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- # lexer.coffee

- ¶

  The CoffeeScript Lexer. Uses a series of token-matching regexes to attempt matches against the beginning of the source code. When a match is found, a token is produced, we consume the match, and start again. Tokens are in the form:

      [tag, value, locationData]

  where locationData is {first_line, first_column, last_line, last_column}, which is a format that can be fed directly into Jison. These are read by jison in the `parser.lexer` function defined in coffee-script.coffee.

      {Rewriter, INVERSES} = require './rewriter'

- ¶

  Import the helpers we need.

      {count, starts, compact, repeat, invertLiterate,
      locationDataToString,  throwSyntaxError} = require './helpers'

- ¶

  ## The Lexer Class

- ¶
- ¶

  The Lexer class reads a stream of CoffeeScript and divvies it up into tagged tokens. Some potential ambiguity in the grammar has been avoided by pushing some extra smarts into the Lexer.

      exports.Lexer = class Lexer

- ¶

  tokenize is the Lexer’s main method. Scan by attempting to match tokens one at a time, using a regular expression anchored at the start of the remaining code, or a custom recursive token-matching method (for interpolations). When the next token has been recorded, we move forward within the code past the token, and begin again.

  Each tokenizing method is responsible for returning the number of characters it has consumed.

  Before returning the token stream, run it through the Rewriter.

        tokenize: (code, opts = {}) ->
          @literate   = opts.literate  # Are we lexing literate CoffeeScript?
          @indent     = 0              # The current indentation level.
          @baseIndent = 0              # The overall minimum indentation level
          @indebt     = 0              # The over-indentation at the current level.
          @outdebt    = 0              # The under-outdentation at the current level.
          @indents    = []             # The stack of all current indentation levels.
          @ends       = []             # The stack for pairing up tokens.
          @tokens     = []             # Stream of parsed tokens in the form `['TYPE', value, location data]`.
          @seenFor    = no             # Used to recognize FORIN, FOROF and FORFROM tokens.
          @seenImport = no             # Used to recognize IMPORT FROM? AS? tokens.
          @seenExport = no             # Used to recognize EXPORT FROM? AS? tokens.
          @importSpecifierList = no    # Used to identify when in an IMPORT {...} FROM? ...
          @exportSpecifierList = no    # Used to identify when in an EXPORT {...} FROM? ...

          @chunkLine =
            opts.line or 0             # The start line for the current @chunk.
          @chunkColumn =
            opts.column or 0           # The start column of the current @chunk.
          code = @clean code           # The stripped, cleaned original source code.

- ¶

  At every position, run through this list of attempted matches, short-circuiting if any of them succeed. Their order determines precedence: `@literalToken` is the fallback catch-all.

          i = 0
          while @chunk = code[i..]
            consumed = \
                 @identifierToken() or
                 @commentToken()    or
                 @whitespaceToken() or
                 @lineToken()       or
                 @stringToken()     or
                 @numberToken()     or
                 @regexToken()      or
                 @jsToken()         or
                 @literalToken()

- ¶

  Update position

            [@chunkLine, @chunkColumn] = @getLineAndColumnFromChunk consumed

            i += consumed

            return {@tokens, index: i} if opts.untilBalanced and @ends.length is 0

          @closeIndentation()
          @error "missing #{end.tag}", end.origin[2] if end = @ends.pop()
          return @tokens if opts.rewrite is off
          (new Rewriter).rewrite @tokens

- ¶

  Preprocess the code to remove leading and trailing whitespace, carriage returns, etc. If we’re lexing literate CoffeeScript, strip external Markdown by removing all lines that aren’t indented by at least four spaces or a tab.

        clean: (code) ->
          code = code.slice(1) if code.charCodeAt(0) is BOM
          code = code.replace(/\r/g, '').replace TRAILING_SPACES, ''
          if WHITESPACE.test code
            code = "\n#{code}"
            @chunkLine--
          code = invertLiterate code if @literate
          code

- ¶

  ## Tokenizers

- ¶
- ¶

  Matches identifying literals: variables, keywords, method names, etc. Check to ensure that JavaScript reserved words aren’t being used as identifiers. Because CoffeeScript reserves a handful of keywords that are allowed in JavaScript, we’re careful not to tag them as keywords when referenced as property names here, so you can still do `jQuery.is()` even though `is` means `===` otherwise.

