Token.purs

-- | Primitive parsers for an input stream of type
-- | `(`[__List__](https://pursuit.purescript.org/packages/purescript-lists/docs/Data.List.Types#t:List) `a)`
-- | for working with streams of tokens.
-- |
-- | This module is a port of the Haskell
-- | [__Text.Parsec.Token__](https://hackage.haskell.org/package/parsec/docs/Text-Parsec-Token.html)
-- | module.

module Text.Parsing.Parser.Token
  ( token
  , when
  , match
  , eof
  , LanguageDef
  , GenLanguageDef(LanguageDef)
  , unGenLanguageDef
  , TokenParser
  , GenTokenParser
  , makeTokenParser
  , module Text.Parsing.Parser.String.Basic
  ) where

import Prelude hiding (between, when)

import Control.Lazy (fix)
import Control.Monad.State (get, gets, modify_)
import Control.MonadPlus (guard, (<|>))
import Data.Array as Array
import Data.Char (fromCharCode, toCharCode)
import Data.CodePoint.Unicode (hexDigitToInt, isAlpha, isSpace)
import Data.Either (Either(..))
import Data.Foldable (foldl, foldr)
import Data.Identity (Identity)
import Data.Int (toNumber)
import Data.List (List(..))
import Data.List as List
import Data.List.NonEmpty (NonEmptyList)
import Data.Maybe (Maybe(..), maybe)
import Data.String (null, toLower)
import Data.String.CodePoints (codePointFromChar)
import Data.String.CodeUnits (singleton, toChar) as CodeUnits
import Data.String.CodeUnits as SCU
import Data.String.Unicode as Unicode
import Data.Tuple (Tuple(..))
import Math (pow)
import Text.Parsing.Parser (ParseState(..), ParserT, consume, fail)
import Text.Parsing.Parser.Combinators (between, choice, notFollowedBy, option, sepBy, sepBy1, skipMany, skipMany1, try, tryRethrow, (<?>), (<??>))
import Text.Parsing.Parser.Pos (Position)
import Text.Parsing.Parser.String (char, noneOf, oneOf, satisfy, satisfyCodePoint, string)
import Text.Parsing.Parser.String.Basic as Basic
import Text.Parsing.Parser.String.Basic (digit, hexDigit, octDigit, upper, space, letter, alphaNum)

-- | A parser which returns the first token in the stream.
token :: forall m a. Monad m => (a -> Position) -> ParserT (List a) m a
token tokpos = do
  input <- gets \(ParseState input _ _) -> input
  case List.uncons input of
    Nothing -> fail "Unexpected EOF"
    Just { head, tail } -> do
      modify_ \(ParseState _ _ _) ->
        ParseState tail (tokpos head) true
      pure head

-- | A parser which matches any token satisfying the predicate.
when :: forall m a. Monad m => (a -> Position) -> (a -> Boolean) -> ParserT (List a) m a
when tokpos f = tryRethrow do
  a <- token tokpos
  guard $ f a
  pure a

-- | Match the specified token at the head of the stream.
match :: forall a m. Monad m => Eq a => (a -> Position) -> a -> ParserT (List a) m a
match tokpos tok = when tokpos (_ == tok)

-- | Match the “end-of-file,” the end of the input stream.
eof :: forall a m. Monad m => ParserT (List a) m Unit
eof = do
  ParseState input _ _ <- get
  if (List.null input)
  -- We must consume so this combines correctly with notFollowedBy
  then consume
  else (fail "Expected EOF")

type LanguageDef = GenLanguageDef String Identity

-- | The `GenLanguageDef` type is a record that contains all parameterizable
-- | features of the "Text.Parsec.Token" module. The module `Text.Parsec.Language`
-- | contains some default definitions.
newtype GenLanguageDef s m = LanguageDef
  {
    -- | Describes the start of a block comment. Use the empty string if the
    -- | language doesn't support block comments. For example `/*`.
    commentStart :: String

  -- | Describes the end of a block comment. Use the empty string if the
  -- | language doesn't support block comments. For example `*/`.
  , commentEnd :: String

