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-----------------------------------------------------------------------------
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-- (c) The University of Glasgow, 2006
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--
-- GHC's lexer.
--
-- This is a combination of an Alex-generated lexer from a regex
-- definition, with some hand-coded bits.
--
-- Completely accurate information about token-spans within the source
-- file is maintained.  Every token has a start and end SrcLoc attached to it.
--
-----------------------------------------------------------------------------

--   ToDo / known bugs:
--    - Unicode
--    - parsing integers is a bit slow
--    - readRational is a bit slow
--
--   Known bugs, that were also in the previous version:
--    - M... should be 3 tokens, not 1.
--    - pragma-end should be only valid in a pragma

{
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{-# OPTIONS -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
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--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
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-- for details

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module Lexer (
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   Token(..), lexer, pragState, mkPState, PState(..),
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   P(..), ParseResult(..), getSrcLoc, 
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   failLocMsgP, failSpanMsgP, srcParseFail,
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   getMessages,
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   popContext, pushCurrentContext, setLastToken, setSrcLoc,
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   getLexState, popLexState, pushLexState,
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   extension, standaloneDerivingEnabled, bangPatEnabled,
   addWarning
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  ) where

#include "HsVersions.h"

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import Bag
import ErrUtils
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import Outputable
import StringBuffer
import FastString
import FastTypes
import SrcLoc
import UniqFM
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import DynFlags
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import Ctype
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import Util		( maybePrefixMatch, readRational )
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import Control.Monad
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import Data.Bits
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import Data.Char 	( chr, isSpace )
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import Data.Ratio
import Debug.Trace
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#if __GLASGOW_HASKELL__ >= 605
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import Data.Char 	( GeneralCategory(..), generalCategory, isPrint, isUpper )
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#else
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import Compat.Unicode	( GeneralCategory(..), generalCategory, isPrint, isUpper )
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#endif
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}

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$unispace    = \x05 -- Trick Alex into handling Unicode. See alexGetChar.
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$whitechar   = [\ \n\r\f\v\xa0 $unispace]
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$white_no_nl = $whitechar # \n
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$tab         = \t
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$ascdigit  = 0-9
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$unidigit  = \x03 -- Trick Alex into handling Unicode. See alexGetChar.
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$decdigit  = $ascdigit -- for now, should really be $digit (ToDo)
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$digit     = [$ascdigit $unidigit]

$special   = [\(\)\,\;\[\]\`\{\}]
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$ascsymbol = [\!\#\$\%\&\*\+\.\/\<\=\>\?\@\\\^\|\-\~ \xa1-\xbf \xd7 \xf7]
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$unisymbol = \x04 -- Trick Alex into handling Unicode. See alexGetChar.
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$symbol    = [$ascsymbol $unisymbol] # [$special \_\:\"\']

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$unilarge  = \x01 -- Trick Alex into handling Unicode. See alexGetChar.
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$asclarge  = [A-Z \xc0-\xd6 \xd8-\xde]
$large     = [$asclarge $unilarge]

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$unismall  = \x02 -- Trick Alex into handling Unicode. See alexGetChar.
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$ascsmall  = [a-z \xdf-\xf6 \xf8-\xff]
$small     = [$ascsmall $unismall \_]

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$unigraphic = \x06 -- Trick Alex into handling Unicode. See alexGetChar.
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$graphic   = [$small $large $symbol $digit $special $unigraphic \:\"\']
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$octit	   = 0-7
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$hexit     = [$decdigit A-F a-f]
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$symchar   = [$symbol \:]
$nl        = [\n\r]
$idchar    = [$small $large $digit \']

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$docsym    = [\| \^ \* \$]

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@varid     = $small $idchar*
@conid     = $large $idchar*

@varsym    = $symbol $symchar*
@consym    = \: $symchar*

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@decimal     = $decdigit+
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@octal       = $octit+
@hexadecimal = $hexit+
@exponent    = [eE] [\-\+]? @decimal

-- we support the hierarchical module name extension:
@qual = (@conid \.)+

@floating_point = @decimal \. @decimal @exponent? | @decimal @exponent

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-- normal signed numerical literals can only be explicitly negative,
-- not explicitly positive (contrast @exponent)
@negative = \-
@signed = @negative ?

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haskell :-

-- everywhere: skip whitespace and comments
$white_no_nl+ 				;
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$tab+         { warn Opt_WarnTabs (text "Tab character") }
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-- Everywhere: deal with nested comments.  We explicitly rule out
-- pragmas, "{-#", so that we don't accidentally treat them as comments.
-- (this can happen even though pragmas will normally take precedence due to
-- longest-match, because pragmas aren't valid in every state, but comments
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-- are). We also rule out nested Haddock comments, if the -haddock flag is
-- set.

"{-" / { isNormalComment } { nested_comment lexToken }
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-- Single-line comments are a bit tricky.  Haskell 98 says that two or
-- more dashes followed by a symbol should be parsed as a varsym, so we
-- have to exclude those.
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-- Since Haddock comments aren't valid in every state, we need to rule them
-- out here.  

-- The following two rules match comments that begin with two dashes, but
-- continue with a different character. The rules test that this character
-- is not a symbol (in which case we'd have a varsym), and that it's not a
-- space followed by a Haddock comment symbol (docsym) (in which case we'd
-- have a Haddock comment). The rules then munch the rest of the line.

"-- " ~$docsym .* ;
"--" [^$symbol : \ ] .* ;

-- Next, match Haddock comments if no -haddock flag

"-- " $docsym .* / { ifExtension (not . haddockEnabled) } ;

-- Now, when we've matched comments that begin with 2 dashes and continue
-- with a different character, we need to match comments that begin with three
-- or more dashes (which clearly can't be Haddock comments). We only need to
-- make sure that the first non-dash character isn't a symbol, and munch the
-- rest of the line.

"---"\-* [^$symbol :] .* ;

-- Since the previous rules all match dashes followed by at least one
-- character, we also need to match a whole line filled with just dashes.

"--"\-* / { atEOL } ;

-- We need this rule since none of the other single line comment rules
-- actually match this case.

