L _ (ITprimchar   _) }
 PRIMSTRING     { L _ (ITprimstring _) }
 PRIMINTEGER    { L _ (ITprimint    _) }
 PRIMWORD       { L _ (ITprimword  _) }
 PRIMFLOAT      { L _ (ITprimfloat  _) }
 PRIMDOUBLE     { L _ (ITprimdouble _) }

 DOCNEXT        { L _ (ITdocCommentNext _) }
 DOCPREV        { L _ (ITdocCommentPrev _) }
 DOCNAMED       { L _ (ITdocCommentNamed _) }
 DOCSECTION     { L _ (ITdocSection _ _) }
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-- Template Haskell 
'[|'            { L _ ITopenExpQuote  }       
'[p|'           { L _ ITopenPatQuote  }      
'[t|'           { L _ ITopenTypQuote  }      
'[d|'           { L _ ITopenDecQuote  }      
'|]'            { L _ ITcloseQuote    }
TH_ID_SPLICE    { L _ (ITidEscape _)  }     -- $x
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'$('            { L _ ITparenEscape   }     -- $( exp )
TH_VAR_QUOTE    { L _ ITvarQuote      }     -- 'x
TH_TY_QUOTE     { L _ ITtyQuote       }      -- ''T
TH_QUASIQUOTE   { L _ (ITquasiQuote _) }
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%monad { P } { >>= } { return }
%lexer { lexer } { L _ ITeof }
%name parseModule module
%name parseStmt   maybe_stmt
%name parseIdentifier  identifier
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%name parseType ctype
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%partial parseHeader header
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%tokentype { (Located Token) }
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%%

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-----------------------------------------------------------------------------
-- Identifiers; one of the entry points
identifier :: { Located RdrName }
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        : qvar                          { $1 }
        | qcon                          { $1 }
        | qvarop                        { $1 }
        | qconop                        { $1 }
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    | '(' '->' ')'      { LL $ getRdrName funTyCon }
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-----------------------------------------------------------------------------
-- Module Header

-- The place for module deprecation is really too restrictive, but if it
-- was allowed at its natural place just before 'module', we get an ugly
-- s/r conflict with the second alternative. Another solution would be the
-- introduction of a new pragma DEPRECATED_MODULE, but this is not very nice,
-- either, and DEPRECATED is only expected to be used by people who really
-- know what they are doing. :-)

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module  :: { Located (HsModule RdrName) }
        : maybedocheader 'module' modid maybemodwarning maybeexports 'where' body
                {% fileSrcSpan >>= \ loc ->
                   return (L loc (HsModule (Just $3) $5 (fst $7) (snd $7) $4 $1
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                          ) )}
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        | body2
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                {% fileSrcSpan >>= \ loc ->
                   return (L loc (HsModule Nothing Nothing
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                          (fst $1) (snd $1) Nothing Nothing
                          )) }
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maybedocheader :: { Maybe LHsDocString }
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        : moduleheader            { $1 }
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        | {- empty -}             { Nothing }
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missing_module_keyword :: { () }
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        : {- empty -}                           {% pushCurrentContext }
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maybemodwarning :: { Maybe WarningTxt }
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    : '{-# DEPRECATED' strings '#-}' { Just (DeprecatedTxt $ unLoc $2) }
    | '{-# WARNING' strings '#-}'    { Just (WarningTxt $ unLoc $2) }
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    |  {- empty -}                  { Nothing }
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body    :: { ([LImportDecl RdrName], [LHsDecl RdrName]) }
        :  '{'            top '}'               { $2 }
        |      vocurly    top close             { $2 }
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body2   :: { ([LImportDecl RdrName], [LHsDecl RdrName]) }
        :  '{' top '}'                          { $2 }
        |  missing_module_keyword top close     { $2 }
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top     :: { ([LImportDecl RdrName], [LHsDecl RdrName]) }
        : importdecls                           { (reverse $1,[]) }
        | importdecls ';' cvtopdecls            { (reverse $1,$3) }
        | cvtopdecls                            { ([],$1) }
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cvtopdecls :: { [LHsDecl RdrName] }
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        : topdecls                              { cvTopDecls $1 }
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-----------------------------------------------------------------------------
-- Module declaration & imports only