  -- | Describes the start of a line comment. Use the empty string if the
  -- | language doesn't support line comments. For example `//`.
  , commentLine :: String

  -- | Set to `true` if the language supports nested block comments.
  , nestedComments :: Boolean

  -- | This parser should accept any start characters of identifiers. For
  -- | example `letter <|> char '_'`.
  , identStart :: ParserT s m Char

  -- | This parser should accept any legal tail characters of identifiers.
  -- | For example `alphaNum <|> char '_'`.
  , identLetter :: ParserT s m Char

  -- | This parser should accept any start characters of operators. For
  -- | example `oneOf [':', '+', '=']`.
  , opStart :: ParserT s m Char

  -- | This parser should accept any legal tail characters of operators.
  -- | Note that this parser should even be defined if the language doesn't
  -- | support user-defined operators, or otherwise the `reservedOp`
  -- | parser won't work correctly.
  , opLetter :: ParserT s m Char

  -- | The list of reserved identifiers.
  , reservedNames :: Array String

  -- | The list of reserved operators.
  , reservedOpNames :: Array String

  -- | Set to `true` if the language is case sensitive.
  , caseSensitive :: Boolean
  }

unGenLanguageDef
  :: forall s m
   . GenLanguageDef s m
  -> { caseSensitive :: Boolean
     , reservedOpNames :: Array String
     , reservedNames :: Array String
     , opLetter :: ParserT s m Char
     , opStart :: ParserT s m Char
     , identLetter :: ParserT s m Char
     , identStart :: ParserT s m Char
     , nestedComments :: Boolean
     , commentLine :: String
     , commentEnd :: String
     , commentStart :: String
     }
unGenLanguageDef (LanguageDef langDef) = langDef

-----------------------------------------------------------
-- A first class module: TokenParser
-----------------------------------------------------------

type TokenParser = GenTokenParser String Identity

-- | The type of the record that holds lexical parsers that work on
-- | `s` streams over a monad `m`.
type GenTokenParser s m =
  {
    -- | This lexeme parser parses a legal identifier. Returns the identifier
    -- | string. This parser will fail on identifiers that are reserved
    -- | words. Legal identifier (start) characters and reserved words are
    -- | defined in the `LanguageDef` that is passed to
    -- | `makeTokenParser`. An `identifier` is treated as
    -- | a single token using `try`.
    identifier :: ParserT s m String

  -- | The lexeme parser `reserved name` parses `symbol
  -- | name`, but it also checks that the `name` is not a prefix of a
  -- | valid identifier. A `reserved` word is treated as a single token
  -- | using `try`.
  , reserved :: String -> ParserT s m Unit

  -- | This lexeme parser parses a legal operator. Returns the name of the
  -- | operator. This parser will fail on any operators that are reserved
  -- | operators. Legal operator (start) characters and reserved operators
  -- | are defined in the `LanguageDef` that is passed to
  -- | `makeTokenParser`. An `operator` is treated as a
  -- | single token using `try`.
  , operator :: ParserT s m String

  -- |The lexeme parser `reservedOp name` parses `symbol
  -- | name`, but it also checks that the `name` is not a prefix of a
  -- | valid operator. A `reservedOp` is treated as a single token using
  -- | `try`.
  , reservedOp :: String -> ParserT s m Unit

  -- | This lexeme parser parses a single literal character. Returns the
  -- | literal character value. This parsers deals correctly with escape
  -- | sequences. The literal character is parsed according to the grammar
  -- | rules defined in the Haskell report (which matches most programming
  -- | languages quite closely).
  , charLiteral :: ParserT s m Char

  -- | This lexeme parser parses a literal string. Returns the literal
  -- | string value. This parsers deals correctly with escape sequences and
  -- | gaps. The literal string is parsed according to the grammar rules
  -- | defined in the Haskell report (which matches most programming
  -- | languages quite closely).
  , stringLiteral :: ParserT s m String