        identifierToken: ->
          return 0 unless match = IDENTIFIER.exec @chunk
          [input, id, colon] = match

- ¶

  Preserve length of id for location data

          idLength = id.length
          poppedToken = undefined

          if id is 'own' and @tag() is 'FOR'
            @token 'OWN', id
            return id.length
          if id is 'from' and @tag() is 'YIELD'
            @token 'FROM', id
            return id.length
          if id is 'as' and @seenImport
            if @value() is '*'
              @tokens[@tokens.length - 1][0] = 'IMPORT_ALL'
            else if @value() in COFFEE_KEYWORDS
              @tokens[@tokens.length - 1][0] = 'IDENTIFIER'
            if @tag() in ['DEFAULT', 'IMPORT_ALL', 'IDENTIFIER']
              @token 'AS', id
              return id.length
          if id is 'as' and @seenExport and @tag() in ['IDENTIFIER', 'DEFAULT']
            @token 'AS', id
            return id.length
          if id is 'default' and @seenExport and @tag() in ['EXPORT', 'AS']
            @token 'DEFAULT', id
            return id.length

          [..., prev] = @tokens

          tag =
            if colon or prev? and
               (prev[0] in ['.', '?.', '::', '?::'] or
               not prev.spaced and prev[0] is '@')
              'PROPERTY'
            else
              'IDENTIFIER'

          if tag is 'IDENTIFIER' and (id in JS_KEYWORDS or id in COFFEE_KEYWORDS) and
             not (@exportSpecifierList and id in COFFEE_KEYWORDS)
            tag = id.toUpperCase()
            if tag is 'WHEN' and @tag() in LINE_BREAK
              tag = 'LEADING_WHEN'
            else if tag is 'FOR'
              @seenFor = yes
            else if tag is 'UNLESS'
              tag = 'IF'
            else if tag is 'IMPORT'
              @seenImport = yes
            else if tag is 'EXPORT'
              @seenExport = yes
            else if tag in UNARY
              tag = 'UNARY'
            else if tag in RELATION
              if tag isnt 'INSTANCEOF' and @seenFor
                tag = 'FOR' + tag
                @seenFor = no
              else
                tag = 'RELATION'
                if @value() is '!'
                  poppedToken = @tokens.pop()
                  id = '!' + id
          else if tag is 'IDENTIFIER' and @seenFor and id is 'from' and
             isForFrom(prev)
            tag = 'FORFROM'
            @seenFor = no

          if tag is 'IDENTIFIER' and id in RESERVED
            @error "reserved word '#{id}'", length: id.length

          unless tag is 'PROPERTY'
            if id in COFFEE_ALIASES
              alias = id
              id = COFFEE_ALIAS_MAP[id]
            tag = switch id
              when '!'                 then 'UNARY'
              when '==', '!='          then 'COMPARE'
              when 'true', 'false'     then 'BOOL'
              when 'break', 'continue', \
                   'debugger'          then 'STATEMENT'
              when '&&', '||'          then id
              else  tag

          tagToken = @token tag, id, 0, idLength
          tagToken.origin = [tag, alias, tagToken[2]] if alias
          if poppedToken
            [tagToken[2].first_line, tagToken[2].first_column] =
              [poppedToken[2].first_line, poppedToken[2].first_column]
          if colon
            colonOffset = input.lastIndexOf ':'
            @token ':', ':', colonOffset, colon.length

          input.length

- ¶

  Matches numbers, including decimals, hex, and exponential notation. Be careful not to interfere with ranges-in-progress.

        numberToken: ->
          return 0 unless match = NUMBER.exec @chunk

          number = match[0]
          lexedLength = number.length

          switch
            when /^0[BOX]/.test number
              @error "radix prefix in '#{number}' must be lowercase", offset: 1
            when /^(?!0x).*E/.test number
              @error "exponential notation in '#{number}' must be indicated with a lowercase 'e'",
                offset: number.indexOf('E')
            when /^0\d*[89]/.test number
              @error "decimal literal '#{number}' must not be prefixed with '0'", length: lexedLength
            when /^0\d+/.test number
              @error "octal literal '#{number}' must be prefixed with '0o'", length: lexedLength

          base = switch number.charAt 1
            when 'b' then 2
            when 'o' then 8
            when 'x' then 16
            else null
          numberValue = if base? then parseInt(number[2..], base) else parseFloat(number)
          if number.charAt(1) in ['b', 'o']
            number = "0x#{numberValue.toString 16}"

          tag = if numberValue is Infinity then 'INFINITY' else 'NUMBER'
          @token tag, number, 0, lexedLength
          lexedLength