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header  :: { Located (HsModule RdrName) }
        : maybedocheader 'module' modid maybemodwarning maybeexports 'where' header_body
                {% fileSrcSpan >>= \ loc ->
                   return (L loc (HsModule (Just $3) $5 $7 [] $4 $1
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                          ))}
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        | header_body2
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                {% fileSrcSpan >>= \ loc ->
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                   return (L loc (HsModule Nothing Nothing $1 [] Nothing
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                          Nothing)) }
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header_body :: { [LImportDecl RdrName] }
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        :  '{'            importdecls           { $2 }
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        |      vocurly    importdecls           { $2 }

header_body2 :: { [LImportDecl RdrName] }
        :  '{' importdecls                      { $2 }
        |  missing_module_keyword importdecls   { $2 }
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-----------------------------------------------------------------------------
-- The Export List

maybeexports :: { Maybe [LIE RdrName] }
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        :  '(' exportlist ')'                   { Just $2 }
        |  {- empty -}                          { Nothing }
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exportlist :: { [LIE RdrName] }
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        : expdoclist ',' expdoclist             { $1 ++ $3 }
        | exportlist1                           { $1 }
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exportlist1 :: { [LIE RdrName] }
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        : expdoclist export expdoclist ',' exportlist  { $1 ++ ($2 : $3) ++ $5 }
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        | expdoclist export expdoclist                 { $1 ++ ($2 : $3) }
        | expdoclist                                   { $1 }
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expdoclist :: { [LIE RdrName] }
        : exp_doc expdoclist                           { $1 : $2 }
        | {- empty -}                                  { [] }

exp_doc :: { LIE RdrName }                                                   
        : docsection    { L1 (case (unLoc $1) of (n, doc) -> IEGroup n doc) }
        | docnamed      { L1 (IEDocNamed ((fst . unLoc) $1)) } 
        | docnext       { L1 (IEDoc (unLoc $1)) }       
                       
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   -- No longer allow things like [] and (,,,) to be exported
   -- They are built in syntax, always available
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export  :: { LIE RdrName }
        :  qvar                         { L1 (IEVar (unLoc $1)) }
        |  oqtycon                      { L1 (IEThingAbs (unLoc $1)) }
        |  oqtycon '(' '..' ')'         { LL (IEThingAll (unLoc $1)) }
        |  oqtycon '(' ')'              { LL (IEThingWith (unLoc $1) []) }
        |  oqtycon '(' qcnames ')'      { LL (IEThingWith (unLoc $1) (reverse $3)) }
        |  'module' modid               { LL (IEModuleContents (unLoc $2)) }
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qcnames :: { [RdrName] }
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        :  qcnames ',' qcname_ext       { unLoc $3 : $1 }
        |  qcname_ext                   { [unLoc $1]  }
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qcname_ext :: { Located RdrName }       -- Variable or data constructor
                                        -- or tagged type constructor
        :  qcname                       { $1 }
        |  'type' qcon                  { sL (comb2 $1 $2) 
                                             (setRdrNameSpace (unLoc $2) 
                                                              tcClsName)  }
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-- Cannot pull into qcname_ext, as qcname is also used in expression.
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qcname  :: { Located RdrName }  -- Variable or data constructor
        :  qvar                         { $1 }
        |  qcon                         { $1 }
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-----------------------------------------------------------------------------
-- Import Declarations

-- import decls can be *empty*, or even just a string of semicolons
-- whereas topdecls must contain at least one topdecl.

importdecls :: { [LImportDecl RdrName] }
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        : importdecls ';' importdecl            { $3 : $1 }
        | importdecls ';'                       { $1 }
        | importdecl                            { [ $1 ] }
        | {- empty -}                           { [] }
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importdecl :: { LImportDecl RdrName }
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        : 'import' maybe_src maybe_safe optqualified maybe_pkg modid maybeas maybeimpspec 
                { L (comb4 $1 $6 $7 $8) $
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                  ImportDecl { ideclName = $6, ideclPkgQual = $5
                             , ideclSource = $2, ideclSafe = $3
                             , ideclQualified = $4, ideclImplicit = False
                             , ideclAs = unLoc $7, ideclHiding = unLoc $8 } }
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maybe_src :: { IsBootInterface }
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        : '{-# SOURCE' '#-}'                    { True }
        | {- empty -}                           { False }
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maybe_safe :: { Bool }
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        : 'safe'                                { True }
        | {- empty -}                           { False }
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maybe_pkg :: { Maybe FastString }
        : STRING                                { Just (getSTRING $1) }
        | {- empty -}                           { Nothing }

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optqualified :: { Bool }
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        : 'qualified'                           { True  }
        | {- empty -}                           { False }
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maybeas :: { Located (Maybe ModuleName) }
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        : 'as' modid                            { LL (Just (unLoc $2)) }
        | {- empty -}                           { noLoc Nothing }
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maybeimpspec :: { Located (Maybe (Bool, [LIE RdrName])) }
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        : impspec                               { L1 (Just (unLoc $1)) }
        | {- empty -}                           { noLoc Nothing }
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impspec :: { Located (Bool, [LIE RdrName]) }
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        :  '(' exportlist ')'                   { LL (False, $2) }
        |  'hiding' '(' exportlist ')'          { LL (True,  $3) }
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-----------------------------------------------------------------------------
-- Fixity Declarations