"-- " / { atEOL } ;
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-- 'bol' state: beginning of a line.  Slurp up all the whitespace (including
-- blank lines) until we find a non-whitespace character, then do layout
-- processing.
--
-- One slight wibble here: what if the line begins with {-#? In
-- theory, we have to lex the pragma to see if it's one we recognise,
-- and if it is, then we backtrack and do_bol, otherwise we treat it
-- as a nested comment.  We don't bother with this: if the line begins
-- with {-#, then we'll assume it's a pragma we know about and go for do_bol.
<bol> {
  \n					;
  ^\# (line)?				{ begin line_prag1 }
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  ^\# pragma .* \n			; -- GCC 3.3 CPP generated, apparently
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  ^\# \! .* \n				; -- #!, for scripts
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  ()					{ do_bol }
}

-- after a layout keyword (let, where, do, of), we begin a new layout
-- context if the curly brace is missing.
-- Careful! This stuff is quite delicate.
<layout, layout_do> {
  \{ / { notFollowedBy '-' }		{ pop_and open_brace }
	-- we might encounter {-# here, but {- has been handled already
  \n					;
  ^\# (line)?				{ begin line_prag1 }
}

-- do is treated in a subtly different way, see new_layout_context
<layout>    ()				{ new_layout_context True }
<layout_do> ()				{ new_layout_context False }

-- after a new layout context which was found to be to the left of the
-- previous context, we have generated a '{' token, and we now need to
-- generate a matching '}' token.
<layout_left>  ()			{ do_layout_left }

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<0,option_prags> \n				{ begin bol }
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"{-#" $whitechar* (line|LINE) 		{ begin line_prag2 }

-- single-line line pragmas, of the form
--    # <line> "<file>" <extra-stuff> \n
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<line_prag1> $decdigit+			{ setLine line_prag1a }
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<line_prag1a> \" [$graphic \ ]* \"	{ setFile line_prag1b }
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<line_prag1b> .*			{ pop }

-- Haskell-style line pragmas, of the form
--    {-# LINE <line> "<file>" #-}
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<line_prag2> $decdigit+			{ setLine line_prag2a }
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<line_prag2a> \" [$graphic \ ]* \"	{ setFile line_prag2b }
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<line_prag2b> "#-}"|"-}"		{ pop }
   -- NOTE: accept -} at the end of a LINE pragma, for compatibility
   -- with older versions of GHC which generated these.
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-- We only want RULES pragmas to be picked up when explicit forall
-- syntax is enabled is on, because the contents of the pragma always
-- uses it. If it's not on then we're sure to get a parse error.
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-- (ToDo: we should really emit a warning when ignoring pragmas)
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-- XXX Now that we can enable this without the -fglasgow-exts hammer,
-- is it better just to let the parse error happen?
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<0>
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  "{-#" $whitechar* (RULES|rules) / { ifExtension explicitForallEnabled } { token ITrules_prag }
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<0,option_prags> {
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  "{-#" $whitechar* (INLINE|inline)	{ token (ITinline_prag True) }
  "{-#" $whitechar* (NO(T?)INLINE|no(t?)inline)
  					{ token (ITinline_prag False) }
  "{-#" $whitechar* (SPECIALI[SZ]E|speciali[sz]e)
  					{ token ITspec_prag }
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  "{-#" $whitechar* (SPECIALI[SZ]E|speciali[sz]e)
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	$whitechar* (INLINE|inline)	{ token (ITspec_inline_prag True) }
  "{-#" $whitechar* (SPECIALI[SZ]E|speciali[sz]e)
	$whitechar* (NO(T?)INLINE|no(t?)inline)
					{ token (ITspec_inline_prag False) }
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  "{-#" $whitechar* (SOURCE|source)	{ token ITsource_prag }
  "{-#" $whitechar* (DEPRECATED|deprecated)
  					{ token ITdeprecated_prag }
  "{-#" $whitechar* (SCC|scc)		{ token ITscc_prag }
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  "{-#" $whitechar* (GENERATED|generated)
  					{ token ITgenerated_prag }
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  "{-#" $whitechar* (CORE|core)		{ token ITcore_prag }
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  "{-#" $whitechar* (UNPACK|unpack)	{ token ITunpack_prag }
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  "{-#" $whitechar* (DOC_OPTIONS|doc_options)
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  / { ifExtension haddockEnabled }     { lex_string_prag ITdocOptions }

 "{-#"                                 { nested_comment lexToken }
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  -- ToDo: should only be valid inside a pragma:
  "#-}" 				{ token ITclose_prag}
}

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<option_prags> {
  "{-#" $whitechar* (OPTIONS|options)   { lex_string_prag IToptions_prag }
  "{-#" $whitechar* (OPTIONS_GHC|options_ghc)
                                        { lex_string_prag IToptions_prag }
  "{-#" $whitechar* (LANGUAGE|language) { token ITlanguage_prag }
  "{-#" $whitechar* (INCLUDE|include)   { lex_string_prag ITinclude_prag }
}
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<0,option_prags> {
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	-- This is to catch things like {-# OPTIONS OPTIONS_HUGS ... 
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  "{-#" $whitechar* $idchar+		{ nested_comment lexToken }
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}

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-- '0' state: ordinary lexemes

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-- Haddock comments

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<0> {
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  "-- " $docsym    / { ifExtension haddockEnabled } { multiline_doc_comment }
  "{-" \ ? $docsym / { ifExtension haddockEnabled } { nested_doc_comment }
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}

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-- "special" symbols

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<0> {
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  "[:" / { ifExtension parrEnabled }	{ token ITopabrack }
  ":]" / { ifExtension parrEnabled }	{ token ITcpabrack }
}
  
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<0> {
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  "[|"	    / { ifExtension thEnabled }	{ token ITopenExpQuote }
  "[e|"	    / { ifExtension thEnabled }	{ token ITopenExpQuote }
  "[p|"	    / { ifExtension thEnabled }	{ token ITopenPatQuote }
  "[d|"	    / { ifExtension thEnabled }	{ layout_token ITopenDecQuote }
  "[t|"	    / { ifExtension thEnabled }	{ token ITopenTypQuote }
  "|]"	    / { ifExtension thEnabled }	{ token ITcloseQuote }
  \$ @varid / { ifExtension thEnabled }	{ skip_one_varid ITidEscape }
  "$("	    / { ifExtension thEnabled }	{ token ITparenEscape }
}

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<0> {
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  "(|" / { ifExtension arrowsEnabled `alexAndPred` notFollowedBySymbol }
					{ special IToparenbar }
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  "|)" / { ifExtension arrowsEnabled }  { special ITcparenbar }
}

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<0> {
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  \? @varid / { ifExtension ipEnabled }	{ skip_one_varid ITdupipvarid }
}

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<0> {
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  "(#" / { ifExtension unboxedTuplesEnabled `alexAndPred` notFollowedBySymbol }
         { token IToubxparen }
  "#)" / { ifExtension unboxedTuplesEnabled }
         { token ITcubxparen }
}