  -- | This lexeme parser parses a natural number (a positive whole
  -- | number). Returns the value of the number. The number can be
  -- | specified in `decimal`, `hexadecimal` or
  -- | `octal`. The number is parsed according to the grammar
  -- | rules in the Haskell report.
  , natural :: ParserT s m Int

  -- | This lexeme parser parses an integer (a whole number). This parser
  -- | is like `natural` except that it can be prefixed with
  -- | sign (i.e. `-` or `+`). Returns the value of the number. The
  -- | number can be specified in `decimal`, `hexadecimal`
  -- | or `octal`. The number is parsed according
  -- | to the grammar rules in the Haskell report.
  , integer :: ParserT s m Int

  -- | This lexeme parser parses a floating point value. Returns the value
  -- | of the number. The number is parsed according to the grammar rules
  -- | defined in the Haskell report.
  , float :: ParserT s m Number

  -- | This lexeme parser parses either `natural` or a `float`.
  -- | Returns the value of the number. This parsers deals with
  -- | any overlap in the grammar rules for naturals and floats. The number
  -- | is parsed according to the grammar rules defined in the Haskell report.
  , naturalOrFloat :: ParserT s m (Either Int Number)

  -- | Parses a positive whole number in the decimal system. Returns the
  -- | value of the number.
  , decimal :: ParserT s m Int

  -- | Parses a positive whole number in the hexadecimal system. The number
  -- | should be prefixed with `0x` or `0X`. Returns the value of the
  -- | number.
  , hexadecimal :: ParserT s m Int

  -- | Parses a positive whole number in the octal system. The number
  -- | should be prefixed with `0o` or `0O`. Returns the value of the
  -- | number.
  , octal ::
      ParserT s m Int

  -- | Lexeme parser `symbol s` parses `string` `s` and skips
  -- | trailing white space.
  , symbol :: String -> ParserT s m String

  -- | `lexeme p` first applies parser `p` and than the `whiteSpace`
  -- | parser, returning the value of `p`. Every lexical
  -- | token (lexeme) is defined using `lexeme`, this way every parse
  -- | starts at a point without white space. Parsers that use `lexeme` are
  -- | called *lexeme* parsers in this document.
  -- |
  -- | The only point where the `whiteSpace` parser should be
  -- | called explicitly is the start of the main parser in order to skip
  -- | any leading white space.
  -- |
  -- | ```purescript
  -- | mainParser = do
  -- |   whiteSpace
  -- |   ds <- many (lexeme digit)
  -- |   eof
  -- |   pure (sum ds)
  -- | ```
  , lexeme :: forall a. ParserT s m a -> ParserT s m a

  -- | Parses any white space. White space consists of *zero* or more
  -- | occurrences of a `space`, a line comment or a block (multi
  -- | line) comment. Block comments may be nested. How comments are
  -- | started and ended is defined in the `LanguageDef`
  -- | that is passed to `makeTokenParser`.
  , whiteSpace :: ParserT s m Unit

  -- | Lexeme parser `parens p` parses `p` enclosed in parenthesis,
  -- | returning the value of `p`.
  , parens :: forall a. ParserT s m a -> ParserT s m a

  -- | Lexeme parser `braces p` parses `p` enclosed in braces (`{` and
  -- | `}`), returning the value of `p`.
  , braces :: forall a. ParserT s m a -> ParserT s m a

  -- | Lexeme parser `angles p` parses `p` enclosed in angle brackets (`<`
  -- | and `>`), returning the value of `p`.
  , angles :: forall a. ParserT s m a -> ParserT s m a

  -- | Lexeme parser `brackets p` parses `p` enclosed in brackets (`[`
  -- | and `]`), returning the value of `p`.
  , brackets :: forall a. ParserT s m a -> ParserT s m a

  -- | Lexeme parser `semi` parses the character `;` and skips any
  -- | trailing white space. Returns the string `;`.
  , semi :: ParserT s m String

  -- | Lexeme parser `comma` parses the character `,` and skips any
  -- | trailing white space. Returns the string `,`.
  , comma :: ParserT s m String