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prec    :: { Int }
        : {- empty -}           { 9 }
        | INTEGER               {% checkPrecP (L1 (fromInteger (getINTEGER $1))) }
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infix   :: { Located FixityDirection }
        : 'infix'                               { L1 InfixN  }
        | 'infixl'                              { L1 InfixL  }
        | 'infixr'                              { L1 InfixR }
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ops     :: { Located [Located RdrName] }
        : ops ',' op                            { LL ($3 : unLoc $1) }
        | op                                    { L1 [$1] }
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-----------------------------------------------------------------------------
-- Top-Level Declarations

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topdecls :: { OrdList (LHsDecl RdrName) }
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        : topdecls ';' topdecl                  { $1 `appOL` $3 }
        | topdecls ';'                          { $1 }
        | topdecl                               { $1 }
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topdecl :: { OrdList (LHsDecl RdrName) }
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        : cl_decl                               { unitOL (L1 (TyClD (unLoc $1))) }
        | ty_decl                               { unitOL (L1 (TyClD (unLoc $1))) }
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        | 'instance' inst_type where_inst
            { let (binds, sigs, ats, _) = cvBindsAndSigs (unLoc $3)
              in 
              unitOL (L (comb3 $1 $2 $3) (InstD (InstDecl $2 binds sigs ats)))}
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        | stand_alone_deriving                  { unitOL (LL (DerivD (unLoc $1))) }
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        | 'default' '(' comma_types0 ')'        { unitOL (LL $ DefD (DefaultDecl $3)) }
        | 'foreign' fdecl                       { unitOL (LL (unLoc $2)) }
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        | '{-# DEPRECATED' deprecations '#-}'   { $2 }
        | '{-# WARNING' warnings '#-}'          { $2 }
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        | '{-# RULES' rules '#-}'               { $2 }
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        | '{-# VECTORISE_SCALAR' qvar '#-}'     { unitOL $ LL $ VectD (HsVect       $2 Nothing) }
        | '{-# VECTORISE' qvar '=' exp '#-}'    { unitOL $ LL $ VectD (HsVect       $2 (Just $4)) }
        | '{-# NOVECTORISE' qvar '#-}'          { unitOL $ LL $ VectD (HsNoVect     $2) }
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        | '{-# VECTORISE' 'type' gtycon '#-}'     
                                                { unitOL $ LL $ 
                                                    VectD (HsVectTypeIn False $3 Nothing) }
        | '{-# VECTORISE_SCALAR' 'type' gtycon '#-}'     
                                                { unitOL $ LL $ 
                                                    VectD (HsVectTypeIn True $3 Nothing) }
        | '{-# VECTORISE' 'type' gtycon '=' gtycon '#-}'     
                                                { unitOL $ LL $ 
                                                    VectD (HsVectTypeIn False $3 (Just $5)) }
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        | annotation { unitOL $1 }
        | decl                                  { unLoc $1 }