- ¶

  Matches strings, including multi-line strings, as well as heredocs, with or without interpolation.

        stringToken: ->
          [quote] = STRING_START.exec(@chunk) || []
          return 0 unless quote

- ¶

  If the preceding token is `from` and this is an import or export statement, properly tag the `from`.

          if @tokens.length and @value() is 'from' and (@seenImport or @seenExport)
            @tokens[@tokens.length - 1][0] = 'FROM'

          regex = switch quote
            when "'"   then STRING_SINGLE
            when '"'   then STRING_DOUBLE
            when "'''" then HEREDOC_SINGLE
            when '"""' then HEREDOC_DOUBLE
          heredoc = quote.length is 3

          {tokens, index: end} = @matchWithInterpolations regex, quote
          $ = tokens.length - 1

          delimiter = quote.charAt(0)
          if heredoc

- ¶

  Find the smallest indentation. It will be removed from all lines later.

            indent = null
            doc = (token[1] for token, i in tokens when token[0] is 'NEOSTRING').join '#{}'
            while match = HEREDOC_INDENT.exec doc
              attempt = match[1]
              indent = attempt if indent is null or 0 < attempt.length < indent.length
            indentRegex = /// \n#{indent} ///g if indent
            @mergeInterpolationTokens tokens, {delimiter}, (value, i) =>
              value = @formatString value, delimiter: quote
              value = value.replace indentRegex, '\n' if indentRegex
              value = value.replace LEADING_BLANK_LINE,  '' if i is 0
              value = value.replace TRAILING_BLANK_LINE, '' if i is $
              value
          else
            @mergeInterpolationTokens tokens, {delimiter}, (value, i) =>
              value = @formatString value, delimiter: quote
              value = value.replace SIMPLE_STRING_OMIT, (match, offset) ->
                if (i is 0 and offset is 0) or
                   (i is $ and offset + match.length is value.length)
                  ''
                else
                  ' '
              value

          end

- ¶

  Matches and consumes comments.

        commentToken: ->
          return 0 unless match = @chunk.match COMMENT
          [comment, here] = match
          if here
            if match = HERECOMMENT_ILLEGAL.exec comment
              @error "block comments cannot contain #{match[0]}",
                offset: match.index, length: match[0].length
            if here.indexOf('\n') >= 0
              here = here.replace /// \n #{repeat ' ', @indent} ///g, '\n'
            @token 'HERECOMMENT', here, 0, comment.length
          comment.length

- ¶

  Matches JavaScript interpolated directly into the source via backticks.

        jsToken: ->
          return 0 unless @chunk.charAt(0) is '`' and
            (match = HERE_JSTOKEN.exec(@chunk) or JSTOKEN.exec(@chunk))

- ¶

  Convert escaped backticks to backticks, and escaped backslashes just before escaped backticks to backslashes

          script = match[1].replace /\\+(`|$)/g, (string) ->

- ¶

  `string` is always a value like ‘`‘, ‘\`‘, ‘\\`‘, etc. By reducing it to its latter half, we turn ‘`‘ to ‘`', '\\\`‘ to ‘`‘, etc.

            string[-Math.ceil(string.length / 2)..]
          @token 'JS', script, 0, match[0].length
          match[0].length

- ¶

  Matches regular expression literals, as well as multiline extended ones. Lexing regular expressions is difficult to distinguish from division, so we borrow some basic heuristics from JavaScript and Ruby.

        regexToken: ->
          switch
            when match = REGEX_ILLEGAL.exec @chunk
              @error "regular expressions cannot begin with #{match[2]}",
                offset: match.index + match[1].length
            when match = @matchWithInterpolations HEREGEX, '///'
              {tokens, index} = match
            when match = REGEX.exec @chunk
              [regex, body, closed] = match
              @validateEscapes body, isRegex: yes, offsetInChunk: 1
              body = @formatRegex body, delimiter: '/'
              index = regex.length
              [..., prev] = @tokens
              if prev
                if prev.spaced and prev[0] in CALLABLE
                  return 0 if not closed or POSSIBLY_DIVISION.test regex
                else if prev[0] in NOT_REGEX
                  return 0
              @error 'missing / (unclosed regex)' unless closed
            else
              return 0