  -- | Lexeme parser `colon` parses the character `:` and skips any
  -- | trailing white space. Returns the string `:`.
  , colon :: ParserT s m String

  -- | Lexeme parser `dot` parses the character `.` and skips any
  -- | trailing white space. Returns the string `.`.
  , dot :: ParserT s m String

  -- | Lexeme parser `semiSep p` parses *zero* or more occurrences of `p`
  -- | separated by `semi`. Returns a list of values pureed by
  -- | `p`.
  , semiSep :: forall a. ParserT s m a -> ParserT s m (List a)

  -- | Lexeme parser `semiSep1 p` parses *one* or more occurrences of `p`
  -- | separated by `semi`. Returns a list of values pureed by `p`.
  , semiSep1 :: forall a. ParserT s m a -> ParserT s m (NonEmptyList a)

  -- | Lexeme parser `commaSep p` parses *zero* or more occurrences of
  -- | `p` separated by `comma`. Returns a list of values pureed
  -- | by `p`.
  , commaSep :: forall a. ParserT s m a -> ParserT s m (List a)

  -- | Lexeme parser `commaSep1 p` parses *one* or more occurrences of
  -- | `p` separated by `comma`. Returns a list of values pureed
  -- | by `p`.
  , commaSep1 :: forall a. ParserT s m a -> ParserT s m (NonEmptyList a)
  }

-----------------------------------------------------------
-- Given a LanguageDef, create a token parser.
-----------------------------------------------------------

-- | The expression `makeTokenParser language` creates a `GenTokenParser`
-- | record that contains lexical parsers that are
-- | defined using the definitions in the `language` record.
-- |
-- | The use of this function is quite stylized - one imports the
-- | appropiate language definition and selects the lexical parsers that
-- | are needed from the resulting `GenTokenParser`.
-- |
-- | ```purescript
-- | module Main where
-- |
-- | import Text.Parsing.Parser.Language (haskellDef)
-- | import Text.Parsing.Parser.Token (makeTokenParser)
-- |
-- | -- The parser
-- | expr = parens expr
-- |    <|> identifier
-- |    <|> ...
-- |
-- |
-- | -- The lexer
-- | tokenParser = makeTokenParser haskellDef
-- | parens      = tokenParser.parens
-- | braces      = tokenParser.braces
-- | identifier  = tokenParser.identifier
-- | reserved    = tokenParser.reserved
-- | ...
-- | ```
makeTokenParser :: forall m. Monad m => GenLanguageDef String m -> GenTokenParser String m
makeTokenParser (LanguageDef languageDef) =
  { identifier: identifier
  , reserved: reserved
  , operator: operator
  , reservedOp: reservedOp

  , charLiteral: charLiteral
  , stringLiteral: stringLiteral
  , natural: natural
  , integer: integer
  , float: float
  , naturalOrFloat: naturalOrFloat
  , decimal: decimal
  , hexadecimal: hexadecimal
  , octal: octal

  , symbol: symbol
  , lexeme: lexeme
  , whiteSpace: whiteSpace' (LanguageDef languageDef)

  , parens: parens
  , braces: braces
  , angles: angles
  , brackets: brackets
  , semi: semi
  , comma: comma
  , colon: colon
  , dot: dot
  , semiSep: semiSep
  , semiSep1: semiSep1
  , commaSep: commaSep
  , commaSep1: commaSep1
  }
  where
  -----------------------------------------------------------
  -- Bracketing
  -----------------------------------------------------------
  parens :: forall a. ParserT String m a -> ParserT String m a
  parens p = between (symbol "(") (symbol ")") p

  braces :: forall a. ParserT String m a -> ParserT String m a
  braces p = between (symbol "{") (symbol "}") p

  angles :: forall a. ParserT String m a -> ParserT String m a
  angles p = between (symbol "<") (symbol ">") p

  brackets :: forall a. ParserT String m a -> ParserT String m a
  brackets p = between (symbol "[") (symbol "]") p

  semi :: ParserT String m String
  semi = symbol ";"

  comma :: ParserT String m String
  comma = symbol ","

  dot :: ParserT String m String
  dot = symbol "."