        -- Template Haskell Extension
        -- The $(..) form is one possible form of infixexp
        -- but we treat an arbitrary expression just as if 
        -- it had a $(..) wrapped around it
        | infixexp                              { unitOL (LL $ mkTopSpliceDecl $1) } 
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-- Type classes
--
cl_decl :: { LTyClDecl RdrName }
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        : 'class' tycl_hdr fds where_cls        {% mkClassDecl (comb4 $1 $2 $3 $4) $2 $3 $4 }
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-- Type declarations (toplevel)
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--
ty_decl :: { LTyClDecl RdrName }
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           -- ordinary type synonyms
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        : 'type' type '=' ctypedoc
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                -- Note ctype, not sigtype, on the right of '='
                -- We allow an explicit for-all but we don't insert one
                -- in   type Foo a = (b,b)
                -- Instead we just say b is out of scope
                --
                -- Note the use of type for the head; this allows
                -- infix type constructors to be declared 
                {% mkTySynonym (comb2 $1 $4) False $2 $4 }
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           -- type family declarations
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        | 'type' 'family' type opt_kind_sig 
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                -- Note the use of type for the head; this allows
                -- infix type constructors to be declared
                {% mkTyFamily (comb3 $1 $3 $4) TypeFamily $3 (unLoc $4) }
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           -- type instance declarations
        | 'type' 'instance' type '=' ctype
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                -- Note the use of type for the head; this allows
                -- infix type constructors and type patterns
                {% mkTySynonym (comb2 $1 $5) True $3 $5 }
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          -- ordinary data type or newtype declaration
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        | data_or_newtype tycl_hdr constrs deriving
                {% mkTyData (comb4 $1 $2 $3 $4) (unLoc $1) False $2 
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                            Nothing (reverse (unLoc $3)) (unLoc $4) }
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                                   -- We need the location on tycl_hdr in case 
                                   -- constrs and deriving are both empty
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          -- ordinary GADT declaration
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        | data_or_newtype tycl_hdr opt_kind_sig 
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                 gadt_constrlist
                 deriving
                {% mkTyData (comb4 $1 $2 $4 $5) (unLoc $1) False $2 
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                            (unLoc $3) (unLoc $4) (unLoc $5) }
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                                   -- We need the location on tycl_hdr in case 
                                   -- constrs and deriving are both empty
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          -- data/newtype family
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        | 'data' 'family' type opt_kind_sig
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                {% mkTyFamily (comb3 $1 $2 $4) DataFamily $3 (unLoc $4) }
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          -- data/newtype instance declaration
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        | data_or_newtype 'instance' tycl_hdr constrs deriving
                {% mkTyData (comb4 $1 $3 $4 $5) (unLoc $1) True $3
                            Nothing (reverse (unLoc $4)) (unLoc $5) }
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          -- GADT instance declaration
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        | data_or_newtype 'instance' tycl_hdr opt_kind_sig 
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                 gadt_constrlist
                 deriving
                {% mkTyData (comb4 $1 $3 $5 $6) (unLoc $1) True $3
                            (unLoc $4) (unLoc $5) (unLoc $6) }
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-- Associated type family declarations
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--
-- * They have a different syntax than on the toplevel (no family special
--   identifier).
--
-- * They also need to be separate from instances; otherwise, data family
--   declarations without a kind signature cause parsing conflicts with empty
--   data declarations. 
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--
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at_decl_cls :: { LTyClDecl RdrName }
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           -- type family declarations
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        : 'type' type opt_kind_sig
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                -- Note the use of type for the head; this allows
                -- infix type constructors to be declared
                {% mkTyFamily (comb3 $1 $2 $3) TypeFamily $2 (unLoc $3) }
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           -- default type instance
        | 'type' type '=' ctype
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                -- Note the use of type for the head; this allows
                -- infix type constructors and type patterns
                {% mkTySynonym (comb2 $1 $4) True $2 $4 }
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          -- data/newtype family declaration
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        | 'data' type opt_kind_sig
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                {% mkTyFamily (comb3 $1 $2 $3) DataFamily $2 (unLoc $3) }
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-- Associated type instances
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--
at_decl_inst :: { LTyClDecl RdrName }
           -- type instance declarations
        : 'type' type '=' ctype
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                -- Note the use of type for the head; this allows
                -- infix type constructors and type patterns
                {% mkTySynonym (comb2 $1 $4) True $2 $4 }
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        -- data/newtype instance declaration
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        | data_or_newtype tycl_hdr constrs deriving
                {% mkTyData (comb4 $1 $2 $3 $4) (unLoc $1) True $2 
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                            Nothing (reverse (unLoc $3)) (unLoc $4) }
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        -- GADT instance declaration
        | data_or_newtype tycl_hdr opt_kind_sig 
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                 gadt_constrlist
                 deriving
                {% mkTyData (comb4 $1 $2 $4 $5) (unLoc $1) True $2 
                            (unLoc $3) (unLoc $4) (unLoc $5) }
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data_or_newtype :: { Located NewOrData }
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        : 'data'        { L1 DataType }
        | 'newtype'     { L1 NewType }
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opt_kind_sig :: { Located (Maybe Kind) }
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        :                               { noLoc Nothing }
        | '::' kind                     { LL (Just (unLoc $2)) }
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-- tycl_hdr parses the header of a class or data type decl,
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-- which takes the form
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--      T a b
--      Eq a => T a
--      (Eq a, Ord b) => T a b
--      T Int [a]                       -- for associated types
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-- Rather a lot of inlining here, else we get reduce/reduce errors
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tycl_hdr :: { Located (Maybe (LHsContext RdrName), LHsType RdrName) }
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        : context '=>' type             { LL (Just $1, $3) }
        | type                          { L1 (Nothing, $1) }
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-----------------------------------------------------------------------------
-- Stand-alone deriving

-- Glasgow extension: stand-alone deriving declarations
stand_alone_deriving :: { LDerivDecl RdrName }
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        : 'deriving' 'instance' inst_type { LL (DerivDecl $3) }
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-----------------------------------------------------------------------------
-- Nested declarations

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-- Declaration in class bodies
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--
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decl_cls  :: { Located (OrdList (LHsDecl RdrName)) }
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decl_cls  : at_decl_cls                 { LL (unitOL (L1 (TyClD (unLoc $1)))) }
          | decl                        { $1 }
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          -- A 'default' signature used with the generic-programming extension
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          | 'default' infixexp '::' sigtypedoc
                    {% do { (TypeSig l ty) <- checkValSig $2 $4
                          ; return (LL $ unitOL (LL $ SigD (GenericSig l ty))) } }