          [flags] = REGEX_FLAGS.exec @chunk[index..]
          end = index + flags.length
          origin = @makeToken 'REGEX', null, 0, end
          switch
            when not VALID_FLAGS.test flags
              @error "invalid regular expression flags #{flags}", offset: index, length: flags.length
            when regex or tokens.length is 1
              body ?= @formatHeregex tokens[0][1]
              @token 'REGEX', "#{@makeDelimitedLiteral body, delimiter: '/'}#{flags}", 0, end, origin
            else
              @token 'REGEX_START', '(', 0, 0, origin
              @token 'IDENTIFIER', 'RegExp', 0, 0
              @token 'CALL_START', '(', 0, 0
              @mergeInterpolationTokens tokens, {delimiter: '"', double: yes}, @formatHeregex
              if flags
                @token ',', ',', index - 1, 0
                @token 'STRING', '"' + flags + '"', index - 1, flags.length
              @token ')', ')', end - 1, 0
              @token 'REGEX_END', ')', end - 1, 0

          end

- ¶

  Matches newlines, indents, and outdents, and determines which is which. If we can detect that the current line is continued onto the next line, then the newline is suppressed:

      elements
        .each( ... )
        .map( ... )

  Keeps track of the level of indentation, because a single outdent token can close multiple indents, so we need to know how far in we happen to be.

        lineToken: ->
          return 0 unless match = MULTI_DENT.exec @chunk
          indent = match[0]

          @seenFor = no
          @seenImport = no unless @importSpecifierList
          @seenExport = no unless @exportSpecifierList

          size = indent.length - 1 - indent.lastIndexOf '\n'
          noNewlines = @unfinished()

          if size - @indebt is @indent
            if noNewlines then @suppressNewlines() else @newlineToken 0
            return indent.length

          if size > @indent
            if noNewlines
              @indebt = size - @indent
              @suppressNewlines()
              return indent.length
            unless @tokens.length
              @baseIndent = @indent = size
              return indent.length
            diff = size - @indent + @outdebt
            @token 'INDENT', diff, indent.length - size, size
            @indents.push diff
            @ends.push {tag: 'OUTDENT'}
            @outdebt = @indebt = 0
            @indent = size
          else if size < @baseIndent
            @error 'missing indentation', offset: indent.length
          else
            @indebt = 0
            @outdentToken @indent - size, noNewlines, indent.length
          indent.length

- ¶

  Record an outdent token or multiple tokens, if we happen to be moving back inwards past several recorded indents. Sets new @indent value.

        outdentToken: (moveOut, noNewlines, outdentLength) ->
          decreasedIndent = @indent - moveOut
          while moveOut > 0
            lastIndent = @indents[@indents.length - 1]
            if not lastIndent
              moveOut = 0
            else if lastIndent is @outdebt
              moveOut -= @outdebt
              @outdebt = 0
            else if lastIndent < @outdebt
              @outdebt -= lastIndent
              moveOut  -= lastIndent
            else
              dent = @indents.pop() + @outdebt
              if outdentLength and @chunk[outdentLength] in INDENTABLE_CLOSERS
                decreasedIndent -= dent - moveOut
                moveOut = dent
              @outdebt = 0

- ¶

  pair might call outdentToken, so preserve decreasedIndent

              @pair 'OUTDENT'
              @token 'OUTDENT', moveOut, 0, outdentLength
              moveOut -= dent
          @outdebt -= moveOut if dent
          @tokens.pop() while @value() is ';'

          @token 'TERMINATOR', '\n', outdentLength, 0 unless @tag() is 'TERMINATOR' or noNewlines
          @indent = decreasedIndent
          this

- ¶

  Matches and consumes non-meaningful whitespace. Tag the previous token as being “spaced”, because there are some cases where it makes a difference.

        whitespaceToken: ->
          return 0 unless (match = WHITESPACE.exec @chunk) or
                          (nline = @chunk.charAt(0) is '\n')
          [..., prev] = @tokens
          prev[if match then 'spaced' else 'newLine'] = true if prev
          if match then match[0].length else 0