  colon :: ParserT String m String
  colon = symbol ":"

  commaSep :: forall a. ParserT String m a -> ParserT String m (List a)
  commaSep p = sepBy p comma

  semiSep :: forall a. ParserT String m a -> ParserT String m (List a)
  semiSep p = sepBy p semi

  commaSep1 :: forall a. ParserT String m a -> ParserT String m (NonEmptyList a)
  commaSep1 p = sepBy1 p comma

  semiSep1 :: forall a. ParserT String m a -> ParserT String m (NonEmptyList a)
  semiSep1 p = sepBy1 p semi

  -----------------------------------------------------------
  -- Chars & Strings
  -----------------------------------------------------------
  charLiteral :: ParserT String m Char
  charLiteral = lexeme go <?> "character"
    where
    go :: ParserT String m Char
    go = between (char '\'') (char '\'' <?> "end of character") characterChar

  characterChar :: ParserT String m Char
  characterChar = charLetter <|> charEscape <?> "literal character"

  charEscape :: ParserT String m Char
  charEscape = char '\\' *> escapeCode

  charLetter :: ParserT String m Char
  charLetter = satisfy \c -> (c /= '\'') && (c /= '\\') && (c > '\x1A')

  stringLiteral :: ParserT String m String
  stringLiteral = lexeme (go <?> "literal string")
    where
    go :: ParserT String m String
    go = do
      maybeChars <- between (char '"') (char '"' <?> "end of string") (List.many stringChar)
      pure $ SCU.fromCharArray $ List.toUnfoldable $ foldr folder Nil maybeChars

    folder :: Maybe Char -> List Char -> List Char
    folder Nothing chars = chars
    folder (Just c) chars = Cons c chars

  stringChar :: ParserT String m (Maybe Char)
  stringChar = (Just <$> stringLetter)
    <|> stringEscape
    <?> "string character"

  stringLetter :: ParserT String m Char
  stringLetter = satisfy (\c -> (c /= '"') && (c /= '\\') && (c > '\x1A'))

  stringEscape :: ParserT String m (Maybe Char)
  stringEscape = do
    _ <- char '\\'
    (escapeGap $> Nothing) <|> (escapeEmpty $> Nothing) <|> (Just <$> escapeCode)

  escapeEmpty :: ParserT String m Char
  escapeEmpty = char '&'

  escapeGap :: ParserT String m Char
  escapeGap = Array.some Basic.space *> char '\\' <?> "end of string gap"

  -- -- escape codes
  escapeCode :: ParserT String m Char
  escapeCode = charEsc <|> charNum <|> charAscii <|> charControl
    <?> "escape code"

  charControl :: ParserT String m Char
  charControl = do
    _ <- char '^'
    code <- Basic.upper
    case fromCharCode (toCharCode code - toCharCode 'A' + 1) of
      Just c -> pure c
      Nothing -> fail "invalid character code (should not happen)"

  charNum :: ParserT String m Char
  charNum = do
    code <- decimal
      <|> (char 'o' *> number 8 Basic.octDigit)
      <|> (char 'x' *> number 16 Basic.hexDigit)
    if code > 0x10FFFF then fail "invalid escape sequence"
    else case fromCharCode code of
      Just c -> pure c
      Nothing -> fail "invalid character code (should not happen)"

  charEsc :: ParserT String m Char
  charEsc = choice (map parseEsc escMap)
    where
    parseEsc :: Tuple Char Char -> ParserT String m Char
    parseEsc (Tuple c code) = char c $> code

  charAscii :: ParserT String m Char
  charAscii = choice (map parseAscii asciiMap)
    where
    parseAscii :: Tuple String Char -> ParserT String m Char
    parseAscii (Tuple asc code) = try $ string asc $> code