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decls_cls :: { Located (OrdList (LHsDecl RdrName)) }    -- Reversed
          : decls_cls ';' decl_cls      { LL (unLoc $1 `appOL` unLoc $3) }
          | decls_cls ';'               { LL (unLoc $1) }
          | decl_cls                    { $1 }
          | {- empty -}                 { noLoc nilOL }
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decllist_cls
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        :: { Located (OrdList (LHsDecl RdrName)) }      -- Reversed
        : '{'         decls_cls '}'     { LL (unLoc $2) }
        |     vocurly decls_cls close   { $2 }
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-- Class body
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--
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where_cls :: { Located (OrdList (LHsDecl RdrName)) }    -- Reversed
                                -- No implicit parameters
                                -- May have type declarations
        : 'where' decllist_cls          { LL (unLoc $2) }
        | {- empty -}                   { noLoc nilOL }
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-- Declarations in instance bodies
--
decl_inst  :: { Located (OrdList (LHsDecl RdrName)) }
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decl_inst  : at_decl_inst               { LL (unitOL (L1 (TyClD (unLoc $1)))) }
           | decl                       { $1 }
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decls_inst :: { Located (OrdList (LHsDecl RdrName)) }   -- Reversed
           : decls_inst ';' decl_inst   { LL (unLoc $1 `appOL` unLoc $3) }
           | decls_inst ';'             { LL (unLoc $1) }
           | decl_inst                  { $1 }
           | {- empty -}                { noLoc nilOL }
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decllist_inst 
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        :: { Located (OrdList (LHsDecl RdrName)) }      -- Reversed
        : '{'         decls_inst '}'    { LL (unLoc $2) }
        |     vocurly decls_inst close  { $2 }
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-- Instance body
--
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where_inst :: { Located (OrdList (LHsDecl RdrName)) }   -- Reversed
                                -- No implicit parameters
                                -- May have type declarations
        : 'where' decllist_inst         { LL (unLoc $2) }
        | {- empty -}                   { noLoc nilOL }
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-- Declarations in binding groups other than classes and instances
--
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decls   :: { Located (OrdList (LHsDecl RdrName)) }      
        : decls ';' decl                { let { this = unLoc $3;
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                                    rest = unLoc $1;
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                                    these = rest `appOL` this }
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                              in rest `seq` this `seq` these `seq`
                                    LL these }
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        | decls ';'                     { LL (unLoc $1) }
        | decl                          { $1 }
        | {- empty -}                   { noLoc nilOL }
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decllist :: { Located (OrdList (LHsDecl RdrName)) }
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        : '{'            decls '}'      { LL (unLoc $2) }
        |     vocurly    decls close    { $2 }
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-- Binding groups other than those of class and instance declarations
--
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binds   ::  { Located (HsLocalBinds RdrName) }          -- May have implicit parameters
                                                -- No type declarations
        : decllist                      { L1 (HsValBinds (cvBindGroup (unLoc $1))) }
        | '{'            dbinds '}'     { LL (HsIPBinds (IPBinds (unLoc $2) emptyTcEvBinds)) }
        |     vocurly    dbinds close   { L (getLoc $2) (HsIPBinds (IPBinds (unLoc $2) emptyTcEvBinds)) }
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wherebinds :: { Located (HsLocalBinds RdrName) }        -- May have implicit parameters
                                                -- No type declarations
        : 'where' binds                 { LL (unLoc $2) }
        | {- empty -}                   { noLoc emptyLocalBinds }
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-----------------------------------------------------------------------------
-- Transformation Rules

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rules   :: { OrdList (LHsDecl RdrName) }
        :  rules ';' rule                       { $1 `snocOL` $3 }
        |  rules ';'                            { $1 }
        |  rule                                 { unitOL $1 }
        |  {- empty -}                          { nilOL }
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rule    :: { LHsDecl RdrName }
        : STRING activation rule_forall infixexp '=' exp
             { LL $ RuleD (HsRule (getSTRING $1) 
                                  ($2 `orElse` AlwaysActive) 
                                  $3 $4 placeHolderNames $6 placeHolderNames) }
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activation :: { Maybe Activation } 
        : {- empty -}                           { Nothing }
        | explicit_activation                   { Just $1 }
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explicit_activation :: { Activation }  -- In brackets
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        : '[' INTEGER ']'               { ActiveAfter  (fromInteger (getINTEGER $2)) }
        | '[' '~' INTEGER ']'           { ActiveBefore (fromInteger (getINTEGER $3)) }
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rule_forall :: { [RuleBndr RdrName] }
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        : 'forall' rule_var_list '.'            { $2 }
        | {- empty -}                           { [] }
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rule_var_list :: { [RuleBndr RdrName] }
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        : rule_var                              { [$1] }
        | rule_var rule_var_list                { $1 : $2 }
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rule_var :: { RuleBndr RdrName }
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        : varid                                 { RuleBndr $1 }
        | '(' varid '::' ctype ')'              { RuleBndrSig $2 $4 }
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-----------------------------------------------------------------------------
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-- Warnings and deprecations (c.f. rules)