- ¶

  Generate a newline token. Consecutive newlines get merged together.

        newlineToken: (offset) ->
          @tokens.pop() while @value() is ';'
          @token 'TERMINATOR', '\n', offset, 0 unless @tag() is 'TERMINATOR'
          this

- ¶

  Use a `\` at a line-ending to suppress the newline. The slash is removed here once its job is done.

        suppressNewlines: ->
          @tokens.pop() if @value() is '\\'
          this

- ¶

  We treat all other single characters as a token. E.g.: `( ) , . !` Multi-character operators are also literal tokens, so that Jison can assign the proper order of operations. There are some symbols that we tag specially here. `;` and newlines are both treated as a `TERMINATOR`, we distinguish parentheses that indicate a method call from regular parentheses, and so on.

        literalToken: ->
          if match = OPERATOR.exec @chunk
            [value] = match
            @tagParameters() if CODE.test value
          else
            value = @chunk.charAt 0
          tag  = value
          [..., prev] = @tokens

          if prev and value in ['=', COMPOUND_ASSIGN...]
            skipToken = false
            if value is '=' and prev[1] in ['||', '&&'] and not prev.spaced
              prev[0] = 'COMPOUND_ASSIGN'
              prev[1] += '='
              prev = @tokens[@tokens.length - 2]
              skipToken = true
            if prev and prev[0] isnt 'PROPERTY'
              origin = prev.origin ? prev
              message = isUnassignable prev[1], origin[1]
              @error message, origin[2] if message
            return value.length if skipToken

          if value is '{' and @seenImport
            @importSpecifierList = yes
          else if @importSpecifierList and value is '}'
            @importSpecifierList = no
          else if value is '{' and prev?[0] is 'EXPORT'
            @exportSpecifierList = yes
          else if @exportSpecifierList and value is '}'
            @exportSpecifierList = no

          if value is ';'
            @seenFor = @seenImport = @seenExport = no
            tag = 'TERMINATOR'
          else if value is '*' and prev[0] is 'EXPORT'
            tag = 'EXPORT_ALL'
          else if value in MATH            then tag = 'MATH'
          else if value in COMPARE         then tag = 'COMPARE'
          else if value in COMPOUND_ASSIGN then tag = 'COMPOUND_ASSIGN'
          else if value in UNARY           then tag = 'UNARY'
          else if value in UNARY_MATH      then tag = 'UNARY_MATH'
          else if value in SHIFT           then tag = 'SHIFT'
          else if value is '?' and prev?.spaced then tag = 'BIN?'
          else if prev and not prev.spaced
            if value is '(' and prev[0] in CALLABLE
              prev[0] = 'FUNC_EXIST' if prev[0] is '?'
              tag = 'CALL_START'
            else if value is '[' and prev[0] in INDEXABLE
              tag = 'INDEX_START'
              switch prev[0]
                when '?'  then prev[0] = 'INDEX_SOAK'
          token = @makeToken tag, value
          switch value
            when '(', '{', '[' then @ends.push {tag: INVERSES[value], origin: token}
            when ')', '}', ']' then @pair value
          @tokens.push token
          value.length

- ¶

  ## Token Manipulators

- ¶
- ¶

  A source of ambiguity in our grammar used to be parameter lists in function definitions versus argument lists in function calls. Walk backwards, tagging parameters specially in order to make things easier for the parser.

        tagParameters: ->
          return this if @tag() isnt ')'
          stack = []
          {tokens} = this
          i = tokens.length
          tokens[--i][0] = 'PARAM_END'
          while tok = tokens[--i]
            switch tok[0]
              when ')'
                stack.push tok
              when '(', 'CALL_START'
                if stack.length then stack.pop()
                else if tok[0] is '('
                  tok[0] = 'PARAM_START'
                  return this
                else return this
          this

- ¶

  Close up all remaining open blocks at the end of the file.

        closeIndentation: ->
          @outdentToken @indent

- ¶

  Match the contents of a delimited token and expand variables and expressions inside it using Ruby-like notation for substitution of arbitrary expressions.

      "Hello #{name.capitalize()}."

  If it encounters an interpolation, this method will recursively create a new Lexer and tokenize until the `{` of `#{` is balanced with a `}`.