  -- escape code tables
  escMap :: Array (Tuple Char Char)
  escMap =
    Array.zip
      [ 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', '\"', '\'' ]
      [ '\x7', '\x8', '\xC', '\n', '\r', '\t', '\xB', '\\', '\"', '\'' ]

  asciiMap :: Array (Tuple String Char)
  asciiMap = Array.zip (ascii3codes <> ascii2codes) (ascii3 <> ascii2)

  ascii2codes :: Array String
  ascii2codes = [ "BS", "HT", "LF", "VT", "FF", "CR", "SO", "SI", "EM", "FS", "GS", "RS", "US", "SP" ]

  ascii3codes :: Array String
  ascii3codes =
    [ "NUL"
    , "SOH"
    , "STX"
    , "ETX"
    , "EOT"
    , "ENQ"
    , "ACK"
    , "BEL"
    , "DLE"
    , "DC1"
    , "DC2"
    , "DC3"
    , "DC4"
    , "NAK"
    , "SYN"
    , "ETB"
    , "CAN"
    , "SUB"
    , "ESC"
    , "DEL"
    ]

  ascii2 :: Array Char
  ascii2 =
    [ '\x8'
    , '\x9'
    , '\xA'
    , '\xB'
    , '\xC'
    , '\xD'
    , '\xE'
    , '\xF'
    , '\x19'
    , '\x1C'
    , '\x1D'
    , '\x1E'
    , '\x1F'
    , '\x20'
    ]

  ascii3 :: Array Char
  ascii3 =
    [ '\x0'
    , '\x1'
    , '\x2'
    , '\x3'
    , '\x4'
    , '\x5'
    , '\x6'
    , '\x7'
    , '\x10'
    , '\x11'
    , '\x12'
    , '\x13'
    , '\x14'
    , '\x15'
    , '\x16'
    , '\x17'
    , '\x18'
    , '\x1A'
    , '\x1B'
    , '\x7F'
    ]

  -----------------------------------------------------------
  -- Numbers
  -----------------------------------------------------------

  naturalOrFloat :: ParserT String m (Either Int Number)
  naturalOrFloat = lexeme (natFloat) <?> "number"

  float :: ParserT String m Number
  float = lexeme floating <?> "float"

  integer :: ParserT String m Int
  integer = lexeme int <?> "integer"

  natural :: ParserT String m Int
  natural = lexeme nat <?> "natural"

  -- floats
  floating :: ParserT String m Number
  floating = decimal >>= fractExponent

  natFloat :: ParserT String m (Either Int Number)
  natFloat = char '0' *> zeroNumFloat
    <|> decimalFloat

  zeroNumFloat :: ParserT String m (Either Int Number)
  zeroNumFloat = Left <$> (hexadecimal <|> octal)
    <|> decimalFloat
    <|> fractFloat 0
    <|> pure (Left 0)

  decimalFloat :: ParserT String m (Either Int Number)
  decimalFloat = do
    n <- decimal
    option (Left n) (fractFloat n)

  fractFloat :: forall a. Int -> ParserT String m (Either a Number)
  fractFloat n = Right <$> fractExponent n

  fractExponent :: Int -> ParserT String m Number
  fractExponent n = fractExponent' <|> justExponent
    where
    fractExponent' :: ParserT String m Number
    fractExponent' = do
      fract <- fraction
      expo <- option 1.0 exponent'
      pure $ (toNumber n + fract) * expo

    justExponent :: ParserT String m Number
    justExponent = do
      expo <- exponent'
      pure $ (toNumber n * expo)

  fraction :: ParserT String m Number
  fraction = "fraction" <??> do
    _ <- char '.'
    digits <- Array.some Basic.digit <?> "fraction"
    maybe (fail "not digit") pure $ foldr op (Just 0.0) digits
    where
    op :: Char -> Maybe Number -> Maybe Number
    op _ Nothing = Nothing
    op d (Just f) = do
      int' <- hexDigitToInt $ codePointFromChar d
      pure $ (f + toNumber int') / 10.0

  exponent' :: ParserT String m Number
  exponent' = "exponent" <??> do
    _ <- oneOf [ 'e', 'E' ]
    f <- sign
    e <- decimal <?> "exponent"
    pure $ power (f e)
    where
    power :: Int -> Number
    power e
      | e < 0 = 1.0 / power (-e)
      | otherwise = 10.0 `pow` toNumber e