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<0> {
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  "{|" / { ifExtension genericsEnabled } { token ITocurlybar }
  "|}" / { ifExtension genericsEnabled } { token ITccurlybar }
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}

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<0,option_prags> {
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  \(					{ special IToparen }
  \)					{ special ITcparen }
  \[					{ special ITobrack }
  \]					{ special ITcbrack }
  \,					{ special ITcomma }
  \;					{ special ITsemi }
  \`					{ special ITbackquote }
 				
  \{					{ open_brace }
  \}					{ close_brace }
}

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<0,option_prags> {
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  @qual @varid			{ idtoken qvarid }
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  @qual @conid			{ idtoken qconid }
  @varid			{ varid }
  @conid			{ idtoken conid }
}

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<0> {
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  @qual @varid "#"+ / { ifExtension magicHashEnabled } { idtoken qvarid }
  @qual @conid "#"+ / { ifExtension magicHashEnabled } { idtoken qconid }
  @varid "#"+       / { ifExtension magicHashEnabled } { varid }
  @conid "#"+       / { ifExtension magicHashEnabled } { idtoken conid }
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}

-- ToDo: M.(,,,)

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<0> {
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  @qual @varsym			{ idtoken qvarsym }
  @qual @consym			{ idtoken qconsym }
  @varsym			{ varsym }
  @consym			{ consym }
}

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-- For the normal boxed literals we need to be careful
-- when trying to be close to Haskell98
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<0> {
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  -- Normal integral literals (:: Num a => a, from Integer)
  @decimal			{ tok_num positive 0 0 decimal }
  0[oO] @octal			{ tok_num positive 2 2 octal }
  0[xX] @hexadecimal		{ tok_num positive 2 2 hexadecimal }

  -- Normal rational literals (:: Fractional a => a, from Rational)
  @floating_point		{ strtoken tok_float }
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}

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<0> {
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  -- Unboxed ints (:: Int#)
  -- It's simpler (and faster?) to give separate cases to the negatives,
  -- especially considering octal/hexadecimal prefixes.
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  @decimal \# / { ifExtension magicHashEnabled } { tok_primint positive 0 1 decimal }
  0[oO] @octal \# / { ifExtension magicHashEnabled } { tok_primint positive 2 3 octal }
  0[xX] @hexadecimal \# / { ifExtension magicHashEnabled } { tok_primint positive 2 3 hexadecimal }
  @negative @decimal \# / { ifExtension magicHashEnabled } { tok_primint negative 1 2 decimal }
  @negative 0[oO] @octal \# / { ifExtension magicHashEnabled } { tok_primint negative 3 4 octal }
  @negative 0[xX] @hexadecimal \# / { ifExtension magicHashEnabled } { tok_primint negative 3 4 hexadecimal }
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  -- Unboxed floats and doubles (:: Float#, :: Double#)
  -- prim_{float,double} work with signed literals
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  @signed @floating_point \# / { ifExtension magicHashEnabled } { init_strtoken 1 tok_primfloat }
  @signed @floating_point \# \# / { ifExtension magicHashEnabled } { init_strtoken 2 tok_primdouble }
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}

-- Strings and chars are lexed by hand-written code.  The reason is
-- that even if we recognise the string or char here in the regex
-- lexer, we would still have to parse the string afterward in order
-- to convert it to a String.
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<0> {
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  \'				{ lex_char_tok }
  \" 				{ lex_string_tok }
}

{
-- -----------------------------------------------------------------------------
-- The token type

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data Token
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  = ITas  			-- Haskell keywords
  | ITcase
  | ITclass
  | ITdata
  | ITdefault
  | ITderiving
  | ITdo
  | ITelse
  | IThiding
  | ITif
  | ITimport
  | ITin
  | ITinfix
  | ITinfixl
  | ITinfixr
  | ITinstance
  | ITlet
  | ITmodule
  | ITnewtype
  | ITof
  | ITqualified
  | ITthen
  | ITtype
  | ITwhere
  | ITscc			-- ToDo: remove (we use {-# SCC "..." #-} now)

  | ITforall			-- GHC extension keywords
  | ITforeign
  | ITexport
  | ITlabel
  | ITdynamic
  | ITsafe
  | ITthreadsafe
  | ITunsafe
  | ITstdcallconv
  | ITccallconv
  | ITdotnet
  | ITmdo
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  | ITfamily
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	-- Pragmas
  | ITinline_prag Bool		-- True <=> INLINE, False <=> NOINLINE
  | ITspec_prag			-- SPECIALISE	
  | ITspec_inline_prag Bool	-- SPECIALISE INLINE (or NOINLINE)
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  | ITsource_prag
  | ITrules_prag
  | ITdeprecated_prag
  | ITline_prag
  | ITscc_prag
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  | ITgenerated_prag
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  | ITcore_prag                 -- hdaume: core annotations
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  | ITunpack_prag
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  | ITclose_prag
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  | IToptions_prag String
  | ITinclude_prag String
  | ITlanguage_prag
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  | ITdotdot  			-- reserved symbols
  | ITcolon
  | ITdcolon
  | ITequal
  | ITlam
  | ITvbar
  | ITlarrow
  | ITrarrow
  | ITat
  | ITtilde
  | ITdarrow
  | ITminus
  | ITbang
  | ITstar
  | ITdot

  | ITbiglam			-- GHC-extension symbols

  | ITocurly  			-- special symbols
  | ITccurly
  | ITocurlybar                 -- {|, for type applications
  | ITccurlybar                 -- |}, for type applications
  | ITvocurly
  | ITvccurly
  | ITobrack
  | ITopabrack			-- [:, for parallel arrays with -fparr
  | ITcpabrack			-- :], for parallel arrays with -fparr
  | ITcbrack
  | IToparen
  | ITcparen
  | IToubxparen
  | ITcubxparen
  | ITsemi
  | ITcomma
  | ITunderscore
  | ITbackquote

  | ITvarid   FastString	-- identifiers
  | ITconid   FastString
  | ITvarsym  FastString
  | ITconsym  FastString
  | ITqvarid  (FastString,FastString)
  | ITqconid  (FastString,FastString)
  | ITqvarsym (FastString,FastString)
  | ITqconsym (FastString,FastString)

  | ITdupipvarid   FastString	-- GHC extension: implicit param: ?x

  | ITpragma StringBuffer

  | ITchar       Char
  | ITstring     FastString
  | ITinteger    Integer
  | ITrational   Rational

  | ITprimchar   Char
  | ITprimstring FastString
  | ITprimint    Integer
  | ITprimfloat  Rational
  | ITprimdouble Rational