  - `regex` matches the contents of a token (but not `delimiter`, and not `#{` if interpolations are desired).
  - `delimiter` is the delimiter of the token. Examples are `'`, `"`, `'''`, `"""` and `///`.

  This method allows us to have strings within interpolations within strings, ad infinitum.

        matchWithInterpolations: (regex, delimiter) ->
          tokens = []
          offsetInChunk = delimiter.length
          return null unless @chunk[...offsetInChunk] is delimiter
          str = @chunk[offsetInChunk..]
          loop
            [strPart] = regex.exec str

            @validateEscapes strPart, {isRegex: delimiter.charAt(0) is '/', offsetInChunk}

- ¶

  Push a fake ‘NEOSTRING’ token, which will get turned into a real string later.

            tokens.push @makeToken 'NEOSTRING', strPart, offsetInChunk

            str = str[strPart.length..]
            offsetInChunk += strPart.length

            break unless str[...2] is '#{'

- ¶

  The `1`s are to remove the `#` in `#{`.

            [line, column] = @getLineAndColumnFromChunk offsetInChunk + 1
            {tokens: nested, index} =
              new Lexer().tokenize str[1..], line: line, column: column, untilBalanced: on

- ¶

  Skip the trailing `}`.

            index += 1

- ¶

  Turn the leading and trailing `{` and `}` into parentheses. Unnecessary parentheses will be removed later.

            [open, ..., close] = nested
            open[0]  = open[1]  = '('
            close[0] = close[1] = ')'
            close.origin = ['', 'end of interpolation', close[2]]

- ¶

  Remove leading ‘TERMINATOR’ (if any).

            nested.splice 1, 1 if nested[1]?[0] is 'TERMINATOR'

- ¶

  Push a fake ‘TOKENS’ token, which will get turned into real tokens later.

            tokens.push ['TOKENS', nested]

            str = str[index..]
            offsetInChunk += index

          unless str[...delimiter.length] is delimiter
            @error "missing #{delimiter}", length: delimiter.length

          [firstToken, ..., lastToken] = tokens
          firstToken[2].first_column -= delimiter.length
          if lastToken[1].substr(-1) is '\n'
            lastToken[2].last_line += 1
            lastToken[2].last_column = delimiter.length - 1
          else
            lastToken[2].last_column += delimiter.length
          lastToken[2].last_column -= 1 if lastToken[1].length is 0

          {tokens, index: offsetInChunk + delimiter.length}

- ¶

  Merge the array `tokens` of the fake token types ‘TOKENS’ and ‘NEOSTRING’ (as returned by `matchWithInterpolations`) into the token stream. The value of ‘NEOSTRING’s are converted using `fn` and turned into strings using `options` first.

        mergeInterpolationTokens: (tokens, options, fn) ->
          if tokens.length > 1
            lparen = @token 'STRING_START', '(', 0, 0

          firstIndex = @tokens.length
          for token, i in tokens
            [tag, value] = token
            switch tag
              when 'TOKENS'

- ¶

  Optimize out empty interpolations (an empty pair of parentheses).

                continue if value.length is 2

- ¶

  Push all the tokens in the fake ‘TOKENS’ token. These already have sane location data.

                locationToken = value[0]
                tokensToPush = value
              when 'NEOSTRING'

- ¶

  Convert ‘NEOSTRING’ into ‘STRING’.

                converted = fn.call this, token[1], i

- ¶

  Optimize out empty strings. We ensure that the tokens stream always starts with a string token, though, to make sure that the result really is a string.

                if converted.length is 0
                  if i is 0
                    firstEmptyStringIndex = @tokens.length
                  else
                    continue

- ¶

  However, there is one case where we can optimize away a starting empty string.

                if i is 2 and firstEmptyStringIndex?
                  @tokens.splice firstEmptyStringIndex, 2 # Remove empty string and the plus.
                token[0] = 'STRING'
                token[1] = @makeDelimitedLiteral converted, options
                locationToken = token
                tokensToPush = [token]
            if @tokens.length > firstIndex

- ¶

  Create a 0-length “+” token.

              plusToken = @token '+', '+'
              plusToken[2] =
                first_line:   locationToken[2].first_line
                first_column: locationToken[2].first_column
                last_line:    locationToken[2].first_line
                last_column:  locationToken[2].first_column
            @tokens.push tokensToPush...