  -- integers and naturals
  int :: ParserT String m Int
  int = do
    f <- lexeme sign
    n <- nat
    pure $ f n

  sign :: forall a. (Ring a) => ParserT String m (a -> a)
  sign = (char '-' $> negate)
    <|> (char '+' $> identity)
    <|> pure identity

  nat :: ParserT String m Int
  nat = zeroNumber <|> decimal

  zeroNumber :: ParserT String m Int
  zeroNumber =
    char '0' *>
      (hexadecimal <|> octal <|> decimal <|> pure 0) <?> ""

  decimal :: ParserT String m Int
  decimal = number 10 Basic.digit

  hexadecimal :: ParserT String m Int
  hexadecimal = oneOf [ 'x', 'X' ] *> number 16 Basic.hexDigit

  octal :: ParserT String m Int
  octal = oneOf [ 'o', 'O' ] *> number 8 Basic.octDigit

  number :: Int -> ParserT String m Char -> ParserT String m Int
  number base baseDigit = do
    digits <- Array.some baseDigit
    maybe (fail "not digits") pure $ foldl folder (Just 0) digits
    where
    folder :: Maybe Int -> Char -> Maybe Int
    folder Nothing _ = Nothing
    folder (Just x) d = ((base * x) + _) <$> hexDigitToInt (codePointFromChar d)

  -----------------------------------------------------------
  -- Operators & reserved ops
  -----------------------------------------------------------

  reservedOp :: String -> ParserT String m Unit
  reservedOp name = lexeme $ try go
    where
    go :: ParserT String m Unit
    go = do
      _ <- string name
      notFollowedBy languageDef.opLetter <?> "end of " <> name

  operator :: ParserT String m String
  operator = lexeme $ try go
    where
    go :: ParserT String m String
    go = do
      name <- oper
      if (isReservedOp name) then fail ("reserved operator " <> name)
      else pure name

  oper :: ParserT String m String
  oper = go <?> "operator"
    where
    go :: ParserT String m String
    go = do
      c <- languageDef.opStart
      cs <- Array.many languageDef.opLetter
      pure $ SCU.singleton c <> SCU.fromCharArray cs

  isReservedOp :: String -> Boolean
  isReservedOp name = isReserved (Array.sort languageDef.reservedOpNames) name

  -----------------------------------------------------------
  -- Identifiers & Reserved words
  -----------------------------------------------------------

  reserved :: String -> ParserT String m Unit
  reserved name = lexeme $ try go
    where
    go :: ParserT String m Unit
    go = caseString name *> (notFollowedBy languageDef.identLetter <?> "end of " <> name)

  caseString :: String -> ParserT String m String
  caseString name
    | languageDef.caseSensitive = string name $> name
    | otherwise = walk name $> name
        where
        walk :: String -> ParserT String m Unit
        walk name' = case SCU.uncons name' of
          Nothing -> pure unit
          Just { head: c, tail: cs } -> (caseChar c <?> msg) *> walk cs

        caseChar :: Char -> ParserT String m Char
        caseChar c
          | isAlpha (codePointFromChar c)
          , Just c1 <- CodeUnits.toChar (Unicode.toLowerSimple $ CodeUnits.singleton c)
          , Just c2 <- CodeUnits.toChar (Unicode.toUpperSimple $ CodeUnits.singleton c) =
              char c1 <|> char c2
          | otherwise = char c

        msg :: String
        msg = show name

  identifier :: ParserT String m String
  identifier = lexeme $ try go
    where
    go :: ParserT String m String
    go = do
      name <- ident
      if (isReservedName (LanguageDef languageDef) name) then fail ("reserved word " <> show name)
      else pure name

  ident :: ParserT String m String
  ident = go <?> "identifier"
    where
    go :: ParserT String m String
    go = do
      c <- languageDef.identStart
      cs <- Array.many languageDef.identLetter
      pure $ SCU.singleton c <> SCU.fromCharArray cs