  -- MetaHaskell extension tokens
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  | ITopenExpQuote  		--  [| or [e|
  | ITopenPatQuote		--  [p|
  | ITopenDecQuote		--  [d|
  | ITopenTypQuote		--  [t|         
  | ITcloseQuote		--  |]
  | ITidEscape   FastString	--  $x
  | ITparenEscape		--  $( 
  | ITvarQuote			--  '
  | ITtyQuote			--  ''
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  -- Arrow notation extension
  | ITproc
  | ITrec
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  | IToparenbar			--  (|
  | ITcparenbar			--  |)
  | ITlarrowtail		--  -<
  | ITrarrowtail		--  >-
  | ITLarrowtail		--  -<<
  | ITRarrowtail		--  >>-
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  | ITunknown String		-- Used when the lexer can't make sense of it
  | ITeof			-- end of file token
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  -- Documentation annotations
  | ITdocCommentNext  String     -- something beginning '-- |'
  | ITdocCommentPrev  String     -- something beginning '-- ^'
  | ITdocCommentNamed String     -- something beginning '-- $'
  | ITdocSection      Int String -- a section heading
  | ITdocOptions      String     -- doc options (prune, ignore-exports, etc)

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#ifdef DEBUG
  deriving Show -- debugging
#endif

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isSpecial :: Token -> Bool
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-- If we see M.x, where x is a keyword, but
-- is special, we treat is as just plain M.x, 
-- not as a keyword.
isSpecial ITas        	= True
isSpecial IThiding    	= True
isSpecial ITqualified 	= True
isSpecial ITforall    	= True
isSpecial ITexport    	= True
isSpecial ITlabel     	= True
isSpecial ITdynamic   	= True
isSpecial ITsafe    	= True
isSpecial ITthreadsafe 	= True
isSpecial ITunsafe    	= True
isSpecial ITccallconv   = True
isSpecial ITstdcallconv = True
isSpecial ITmdo		= True
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isSpecial ITfamily	= True
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isSpecial _             = False

-- the bitmap provided as the third component indicates whether the
-- corresponding extension keyword is valid under the extension options
-- provided to the compiler; if the extension corresponding to *any* of the
-- bits set in the bitmap is enabled, the keyword is valid (this setup
-- facilitates using a keyword in two different extensions that can be
-- activated independently)
--
reservedWordsFM = listToUFM $
	map (\(x, y, z) -> (mkFastString x, (y, z)))
       [( "_",		ITunderscore, 	0 ),
	( "as",		ITas, 		0 ),
	( "case",	ITcase, 	0 ),     
	( "class",	ITclass, 	0 ),    
	( "data",	ITdata, 	0 ),     
	( "default",	ITdefault, 	0 ),  
	( "deriving",	ITderiving, 	0 ), 
	( "do",		ITdo, 		0 ),       
	( "else",	ITelse, 	0 ),     
	( "hiding",	IThiding, 	0 ),
	( "if",		ITif, 		0 ),       
	( "import",	ITimport, 	0 ),   
	( "in",		ITin, 		0 ),       
	( "infix",	ITinfix, 	0 ),    
	( "infixl",	ITinfixl, 	0 ),   
	( "infixr",	ITinfixr, 	0 ),   
	( "instance",	ITinstance, 	0 ), 
	( "let",	ITlet, 		0 ),      
	( "module",	ITmodule, 	0 ),   
	( "newtype",	ITnewtype, 	0 ),  
	( "of",		ITof, 		0 ),       
	( "qualified",	ITqualified, 	0 ),
	( "then",	ITthen, 	0 ),     
	( "type",	ITtype, 	0 ),     
	( "where",	ITwhere, 	0 ),
	( "_scc_",	ITscc, 		0 ),		-- ToDo: remove

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      	( "forall",	ITforall,	 bit explicitForallBit),
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	( "mdo",	ITmdo,		 bit recursiveDoBit),
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	( "family",	ITfamily,	 bit tyFamBit),
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	( "foreign",	ITforeign,	 bit ffiBit),
	( "export",	ITexport,	 bit ffiBit),
	( "label",	ITlabel,	 bit ffiBit),
	( "dynamic",	ITdynamic,	 bit ffiBit),
	( "safe",	ITsafe,		 bit ffiBit),
	( "threadsafe",	ITthreadsafe,	 bit ffiBit),
	( "unsafe",	ITunsafe,	 bit ffiBit),
	( "stdcall",    ITstdcallconv,	 bit ffiBit),
	( "ccall",      ITccallconv,	 bit ffiBit),
	( "dotnet",     ITdotnet,	 bit ffiBit),

	( "rec",	ITrec,		 bit arrowsBit),
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	( "proc",	ITproc,		 bit arrowsBit)
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     ]

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reservedSymsFM :: UniqFM (Token, Int -> Bool)
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reservedSymsFM = listToUFM $
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    map (\ (x,y,z) -> (mkFastString x,(y,z)))
      [ ("..",  ITdotdot,   always)
        -- (:) is a reserved op, meaning only list cons
       ,(":",   ITcolon,    always)
       ,("::",  ITdcolon,   always)
       ,("=",   ITequal,    always)
       ,("\\",  ITlam,      always)
       ,("|",   ITvbar,     always)
       ,("<-",  ITlarrow,   always)
       ,("->",  ITrarrow,   always)
       ,("@",   ITat,       always)
       ,("~",   ITtilde,    always)
       ,("=>",  ITdarrow,   always)
       ,("-",   ITminus,    always)
       ,("!",   ITbang,     always)

        -- For data T (a::*) = MkT
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       ,("*", ITstar, \i -> kindSigsEnabled i || tyFamEnabled i)
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        -- For 'forall a . t'
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       ,(".", ITdot, explicitForallEnabled)
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       ,("-<",  ITlarrowtail, arrowsEnabled)
       ,(">-",  ITrarrowtail, arrowsEnabled)
       ,("-<<", ITLarrowtail, arrowsEnabled)
       ,(">>-", ITRarrowtail, arrowsEnabled)
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#if __GLASGOW_HASKELL__ >= 605
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       ,("∷",   ITdcolon, unicodeSyntaxEnabled)
       ,("⇒",   ITdarrow, unicodeSyntaxEnabled)
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       ,("∀",   ITforall, \i -> unicodeSyntaxEnabled i &&
                                explicitForallEnabled i)
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       ,("→",   ITrarrow, unicodeSyntaxEnabled)
       ,("←",   ITlarrow, unicodeSyntaxEnabled)
       ,("⋯",   ITdotdot, unicodeSyntaxEnabled)
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        -- ToDo: ideally, → and ∷ should be "specials", so that they cannot
        -- form part of a large operator.  This would let us have a better
        -- syntax for kinds: ɑ∷*→* would be a legal kind signature. (maybe).
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#endif
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       ]

