2b3c97e1af
- Don't immediately throw custom parse errors into 'ParsecT'; rather, just construct and return them - This anticipates the re-implementation of an 'ExceptT' layer of the parser, which should be able throw custom parse errors
246 lines
8.5 KiB
Haskell
246 lines
8.5 KiB
Haskell
{-# LANGUAGE BangPatterns #-}
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{-# LANGUAGE FlexibleContexts #-}
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{-# LANGUAGE LambdaCase #-}
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{-# LANGUAGE PackageImports #-}
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{-# LANGUAGE ScopedTypeVariables #-}
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{-# LANGUAGE StandaloneDeriving #-}
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module Text.Megaparsec.Custom (
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-- * Custom parse error type
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CustomErr,
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-- * Constructing custom parse errors
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parseErrorAt,
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parseErrorAtRegion,
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withSource,
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-- * Pretty-printing custom parse errors
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customParseErrorPretty
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)
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where
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import Prelude ()
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import "base-compat-batteries" Prelude.Compat hiding (readFile)
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import Data.Foldable (asum, toList)
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import qualified Data.List.NonEmpty as NE
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import Data.Proxy (Proxy (Proxy))
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import qualified Data.Set as S
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import Data.Text (Text)
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import Data.Void (Void)
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import Text.Megaparsec
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--- * Custom parse error type
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-- | A custom error type for the parser. The type is specialized to
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-- parsers of 'Text' streams.
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data CustomErr
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-- | Fail with a message at a specific source position interval. The
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-- interval must be contained within a single line.
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= ErrorFailAt SourcePos -- Starting position
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Pos -- Ending position (column; same line as start)
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String -- Error message
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-- | Attach a source file to a parse error (for error reporting from
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-- include files, e.g. with the 'region' parser combinator)
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| ErrorWithSource Text -- Source file contents
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(ParseError Char CustomErr) -- The original
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deriving (Show, Eq, Ord)
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-- We require an 'Ord' instance for 'CustomError' so that they may be
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-- stored in a 'Set'. The actual instance is inconsequential, so we just
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-- derive it, but this requires an (orphan) instance for 'ParseError'.
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-- Hopefully this does not cause any trouble.
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deriving instance (Ord c, Ord e) => Ord (ParseError c e)
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instance ShowErrorComponent CustomErr where
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showErrorComponent (ErrorFailAt _ _ errMsg) = errMsg
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showErrorComponent (ErrorWithSource _ e) = parseErrorTextPretty e
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--- * Constructing custom parse errors
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-- | Fail at a specific source position.
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parseErrorAt :: SourcePos -> String -> CustomErr
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parseErrorAt pos msg = ErrorFailAt pos (sourceColumn pos) msg
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-- | Fail at a specific source interval (within a single line). The
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-- interval is inclusive on the left and exclusive on the right; that is,
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-- it spans from the start position to just before (and not including) the
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-- end position.
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parseErrorAtRegion
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:: SourcePos -- ^ Start position
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-> SourcePos -- ^ End position
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-> String -- ^ Error message
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-> CustomErr
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parseErrorAtRegion startPos endPos msg =
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let startCol = sourceColumn startPos
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endCol' = mkPos $ subtract 1 $ unPos $ sourceColumn endPos
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endCol = if startCol <= endCol'
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&& sourceLine startPos == sourceLine endPos
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then endCol' else startCol
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in ErrorFailAt startPos endCol msg
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-- | Attach a source file to a parse error. Intended for use with the
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-- 'region' parser combinator.
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withSource :: Text -> ParseError Char CustomErr -> ParseError Char CustomErr
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withSource s e =
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FancyError (errorPos e) $ S.singleton $ ErrorCustom $ ErrorWithSource s e
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--- * Pretty-printing custom parse errors
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-- | Pretty-print our custom parse errors and display the line on which
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-- the parse error occured. Use this instead of 'parseErrorPretty'.
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--
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-- If any custom errors are present, arbitrarily take the first one (since
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-- only one custom error should be used at a time).