          if lparen
            [..., lastToken] = tokens
            lparen.origin = ['STRING', null,
              first_line:   lparen[2].first_line
              first_column: lparen[2].first_column
              last_line:    lastToken[2].last_line
              last_column:  lastToken[2].last_column
            ]
            rparen = @token 'STRING_END', ')'
            rparen[2] =
              first_line:   lastToken[2].last_line
              first_column: lastToken[2].last_column
              last_line:    lastToken[2].last_line
              last_column:  lastToken[2].last_column

- ¶

  Pairs up a closing token, ensuring that all listed pairs of tokens are correctly balanced throughout the course of the token stream.

        pair: (tag) ->
          [..., prev] = @ends
          unless tag is wanted = prev?.tag
            @error "unmatched #{tag}" unless 'OUTDENT' is wanted

- ¶

  Auto-close INDENT to support syntax like this:

      el.click((event) ->
        el.hide())

            [..., lastIndent] = @indents
            @outdentToken lastIndent, true
            return @pair tag
          @ends.pop()

- ¶

  ## Helpers

- ¶
- ¶

  Returns the line and column number from an offset into the current chunk.

  `offset` is a number of characters into @chunk.

        getLineAndColumnFromChunk: (offset) ->
          if offset is 0
            return [@chunkLine, @chunkColumn]

          if offset >= @chunk.length
            string = @chunk
          else
            string = @chunk[..offset-1]

          lineCount = count string, '\n'

          column = @chunkColumn
          if lineCount > 0
            [..., lastLine] = string.split '\n'
            column = lastLine.length
          else
            column += string.length

          [@chunkLine + lineCount, column]

- ¶

  Same as “token”, exception this just returns the token without adding it to the results.

        makeToken: (tag, value, offsetInChunk = 0, length = value.length) ->
          locationData = {}
          [locationData.first_line, locationData.first_column] =
            @getLineAndColumnFromChunk offsetInChunk

- ¶

  Use length - 1 for the final offset - we’re supplying the last_line and the last_column, so if last_column == first_column, then we’re looking at a character of length 1.

          lastCharacter = if length > 0 then (length - 1) else 0
          [locationData.last_line, locationData.last_column] =
            @getLineAndColumnFromChunk offsetInChunk + lastCharacter

          token = [tag, value, locationData]

          token

- ¶

  Add a token to the results. `offset` is the offset into the current @chunk where the token starts. `length` is the length of the token in the @chunk, after the offset. If not specified, the length of `value` will be used.

  Returns the new token.

        token: (tag, value, offsetInChunk, length, origin) ->
          token = @makeToken tag, value, offsetInChunk, length
          token.origin = origin if origin
          @tokens.push token
          token

- ¶

  Peek at the last tag in the token stream.

        tag: ->
          [..., token] = @tokens
          token?[0]

- ¶

  Peek at the last value in the token stream.

        value: ->
          [..., token] = @tokens
          token?[1]

- ¶

  Are we in the midst of an unfinished expression?

        unfinished: ->
          LINE_CONTINUER.test(@chunk) or
          @tag() in UNFINISHED

        formatString: (str, options) ->
          @replaceUnicodeCodePointEscapes str.replace(STRING_OMIT, '$1'), options

        formatHeregex: (str) ->
          @formatRegex str.replace(HEREGEX_OMIT, '$1$2'), delimiter: '///'

        formatRegex: (str, options) ->
          @replaceUnicodeCodePointEscapes str, options

        unicodeCodePointToUnicodeEscapes: (codePoint) ->
          toUnicodeEscape = (val) ->
            str = val.toString 16
            "\\u#{repeat '0', 4 - str.length}#{str}"
          return toUnicodeEscape(codePoint) if codePoint < 0x10000

- ¶

  surrogate pair

          high = Math.floor((codePoint - 0x10000) / 0x400) + 0xD800
          low = (codePoint - 0x10000) % 0x400 + 0xDC00
          "#{toUnicodeEscape(high)}#{toUnicodeEscape(low)}"