-- -----------------------------------------------------------------------------
-- Lexer actions

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type Action = SrcSpan -> StringBuffer -> Int -> P (Located Token)
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special :: Token -> Action
special tok span _buf len = return (L span tok)
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token, layout_token :: Token -> Action
token t span buf len = return (L span t)
layout_token t span buf len = pushLexState layout >> return (L span t)
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idtoken :: (StringBuffer -> Int -> Token) -> Action
idtoken f span buf len = return (L span $! (f buf len))
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skip_one_varid :: (FastString -> Token) -> Action
skip_one_varid f span buf len 
  = return (L span $! f (lexemeToFastString (stepOn buf) (len-1)))
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strtoken :: (String -> Token) -> Action
strtoken f span buf len = 
  return (L span $! (f $! lexemeToString buf len))
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init_strtoken :: Int -> (String -> Token) -> Action
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-- like strtoken, but drops the last N character(s)
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init_strtoken drop f span buf len = 
  return (L span $! (f $! lexemeToString buf (len-drop)))
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begin :: Int -> Action
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begin code _span _str _len = do pushLexState code; lexToken
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pop :: Action
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pop _span _buf _len = do popLexState; lexToken
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pop_and :: Action -> Action
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pop_and act span buf len = do popLexState; act span buf len
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{-# INLINE nextCharIs #-}
nextCharIs buf p = not (atEnd buf) && p (currentChar buf)

notFollowedBy char _ _ _ (AI _ _ buf) 
  = nextCharIs buf (/=char)
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notFollowedBySymbol _ _ _ (AI _ _ buf)
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  = nextCharIs buf (`notElem` "!#$%&*+./<=>?@\\^|-~")
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-- We must reject doc comments as being ordinary comments everywhere.
-- In some cases the doc comment will be selected as the lexeme due to
-- maximal munch, but not always, because the nested comment rule is
-- valid in all states, but the doc-comment rules are only valid in
-- the non-layout states.
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isNormalComment bits _ _ (AI _ _ buf)
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  | haddockEnabled bits = notFollowedByDocOrPragma
  | otherwise           = nextCharIs buf (/='#')
  where
    notFollowedByDocOrPragma
       = not $ spaceAndP buf (`nextCharIs` (`elem` "|^*$#"))

spaceAndP buf p = p buf || nextCharIs buf (==' ') && p (snd (nextChar buf))
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haddockDisabledAnd p bits _ _ (AI _ _ buf)
  = if haddockEnabled bits then False else (p buf)

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atEOL _ _ _ (AI _ _ buf) = atEnd buf || currentChar buf == '\n'
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ifExtension pred bits _ _ _ = pred bits

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multiline_doc_comment :: Action
multiline_doc_comment span buf _len = withLexedDocType (worker "")
  where
    worker commentAcc input docType oneLine = case alexGetChar input of
      Just ('\n', input') 
        | oneLine -> docCommentEnd input commentAcc docType buf span
        | otherwise -> case checkIfCommentLine input' of
          Just input -> worker ('\n':commentAcc) input docType False
          Nothing -> docCommentEnd input commentAcc docType buf span
      Just (c, input) -> worker (c:commentAcc) input docType oneLine
      Nothing -> docCommentEnd input commentAcc docType buf span
      
    checkIfCommentLine input = check (dropNonNewlineSpace input)
      where
        check input = case alexGetChar input of
          Just ('-', input) -> case alexGetChar input of
            Just ('-', input) -> case alexGetChar input of
              Just (c, _) | c /= '-' -> Just input
              _ -> Nothing
            _ -> Nothing
          _ -> Nothing

        dropNonNewlineSpace input = case alexGetChar input of
          Just (c, input') 
            | isSpace c && c /= '\n' -> dropNonNewlineSpace input'
            | otherwise -> input
          Nothing -> input

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{-
  nested comments require traversing by hand, they can't be parsed
  using regular expressions.
-}
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nested_comment :: P (Located Token) -> Action
nested_comment cont span _str _len = do
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  input <- getInput
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  go (1::Int) input
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  where
    go 0 input = do setInput input; cont
    go n input = case alexGetChar input of
      Nothing -> errBrace input span
      Just ('-',input) -> case alexGetChar input of
        Nothing  -> errBrace input span
        Just ('\125',input) -> go (n-1) input
        Just (c,_)          -> go n input
      Just ('\123',input) -> case alexGetChar input of
        Nothing  -> errBrace input span
        Just ('-',input) -> go (n+1) input
        Just (c,_)       -> go n input
      Just (c,input) -> go n input

nested_doc_comment :: Action
nested_doc_comment span buf _len = withLexedDocType (go "")
  where
    go commentAcc input docType _ = case alexGetChar input of
      Nothing -> errBrace input span
      Just ('-',input) -> case alexGetChar input of
        Nothing -> errBrace input span
        Just ('\125',input@(AI end _ buf2)) ->
          docCommentEnd input commentAcc docType buf span
        Just (c,_) -> go ('-':commentAcc) input docType False
      Just ('\123', input) -> case alexGetChar input of
        Nothing  -> errBrace input span
        Just ('-',input) -> do
          setInput input
          let cont = do input <- getInput; go commentAcc input docType False
          nested_comment cont span buf _len
        Just (c,_) -> go ('\123':commentAcc) input docType False
      Just (c,input) -> go (c:commentAcc) input docType False

withLexedDocType lexDocComment = do
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  input@(AI _ _ buf) <- getInput
  case prevChar buf ' ' of
    '|' -> lexDocComment input ITdocCommentNext False
    '^' -> lexDocComment input ITdocCommentPrev False
    '$' -> lexDocComment input ITdocCommentNamed False
    '*' -> lexDocSection 1 input 
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 where 
    lexDocSection n input = case alexGetChar input of 
      Just ('*', input) -> lexDocSection (n+1) input
      Just (c, _) -> lexDocComment input (ITdocSection n) True
      Nothing -> do setInput input; lexToken -- eof reached, lex it normally

-- docCommentEnd
-------------------------------------------------------------------------------
-- This function is quite tricky. We can't just return a new token, we also
-- need to update the state of the parser. Why? Because the token is longer
-- than what was lexed by Alex, and the lexToken function doesn't know this, so 
-- it writes the wrong token length to the parser state. This function is
-- called afterwards, so it can just update the state. 