  -----------------------------------------------------------
  -- White space & symbols
  -----------------------------------------------------------
  symbol :: String -> ParserT String m String
  symbol name = lexeme (string name) $> name

  lexeme :: forall a. ParserT String m a -> ParserT String m a
  lexeme p = p <* whiteSpace' (LanguageDef languageDef)

-- ================================================================================ --
-- The following functions should really be in the where-clause of makeTokenParser, --
-- but they can't go there because they are mutually recursive.                     --
-- ================================================================================ --

-----------------------------------------------------------
-- Identifiers & Reserved words
-----------------------------------------------------------

isReservedName :: forall m. Monad m => GenLanguageDef String m -> String -> Boolean
isReservedName langDef@(LanguageDef languageDef) name =
  isReserved (theReservedNames langDef) caseName
  where
  caseName
    | languageDef.caseSensitive = name
    | otherwise = toLower name

isReserved :: Array String -> String -> Boolean
isReserved names name =
  case Array.uncons names of
    Nothing -> false
    Just { head: r, tail: rs } -> case (compare r name) of
      LT -> isReserved rs name
      EQ -> true
      GT -> false

theReservedNames :: forall m. Monad m => GenLanguageDef String m -> Array String
theReservedNames (LanguageDef languageDef)
  | languageDef.caseSensitive = Array.sort languageDef.reservedNames
  | otherwise = Array.sort $ map toLower languageDef.reservedNames

-----------------------------------------------------------
-- White space & symbols
-----------------------------------------------------------

whiteSpace' :: forall m. Monad m => GenLanguageDef String m -> ParserT String m Unit
whiteSpace' langDef@(LanguageDef languageDef)
  | null languageDef.commentLine && null languageDef.commentStart =
      skipMany (simpleSpace <?> "")
  | null languageDef.commentLine =
      skipMany (simpleSpace <|> multiLineComment langDef <?> "")
  | null languageDef.commentStart =
      skipMany (simpleSpace <|> oneLineComment langDef <?> "")
  | otherwise =
      skipMany (simpleSpace <|> oneLineComment langDef <|> multiLineComment langDef <?> "")

simpleSpace :: forall m. Monad m => ParserT String m Unit
simpleSpace = skipMany1 (satisfyCodePoint isSpace)

oneLineComment :: forall m. Monad m => GenLanguageDef String m -> ParserT String m Unit
oneLineComment (LanguageDef languageDef) =
  try (string languageDef.commentLine) *> skipMany (satisfy (_ /= '\n'))

multiLineComment :: forall m. Monad m => GenLanguageDef String m -> ParserT String m Unit
multiLineComment langDef@(LanguageDef languageDef) =
  try (string languageDef.commentStart) *> inComment langDef

inComment :: forall m. Monad m => GenLanguageDef String m -> ParserT String m Unit
inComment langDef@(LanguageDef languageDef) =
  if languageDef.nestedComments then inCommentMulti langDef else inCommentSingle langDef

inCommentMulti :: forall m. Monad m => GenLanguageDef String m -> ParserT String m Unit
inCommentMulti langDef@(LanguageDef languageDef) =
  fix \p -> (void $ try (string languageDef.commentEnd))
    <|> (multiLineComment langDef *> p)
    <|> (skipMany1 (noneOf startEnd) *> p)
    <|> (oneOf startEnd *> p)
    <?> "end of comment"
  where
  startEnd :: Array Char
  startEnd = SCU.toCharArray languageDef.commentEnd <> SCU.toCharArray languageDef.commentStart

inCommentSingle :: forall m. Monad m => GenLanguageDef String m -> ParserT String m Unit
inCommentSingle (LanguageDef languageDef) =
  fix \p -> (void $ try (string languageDef.commentEnd))
    <|> (skipMany1 (noneOf startEnd) *> p)
    <|> (oneOf startEnd *> p)
    <?> "end of comment"
  where
  startEnd :: Array Char
  startEnd = SCU.toCharArray languageDef.commentEnd <> SCU.toCharArray languageDef.commentStart