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customParseErrorPretty :: Text -> ParseError Char CustomErr -> String
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customParseErrorPretty source err = case findCustomError err of
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Nothing -> customParseErrorPretty' source err pos1
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Just (ErrorWithSource customSource customErr) ->
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customParseErrorPretty customSource customErr
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Just (ErrorFailAt sourcePos col errMsg) ->
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let newPositionStack = sourcePos NE.:| NE.tail (errorPos err)
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errorIntervalLength = mkPos $ max 1 $
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unPos col - unPos (sourceColumn sourcePos) + 1
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newErr :: ParseError Char Void
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newErr = FancyError newPositionStack (S.singleton (ErrorFail errMsg))
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in customParseErrorPretty' source newErr errorIntervalLength
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where
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findCustomError :: ParseError Char CustomErr -> Maybe CustomErr
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findCustomError err = case err of
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FancyError _ errSet ->
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finds (\case {ErrorCustom e -> Just e; _ -> Nothing}) errSet
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_ -> Nothing
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finds :: (Foldable t) => (a -> Maybe b) -> t a -> Maybe b
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finds f = asum . map f . toList
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--- * Modified Megaparsec source
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-- The below code has been copied from Megaparsec (v.6.4.1,
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-- Text.Megaparsec.Error) and modified to suit our needs. These changes are
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-- indicated by square brackets. The following copyright notice, conditions,
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-- and disclaimer apply to all code below this point.
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--
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-- Copyright © 2015–2018 Megaparsec contributors<br>
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-- Copyright © 2007 Paolo Martini<br>
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-- Copyright © 1999–2000 Daan Leijen
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--
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-- All rights reserved.
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--
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-- Redistribution and use in source and binary forms, with or without
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-- modification, are permitted provided that the following conditions are met:
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--
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-- * Redistributions of source code must retain the above copyright notice,
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-- this list of conditions and the following disclaimer.
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--
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-- * Redistributions in binary form must reproduce the above copyright notice,
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-- this list of conditions and the following disclaimer in the documentation
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-- and/or other materials provided with the distribution.
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--
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-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS “AS IS” AND ANY EXPRESS
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-- OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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-- OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN
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-- NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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-- INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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-- LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
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-- OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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-- LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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-- NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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-- EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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-- | Pretty-print a 'ParseError Char CustomErr' and display the line on
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-- which the parse error occurred. The rendered 'String' always ends with
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-- a newline.
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customParseErrorPretty'
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:: ( ShowToken (Token s)
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, LineToken (Token s)
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, ShowErrorComponent e
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, Stream s )
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=> s -- ^ Original input stream
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-> ParseError (Token s) e -- ^ Parse error to render
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-> Pos -- ^ Length of error interval [added]
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-> String -- ^ Result of rendering
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customParseErrorPretty' = customParseErrorPretty_ defaultTabWidth
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customParseErrorPretty_
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:: forall s e.
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( ShowToken (Token s)
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, LineToken (Token s)
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, ShowErrorComponent e
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, Stream s )
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=> Pos -- ^ Tab width
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-> s -- ^ Original input stream
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-> ParseError (Token s) e -- ^ Parse error to render
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-> Pos -- ^ Length of error interval [added]
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-> String -- ^ Result of rendering
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customParseErrorPretty_ w s e l =
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sourcePosStackPretty (errorPos e) <> ":\n" <>
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padding <> "|\n" <>
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lineNumber <> " | " <> rline <> "\n" <>
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padding <> "| " <> rpadding <> highlight <> "\n" <> -- [added `highlight`]
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parseErrorTextPretty e
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where
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epos = NE.head (errorPos e) -- [changed from NE.last to NE.head]
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lineNumber = (show . unPos . sourceLine) epos
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padding = replicate (length lineNumber + 1) ' '
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rpadding = replicate (unPos (sourceColumn epos) - 1) ' '
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highlight = replicate (unPos l) '^' -- [added]
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rline =
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case rline' of
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[] -> "<empty line>"
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xs -> expandTab w xs
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rline' = fmap tokenAsChar . chunkToTokens (Proxy :: Proxy s) $
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selectLine (sourceLine epos) s
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-- | Select a line from input stream given its number.
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selectLine
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:: forall s. (LineToken (Token s), Stream s)
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=> Pos -- ^ Number of line to select
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-> s -- ^ Input stream
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-> Tokens s -- ^ Selected line
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selectLine l = go pos1
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where
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go !n !s =
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if n == l
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then fst (takeWhile_ notNewline s)
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else go (n <> pos1) (stripNewline $ snd (takeWhile_ notNewline s))
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notNewline = not . tokenIsNewline
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stripNewline s =
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case take1_ s of
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Nothing -> s
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Just (_, s') -> s'
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-- | Replace tab characters with given number of spaces.
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expandTab
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:: Pos
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-> String
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-> String
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expandTab w' = go 0
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where
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go 0 [] = []
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go 0 ('\t':xs) = go w xs
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go 0 (x:xs) = x : go 0 xs
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go !n xs = ' ' : go (n - 1) xs
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w = unPos w'
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