-- This is complicated by the fact that Haddock tokens can span multiple lines, 
-- which is something that the original lexer didn't account for. 
-- I have added last_line_len in the parser state which represents the length 
-- of the part of the token that is on the last line. It is now used for layout 
-- calculation in pushCurrentContext instead of last_len. last_len is, like it 
-- was before, the full length of the token, and it is now only used for error
-- messages. /Waern 

docCommentEnd :: AlexInput -> String -> (String -> Token) -> StringBuffer ->
                 SrcSpan -> P (Located Token) 
docCommentEnd input commentAcc docType buf span = do
  setInput input
  let (AI loc last_offs nextBuf) = input
      comment = reverse commentAcc
      span' = mkSrcSpan (srcSpanStart span) loc
      last_len = byteDiff buf nextBuf
      
      last_line_len = if (last_offs - last_len < 0) 
        then last_offs
        else last_len  
  
  span `seq` setLastToken span' last_len last_line_len
  return (L span' (docType comment))
 
errBrace (AI end _ _) span = failLocMsgP (srcSpanStart span) end "unterminated `{-'"
 
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open_brace, close_brace :: Action
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open_brace span _str _len = do 
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  ctx <- getContext
  setContext (NoLayout:ctx)
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  return (L span ITocurly)
close_brace span _str _len = do 
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  popContext
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  return (L span ITccurly)
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qvarid buf len = ITqvarid $! splitQualName buf len
qconid buf len = ITqconid $! splitQualName buf len

splitQualName :: StringBuffer -> Int -> (FastString,FastString)
-- takes a StringBuffer and a length, and returns the module name
-- and identifier parts of a qualified name.  Splits at the *last* dot,
-- because of hierarchical module names.
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splitQualName orig_buf len = split orig_buf orig_buf
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  where
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    split buf dot_buf
	| orig_buf `byteDiff` buf >= len  = done dot_buf
	| c == '.'                	  = found_dot buf'
	| otherwise               	  = split buf' dot_buf
      where
       (c,buf') = nextChar buf
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    -- careful, we might get names like M....
    -- so, if the character after the dot is not upper-case, this is
    -- the end of the qualifier part.
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    found_dot buf -- buf points after the '.'
	| isUpper c    = split buf' buf
	| otherwise    = done buf
      where
       (c,buf') = nextChar buf

    done dot_buf =
	(lexemeToFastString orig_buf (qual_size - 1),
	 lexemeToFastString dot_buf (len - qual_size))
      where
	qual_size = orig_buf `byteDiff` dot_buf
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varid span buf len = 
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  case lookupUFM reservedWordsFM fs of
	Just (keyword,0)    -> do
		maybe_layout keyword
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		return (L span keyword)
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	Just (keyword,exts) -> do
		b <- extension (\i -> exts .&. i /= 0)
		if b then do maybe_layout keyword
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			     return (L span keyword)
		     else return (L span (ITvarid fs))
	_other -> return (L span (ITvarid fs))
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  where
	fs = lexemeToFastString buf len

conid buf len = ITconid fs
  where fs = lexemeToFastString buf len

qvarsym buf len = ITqvarsym $! splitQualName buf len
qconsym buf len = ITqconsym $! splitQualName buf len

varsym = sym ITvarsym
consym = sym ITconsym

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sym con span buf len = 
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  case lookupUFM reservedSymsFM fs of
	Just (keyword,exts) -> do
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		b <- extension exts
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		if b then return (L span keyword)
		     else return (L span $! con fs)
	_other -> return (L span $! con fs)
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  where
	fs = lexemeToFastString buf len

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-- Variations on the integral numeric literal.
tok_integral :: (Integer -> Token)
     -> (Integer -> Integer)
 --    -> (StringBuffer -> StringBuffer) -> (Int -> Int)
     -> Int -> Int
     -> (Integer, (Char->Int)) -> Action
tok_integral itint transint transbuf translen (radix,char_to_int) span buf len =
  return $ L span $ itint $! transint $ parseUnsignedInteger
     (offsetBytes transbuf buf) (subtract translen len) radix char_to_int

-- some conveniences for use with tok_integral
tok_num = tok_integral ITinteger
tok_primint = tok_integral ITprimint
positive = id
negative = negate
decimal = (10,octDecDigit)
octal = (8,octDecDigit)
hexadecimal = (16,hexDigit)

-- readRational can understand negative rationals, exponents, everything.
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tok_float        str = ITrational   $! readRational str
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tok_primfloat    str = ITprimfloat  $! readRational str
tok_primdouble   str = ITprimdouble $! readRational str
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-- -----------------------------------------------------------------------------
-- Layout processing

-- we're at the first token on a line, insert layout tokens if necessary
do_bol :: Action
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do_bol span _str _len = do
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	pos <- getOffside
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	case pos of
	    LT -> do
                --trace "layout: inserting '}'" $ do
		popContext
		-- do NOT pop the lex state, we might have a ';' to insert
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		return (L span ITvccurly)
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	    EQ -> do
                --trace "layout: inserting ';'" $ do
		popLexState
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		return (L span ITsemi)
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	    GT -> do
		popLexState
		lexToken

-- certain keywords put us in the "layout" state, where we might
-- add an opening curly brace.
maybe_layout ITdo	= pushLexState layout_do
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maybe_layout ITmdo	= pushLexState layout_do
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maybe_layout ITof	= pushLexState layout
maybe_layout ITlet	= pushLexState layout
maybe_layout ITwhere	= pushLexState layout
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maybe_layout ITrec	= pushLexState layout
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maybe_layout _	        = return ()

-- Pushing a new implicit layout context.  If the indentation of the
-- next token is not greater than the previous layout context, then
-- Haskell 98 says that the new layout context should be empty; that is
-- the lexer must generate {}.
--
-- We are slightly more lenient than this: when the new context is started
-- by a 'do', then we allow the new context to be at the same indentation as
-- the previous context.  This is what the 'strict' argument is for.
--
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new_layout_context strict span _buf _len = do
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    popLexState
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    (AI _ offset _) <- getInput
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    ctx <- getContext
    case ctx of
	Layout prev_off : _  | 
	   (strict     && prev_off >= offset  ||
	    not strict && prev_off > offset) -> do
		-- token is indented to the left of the previous context.
		-- we must generate a {} sequence now.
		pushLexState layout_left
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		return (L span ITvocurly)
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	other -> do
		setContext (Layout offset : ctx)
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		return (L span ITvocurly)
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do_layout_left span _buf _len = do
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    popLexState
    pushLexState bol  -- we must be at the start of a line
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    return (L span ITvccurly)
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-- -----------------------------------------------------------------------------
-- LINE pragmas