warnings :: { OrdList (LHsDecl RdrName) }
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        : warnings ';' warning          { $1 `appOL` $3 }
        | warnings ';'                  { $1 }
        | warning                               { $1 }
        | {- empty -}                           { nilOL }
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-- SUP: TEMPORARY HACK, not checking for `module Foo'
warning :: { OrdList (LHsDecl RdrName) }
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        : namelist strings
                { toOL [ LL $ WarningD (Warning n (WarningTxt $ unLoc $2))
                       | n <- unLoc $1 ] }
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deprecations :: { OrdList (LHsDecl RdrName) }
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        : deprecations ';' deprecation          { $1 `appOL` $3 }
        | deprecations ';'                      { $1 }
        | deprecation                           { $1 }
        | {- empty -}                           { nilOL }
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-- SUP: TEMPORARY HACK, not checking for `module Foo'
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deprecation :: { OrdList (LHsDecl RdrName) }
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        : namelist strings
                { toOL [ LL $ WarningD (Warning n (DeprecatedTxt $ unLoc $2))
                       | n <- unLoc $1 ] }
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strings :: { Located [FastString] }
    : STRING { L1 [getSTRING $1] }
    | '[' stringlist ']' { LL $ fromOL (unLoc $2) }

stringlist :: { Located (OrdList FastString) }
    : stringlist ',' STRING { LL (unLoc $1 `snocOL` getSTRING $3) }
    | STRING                { LL (unitOL (getSTRING $1)) }

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-----------------------------------------------------------------------------
-- Annotations
annotation :: { LHsDecl RdrName }
    : '{-# ANN' name_var aexp '#-}'      { LL (AnnD $ HsAnnotation (ValueAnnProvenance (unLoc $2)) $3) }
    | '{-# ANN' 'type' tycon aexp '#-}'  { LL (AnnD $ HsAnnotation (TypeAnnProvenance (unLoc $3)) $4) }
    | '{-# ANN' 'module' aexp '#-}'      { LL (AnnD $ HsAnnotation ModuleAnnProvenance $3) }

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-----------------------------------------------------------------------------
-- Foreign import and export declarations

fdecl :: { LHsDecl RdrName }
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fdecl : 'import' callconv safety fspec
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                {% mkImport $2 $3 (unLoc $4) >>= return.LL }
      | 'import' callconv        fspec          
                {% do { d <- mkImport $2 PlaySafe (unLoc $3);
                        return (LL d) } }
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      | 'export' callconv fspec
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                {% mkExport $2 (unLoc $3) >>= return.LL }
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callconv :: { CCallConv }
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          : 'stdcall'                   { StdCallConv }
          | 'ccall'                     { CCallConv   }
          | 'prim'                      { PrimCallConv}
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safety :: { Safety }
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        : 'unsafe'                      { PlayRisky }
        | 'safe'                        { PlaySafe }
        | 'interruptible'               { PlayInterruptible }
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fspec :: { Located (Located FastString, Located RdrName, LHsType RdrName) }
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       : STRING var '::' sigtypedoc     { LL (L (getLoc $1) (getSTRING $1), $2, $4) }
       |        var '::' sigtypedoc     { LL (noLoc nilFS, $1, $3) }
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         -- if the entity string is missing, it defaults to the empty string;
         -- the meaning of an empty entity string depends on the calling
         -- convention

-----------------------------------------------------------------------------
-- Type signatures

opt_sig :: { Maybe (LHsType RdrName) }
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        : {- empty -}                   { Nothing }
        | '::' sigtype                  { Just $2 }
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opt_asig :: { Maybe (LHsType RdrName) }
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        : {- empty -}                   { Nothing }
        | '::' atype                    { Just $2 }
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sigtype :: { LHsType RdrName }          -- Always a HsForAllTy,
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                                        -- to tell the renamer where to generalise
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        : ctype                         { L1 (mkImplicitHsForAllTy (noLoc []) $1) }
        -- Wrap an Implicit forall if there isn't one there already
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sigtypedoc :: { LHsType RdrName }       -- Always a HsForAllTy
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        : ctypedoc                      { L1 (mkImplicitHsForAllTy (noLoc []) $1) }
        -- Wrap an Implicit forall if there isn't one there already
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sig_vars :: { Located [Located RdrName] }
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         : sig_vars ',' var             { LL ($3 : unLoc $1) }
         | var                          { L1 [$1] }
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sigtypes1 :: { [LHsType RdrName] }      -- Always HsForAllTys
        : sigtype                       { [ $1 ] }
        | sigtype ',' sigtypes1         { $1 : $3 }
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-----------------------------------------------------------------------------
-- Types