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setLine :: Int -> Action
setLine code span buf len = do
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  let line = parseUnsignedInteger buf len 10 octDecDigit
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  setSrcLoc (mkSrcLoc (srcSpanFile span) (fromIntegral line - 1) 0)
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	-- subtract one: the line number refers to the *following* line
  popLexState
  pushLexState code
  lexToken

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setFile :: Int -> Action
setFile code span buf len = do
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  let file = lexemeToFastString (stepOn buf) (len-2)
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  setSrcLoc (mkSrcLoc file (srcSpanEndLine span) (srcSpanEndCol span))
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  popLexState
  pushLexState code
  lexToken

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-- -----------------------------------------------------------------------------
-- Options, includes and language pragmas.

lex_string_prag :: (String -> Token) -> Action
lex_string_prag mkTok span buf len
    = do input <- getInput
         start <- getSrcLoc
         tok <- go [] input
         end <- getSrcLoc
         return (L (mkSrcSpan start end) tok)
    where go acc input
              = if isString input "#-}"
                   then do setInput input
                           return (mkTok (reverse acc))
                   else case alexGetChar input of
                          Just (c,i) -> go (c:acc) i
                          Nothing -> err input
          isString i [] = True
          isString i (x:xs)
              = case alexGetChar i of
                  Just (c,i') | c == x    -> isString i' xs
                  _other -> False
          err (AI end _ _) = failLocMsgP (srcSpanStart span) end "unterminated options pragma"


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-- -----------------------------------------------------------------------------
-- Strings & Chars

-- This stuff is horrible.  I hates it.

lex_string_tok :: Action
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lex_string_tok span buf len = do
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  tok <- lex_string ""
  end <- getSrcLoc 
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  return (L (mkSrcSpan (srcSpanStart span) end) tok)
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lex_string :: String -> P Token
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lex_string s = do
  i <- getInput
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  case alexGetChar' i of
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    Nothing -> lit_error

    Just ('"',i)  -> do
	setInput i
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	magicHash <- extension magicHashEnabled
	if magicHash
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	  then do
	    i <- getInput
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	    case alexGetChar' i of
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	      Just ('#',i) -> do
		   setInput i
		   if any (> '\xFF') s
                    then failMsgP "primitive string literal must contain only characters <= \'\\xFF\'"
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                    else let s' = mkZFastString (reverse s) in
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			 return (ITprimstring s')
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			-- mkZFastString is a hack to avoid encoding the
			-- string in UTF-8.  We just want the exact bytes.
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	      _other ->
		return (ITstring (mkFastString (reverse s)))
	  else
		return (ITstring (mkFastString (reverse s)))

    Just ('\\',i)
	| Just ('&',i) <- next -> do 
		setInput i; lex_string s
	| Just (c,i) <- next, is_space c -> do 
		setInput i; lex_stringgap s
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	where next = alexGetChar' i
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    Just (c, i) -> do
	c' <- lex_char c i
	lex_string (c':s)
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lex_stringgap s = do
  c <- getCharOrFail
  case c of
    '\\' -> lex_string s
    c | is_space c -> lex_stringgap s
    _other -> lit_error


lex_char_tok :: Action
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-- Here we are basically parsing character literals, such as 'x' or '\n'
-- but, when Template Haskell is on, we additionally spot
-- 'x and ''T, returning ITvarQuote and ITtyQuote respectively, 
-- but WIHTOUT CONSUMING the x or T part  (the parser does that).
-- So we have to do two characters of lookahead: when we see 'x we need to
-- see if there's a trailing quote
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lex_char_tok span buf len = do	-- We've seen '
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   i1 <- getInput	-- Look ahead to first character
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   let loc = srcSpanStart span
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   case alexGetChar' i1 of
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	Nothing -> lit_error 

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	Just ('\'', i2@(AI end2 _ _)) -> do 	-- We've seen ''
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		  th_exts <- extension thEnabled
		  if th_exts then do
			setInput i2
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			return (L (mkSrcSpan loc end2)  ITtyQuote)
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		   else lit_error

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	Just ('\\', i2@(AI end2 _ _)) -> do 	-- We've seen 'backslash 
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		  setInput i2
		  lit_ch <- lex_escape
		  mc <- getCharOrFail	-- Trailing quote
		  if mc == '\'' then finish_char_tok loc lit_ch
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			        else do setInput i2; lit_error 
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        Just (c, i2@(AI end2 _ _)) 
		| not (isAny c) -> lit_error
		| otherwise ->
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		-- We've seen 'x, where x is a valid character
		--  (i.e. not newline etc) but not a quote or backslash
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	   case alexGetChar' i2 of	-- Look ahead one more character
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		Nothing -> lit_error
		Just ('\'', i3) -> do 	-- We've seen 'x'
			setInput i3 
			finish_char_tok loc c
		_other -> do 		-- We've seen 'x not followed by quote
					-- If TH is on, just parse the quote only
			th_exts <- extension thEnabled	
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			let (AI end _ _) = i1
			if th_exts then return (L (mkSrcSpan loc end) ITvarQuote)
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				   else do setInput i2; lit_error
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finish_char_tok :: SrcLoc -> Char -> P (Located Token)
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finish_char_tok loc ch	-- We've already seen the closing quote
			-- Just need to check for trailing #
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  = do	magicHash <- extension magicHashEnabled
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	i@(AI end _ _) <- getInput
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	if magicHash then do
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		case alexGetChar' i of
1175
			Just ('#',i@(AI end _ _)) -> do
1176
				setInput i
1177
				return (L (mkSrcSpan loc end) (ITprimchar ch))
1178
			_other ->
1179 1180 1181 1182
				return (L (mkSrcSpan loc end) (ITchar ch))
	        else do
		   return (L (mkSrcSpan loc end) (ITchar ch))

1183 1184 1185 1186 1187
lex_char :: Char -> AlexInput -> P Char
lex_char c inp = do
  case c of
      '\\' -> do setInput inp; lex_escape
      c | isAny c -> do setInput inp; return c
1188
      _other -> lit_error
1189

1190 1191 1192
isAny c | c > '\xff' = isPrint c
	| otherwise  = is_any c

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lex_escape :: P Char
lex_escape = do
  c <- getCharOrFail
  case c of
	'a'   -> return '\a'
	'b'   -> return '\b'
	'f'   -> return '\f'
	'n'   -> return '\n'
	'r'   -> return '\r'
	't'   -> return '\t'
	'v'   -> return '\v'
	'\\'  -> return '\\'
	'"'   -> return '\"'
	'\''  -> return '\''
	'^'   -> do c <- getCharOrFail
		    if c >= '@' && c <= '_'
			then return (chr (ord c - ord '@'))
			else lit_error

1212 1213 1214
	'x'   -> readNum is_hexdigit 16 hexDigit
	'o'   -> readNum is_octdigit  8 octDecDigit
	x | is_digit x -> readNum2 is_digit 10 octDecDigit (octDecDigit x)
1215 1216 1217

	c1 ->  do
	   i <- getInput
1218
	   case alexGetChar' i of
1219 1220
	    Nothing -> lit_error
	    Just (c2,i2) -> 
1221 1222
              case alexGetChar' i2 of
		Nothing	-> do setInput i2; lit_error
1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236
		Just (c3,i3) -> 
		   let str = [c1,c2,c3] in
		   case [ (c,rest) | (p,c) <- silly_escape_chars,
			      	     Just rest <- [maybePrefixMatch p str] ] of
			  (escape_char,[]):_ -> do
				setInput i3
				return escape_char
			  (escape_char,_:_):_ -> do
				setInput i2
				return escape_char
			  [] -> lit_error

readNum :: (Char -> Bool) -> Int -> (Char -> Int) -> P Char
readNum is_digit base conv = do
1237
  i <- getInput
1238 1239 1240
  c <- getCharOrFail
  if is_digit c 
	then readNum2 is_digit base conv (conv c)
1241
	else do setInput i; lit_error
1242 1243 1244 1245 1246

readNum2 is_digit base conv i = do
  input <- getInput
  read i input
  where read i input = do
1247
	  case alexGetChar' input of
1248 1249 1250 1251
	    Just (c,input') | is_digit c -> do
		read (i*base + conv c) input'
	    _other -> do
		if i >= 0 && i <= 0x10FFFF
1252
		   then do setInput input; return (chr i)
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		   else lit_error

silly_escape_chars = [
	("NUL", '\NUL'),
	("SOH", '\SOH'),
	("STX", '\STX'),
	("ETX", '\ETX'),
	("EOT", '\EOT'),
	("ENQ", '\ENQ'),
	("ACK", '\ACK'),
	("BEL", '\BEL'),
	("BS", '\BS'),
	("HT", '\HT'),
	("LF", '\LF'),
	("VT", '\VT'),
	("FF", '\FF'),
	("CR", '\CR'),
	("SO", '\SO'),
	("SI", '\SI'),
	("DLE", '\DLE'),
	("DC1", '\DC1'),
	("DC2", '\DC2'),
	("DC3", '\DC3'),
	("DC4", '\DC4'),
	("NAK", '\NAK'),
	("SYN", '\SYN'),
	("ETB", '\ETB'),
	("CAN", '\CAN'),
	("EM", '\EM'),
	("SUB", '\SUB'),
	("ESC", '\ESC'),
	("FS", '\FS'),
	("GS", '\GS'),
	("RS", '\RS'),
	("US", '\US'),
	("SP", '\SP'),
	("DEL", '\DEL')
	]

1292 1293 1294 1295
-- before calling lit_error, ensure that the current input is pointing to
-- the position of the error in the buffer.  This is so that we can report
-- a correct location to the user, but also so we can detect UTF-8 decoding
-- errors if they occur.
1296 1297 1298 1299 1300
lit_error = lexError "lexical error in string/character literal"

getCharOrFail :: P Char
getCharOrFail =  do
  i <- getInput
1301
  case alexGetChar' i of
1302 1303 1304
	Nothing -> lexError "unexpected end-of-file in string/character literal"
	Just (c,i)  -> do setInput i; return c

1305 1306 1307 1308
-- -----------------------------------------------------------------------------
-- Warnings

warn :: DynFlag -> SDoc -> Action
1309 1310
warn option warning srcspan _buf _len = do
    addWarning option srcspan warning
1311 1312
    lexToken

1313 1314 1315 1316 1317 1318
-- -----------------------------------------------------------------------------
-- The Parse Monad

data LayoutContext
  = NoLayout
  | Layout !Int
1319
  deriving Show
1320 1321 1322 1323

data ParseResult a
  = POk PState a
  | PFailed 
1324
	SrcSpan		-- The start and end of the text span related to
1325 1326
			-- the error.  Might be used in environments which can 
			-- show this span, e.g. by highlighting it.
1327 1328 1329 1330
	Message		-- The error message

data PState = PState { 
	buffer	   :: StringBuffer,
1331 1332
    dflags     :: DynFlags,
    messages   :: Messages,
1333
        last_loc   :: SrcSpan,	-- pos of previous token
1334 1335 1336
        last_offs  :: !Int, 	-- offset of the previous token from the
				-- beginning of  the current line.
				-- \t is equal to 8 spaces.
1337
	last_len   :: !Int,	-- len of previous token
1338
  last_line_len :: !Int,
1339 1340 1341 1342 1343
        loc        :: SrcLoc,   -- current loc (end of prev token + 1)
	extsBitmap :: !Int,	-- bitmap that determines permitted extensions
	context	   :: [LayoutContext],
	lex_state  :: [Int]
     }
1344
	-- last_loc and last_len are used when generating error messages,
1345 1346 1347 1348
	-- and in pushCurrentContext only.  Sigh, if only Happy passed the
	-- current token to happyError, we could at least get rid of last_len.
	-- Getting rid of last_loc would require finding another way to 
	-- implement pushCurrentContext (which is only called from one place).
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newtype P a = P { unP :: PState -> ParseResult a }

instance Monad P where
  return = returnP
  (>>=) = thenP
  fail = failP

returnP :: a -> P a
returnP a = P $ \s -> POk s a

thenP :: P a -> (a -> P b) -> P b
(P m) `thenP` k = P $ \ s ->
	case m s of
1363 1364
		POk s1 a         -> (unP (k a)) s1
		PFailed span err -> PFailed span err
1365 1366

failP :: String -> P a