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infixtype :: { LHsType RdrName }
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        : btype qtyconop type         { LL $ HsOpTy $1 $2 $3 }
        | btype tyvarop  type    { LL $ HsOpTy $1 $2 $3 }
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strict_mark :: { Located HsBang }
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        : '!'                           { L1 HsStrict }
        | '{-# UNPACK' '#-}' '!'        { LL HsUnpack }
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-- A ctype is a for-all type
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ctype   :: { LHsType RdrName }
        : 'forall' tv_bndrs '.' ctype   { LL $ mkExplicitHsForAllTy $2 (noLoc []) $4 }
        | context '=>' ctype            { LL $ mkImplicitHsForAllTy   $1 $3 }
        -- A type of form (context => type) is an *implicit* HsForAllTy
        | ipvar '::' type               { LL (HsIParamTy (unLoc $1) $3) }
        | type                          { $1 }
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----------------------
-- Notes for 'ctypedoc'
-- It would have been nice to simplify the grammar by unifying `ctype` and 
-- ctypedoc` into one production, allowing comments on types everywhere (and
-- rejecting them after parsing, where necessary).  This is however not possible
-- since it leads to ambiguity. The reason is the support for comments on record
-- fields: 
--         data R = R { field :: Int -- ^ comment on the field }
-- If we allow comments on types here, it's not clear if the comment applies
-- to 'field' or to 'Int'. So we must use `ctype` to describe the type.

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ctypedoc :: { LHsType RdrName }
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        : 'forall' tv_bndrs '.' ctypedoc        { LL $ mkExplicitHsForAllTy $2 (noLoc []) $4 }
        | context '=>' ctypedoc         { LL $ mkImplicitHsForAllTy   $1 $3 }
        -- A type of form (context => type) is an *implicit* HsForAllTy
        | ipvar '::' type               { LL (HsIParamTy (unLoc $1) $3) }
        | typedoc                       { $1 }
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----------------------
-- Notes for 'context'
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-- We parse a context as a btype so that we don't get reduce/reduce
-- errors in ctype.  The basic problem is that
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--      (Eq a, Ord a)
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-- looks so much like a tuple type.  We can't tell until we find the =>
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-- We have the t1 ~ t2 form both in 'context' and in type, 
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-- to permit an individual equational constraint without parenthesis.
-- Thus for some reason we allow    f :: a~b => blah
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-- but not                          f :: ?x::Int => blah
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context :: { LHsContext RdrName }
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        : btype '~'      btype          {% checkContext
                                             (LL $ HsEqTy $1 $3) }
        | btype                         {% checkContext $1 }
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type :: { LHsType RdrName }
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        : btype                         { $1 }
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        | btype qtyconop type           { LL $ HsOpTy $1 $2 $3 }
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        | btype tyvarop  type           { LL $ HsOpTy $1 $2 $3 }
        | btype '->'     ctype          { LL $ HsFunTy $1 $3 }
        | btype '~'      btype          { LL $ HsEqTy $1 $3 }
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typedoc :: { LHsType RdrName }
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        : btype                          { $1 }
        | btype docprev                  { LL $ HsDocTy $1 $2 }
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        | btype qtyconop type            { LL $ HsOpTy $1 $2 $3 }
        | btype qtyconop type docprev    { LL $ HsDocTy (L (comb3 $1 $2 $3) (HsOpTy $1 $2 $3)) $4 }
        | btype tyvarop  type            { LL $ HsOpTy $1 $2 $3 }
        | btype tyvarop  type docprev    { LL $ HsDocTy (L (comb3 $1 $2 $3) (HsOpTy $1 $2 $3)) $4 }
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        | btype '->'     ctypedoc        { LL $ HsFunTy $1 $3 }
        | btype docprev '->' ctypedoc    { LL $ HsFunTy (L (comb2 $1 $2) (HsDocTy $1 $2)) $4 }
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        | btype '~'      btype           { LL $ HsEqTy $1 $3 }
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btype :: { LHsType RdrName }
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        : btype atype                   { LL $ HsAppTy $1 $2 }
        | atype                         { $1 }
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atype :: { LHsType RdrName }
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        : gtycon                        { L1 (HsTyVar (unLoc $1)) }
        | tyvar                         { L1 (HsTyVar (unLoc $1)) }
        | strict_mark atype             { LL (HsBangTy (unLoc $1) $2) }  -- Constructor sigs only
        | '{' fielddecls '}'            {% checkRecordSyntax (LL $ HsRecTy $2) } -- Constructor sigs only
        | '(' ctype ',' comma_types1 ')'  { LL $ HsTupleTy (HsBoxyTuple placeHolderKind)  ($2:$4) }
        | '(#' comma_types1 '#)'        { LL $ HsTupleTy HsUnboxedTuple $2     }
        | '[' ctype ']'                 { LL $ HsListTy  $2 }
        | '[:' ctype ':]'               { LL $ HsPArrTy  $2 }
        | '(' ctype ')'                 { LL $ HsParTy   $2 }
        | '(' ctype '::' kind ')'       { LL $ HsKindSig $2 (unLoc $4) }
        | quasiquote                    { L1 (HsQuasiQuoteTy (unLoc $1)) }
        | '$(' exp ')'                  { LL $ mkHsSpliceTy $2 }
        | TH_ID_SPLICE                  { LL $ mkHsSpliceTy $ L1 $ HsVar $ 
                                          mkUnqual varName (getTH_ID_SPLICE $1) }
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-- An inst_type is what occurs in the head of an instance decl
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--      e.g.  (Foo a, Gaz b) => Wibble a b
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-- It's kept as a single type, with a MonoDictTy at the right
-- hand corner, for convenience.
inst_type :: { LHsType RdrName }
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        : sigtype                       { $1 }
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inst_types1 :: { [LHsType RdrName] }
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        : inst_type                     { [$1] }
        | inst_type ',' inst_types1     { $1 : $3 }
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comma_types0  :: { [LHsType RdrName] }
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        : comma_types1                  { $1 }
        | {- empty -}                   { [] }
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comma_types1    :: { [LHsType RdrName] }
        : ctype                         { [$1] }
        | ctype  ',' comma_types1       { $1 : $3 }
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tv_bndrs :: { [LHsTyVarBndr RdrName] }
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         : tv_bndr tv_bndrs             { $1 : $2 }
         | {- empty -}                  { [] }
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tv_bndr :: { LHsTyVarBndr RdrName }
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        : tyvar                         { L1 (UserTyVar (unLoc $1) placeHolderKind) }
        | '(' tyvar '::' kind ')'       { LL (KindedTyVar (unLoc $2) 
                                                          (unLoc $4)) }
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fds :: { Located [Located (FunDep RdrName)] }
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        : {- empty -}                   { noLoc [] }
        | '|' fds1                      { LL (reverse (unLoc $2)) }
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fds1 :: { Located [Located (FunDep RdrName)] }
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        : fds1 ',' fd                   { LL ($3 : unLoc $1) }
        | fd                            { L1 [$1] }
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fd :: { Located (FunDep RdrName) }
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        : varids0 '->' varids0          { L (comb3 $1 $2 $3)
                                           (reverse (unLoc $1), reverse (unLoc $3)) }
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varids0 :: { Located [RdrName] }
        : {- empty -}                   { noLoc [] }
        | varids0 tyvar                 { LL (unLoc $2 : unLoc $1) }
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-----------------------------------------------------------------------------
-- Kinds

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kind    :: { Located Kind }
        : akind                 { $1 }
        | akind '->' kind       { LL (mkArrowKind (unLoc $1) (unLoc $3)) }
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akind   :: { Located Kind }
        : '*'                   { L1 liftedTypeKind }
        | '!'                   { L1 unliftedTypeKind }
        | CONID                 {% checkKindName (L1 (getCONID $1)) }
        | '(' kind ')'          { LL (unLoc $2) }
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-----------------------------------------------------------------------------
-- Datatype declarations

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gadt_constrlist :: { Located [LConDecl RdrName] }       -- Returned in order
        : 'where' '{'        gadt_constrs '}'      { L (comb2 $1 $3) (unLoc $3) }
        | 'where' vocurly    gadt_constrs close    { L (comb2 $1 $3) (unLoc $3) }
        | {- empty -}                              { noLoc [] }
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gadt_constrs :: { Located [LConDecl RdrName] }
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        : gadt_constr ';' gadt_constrs  { L (comb2 (head $1) $3) ($1 ++ unLoc $3) }
        | gadt_constr                   { L (getLoc (head $1)) $1 }
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        | {- empty -}                   { noLoc [] }
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-- We allow the following forms:
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--      C :: Eq a => a -> T a
--      C :: forall a. Eq a => !a -> T a
--      D { x,y :: a } :: T a
--      forall a. Eq a => D { x,y :: a } :: T a
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