- ¶

  Replace \u{…} with \uxxxx[\uxxxx] in strings and regexes

        replaceUnicodeCodePointEscapes: (str, options) ->
          str.replace UNICODE_CODE_POINT_ESCAPE, (match, escapedBackslash, codePointHex, offset) =>
            return escapedBackslash if escapedBackslash

            codePointDecimal = parseInt codePointHex, 16
            if codePointDecimal > 0x10ffff
              @error "unicode code point escapes greater than \\u{10ffff} are not allowed",
                offset: offset + options.delimiter.length
                length: codePointHex.length + 4

            @unicodeCodePointToUnicodeEscapes codePointDecimal

- ¶

  Validates escapes in strings and regexes.

        validateEscapes: (str, options = {}) ->
          invalidEscapeRegex =
            if options.isRegex
              REGEX_INVALID_ESCAPE
            else
              STRING_INVALID_ESCAPE
          match = invalidEscapeRegex.exec str
          return unless match
          [[], before, octal, hex, unicodeCodePoint, unicode] = match
          message =
            if octal
              "octal escape sequences are not allowed"
            else
              "invalid escape sequence"
          invalidEscape = "\\#{octal or hex or unicodeCodePoint or unicode}"
          @error "#{message} #{invalidEscape}",
            offset: (options.offsetInChunk ? 0) + match.index + before.length
            length: invalidEscape.length

- ¶

  Constructs a string or regex by escaping certain characters.

        makeDelimitedLiteral: (body, options = {}) ->
          body = '(?:)' if body is '' and options.delimiter is '/'
          regex = ///
              (\\\\)                               # escaped backslash
            | (\\0(?=[1-7]))                       # nul character mistaken as octal escape
            | \\?(#{options.delimiter})            # (possibly escaped) delimiter
            | \\?(?: (\n)|(\r)|(\u2028)|(\u2029) ) # (possibly escaped) newlines
            | (\\.)                                # other escapes
          ///g
          body = body.replace regex, (match, backslash, nul, delimiter, lf, cr, ls, ps, other) -> switch

- ¶

  Ignore escaped backslashes.

            when backslash then (if options.double then backslash + backslash else backslash)
            when nul       then '\\x00'
            when delimiter then "\\#{delimiter}"
            when lf        then '\\n'
            when cr        then '\\r'
            when ls        then '\\u2028'
            when ps        then '\\u2029'
            when other     then (if options.double then "\\#{other}" else other)
          "#{options.delimiter}#{body}#{options.delimiter}"

- ¶

  Throws an error at either a given offset from the current chunk or at the location of a token (`token[2]`).

        error: (message, options = {}) ->
          location =
            if 'first_line' of options
              options
            else
              [first_line, first_column] = @getLineAndColumnFromChunk options.offset ? 0
              {first_line, first_column, last_column: first_column + (options.length ? 1) - 1}
          throwSyntaxError message, location

- ¶

  ## Helper functions

- ¶

      isUnassignable = (name, displayName = name) -> switch
        when name in [JS_KEYWORDS..., COFFEE_KEYWORDS...]
          "keyword '#{displayName}' can't be assigned"
        when name in STRICT_PROSCRIBED
          "'#{displayName}' can't be assigned"
        when name in RESERVED
          "reserved word '#{displayName}' can't be assigned"
        else
          false

      exports.isUnassignable = isUnassignable

- ¶

  `from` isn’t a CoffeeScript keyword, but it behaves like one in `import` and `export` statements (handled above) and in the declaration line of a `for` loop. Try to detect when `from` is a variable identifier and when it is this “sometimes” keyword.

      isForFrom = (prev) ->
        if prev[0] is 'IDENTIFIER'

- ¶

  `for i from from`, `for from from iterable`

          if prev[1] is 'from'
            prev[1][0] = 'IDENTIFIER'
            yes

- ¶

  `for i from iterable`

          yes

- ¶

  `for from…`

        else if prev[0] is 'FOR'
          no

- ¶

  `for {from}…`, `for [from]…`, `for {a, from}…`, `for {a: from}…`

        else if prev[1] in ['{', '[', ',', ':']
          no
        else
          yes

- ¶

  ## Constants

- ¶
- ¶

  Keywords that CoffeeScript shares in common with JavaScript.

      JS_KEYWORDS = [
        'true', 'false', 'null', 'this'
        'new', 'delete', 'typeof', 'in', 'instanceof'
        'return', 'throw', 'break', 'continue', 'debugger', 'yield'
        'if', 'else', 'switch', 'for', 'while', 'do', 'try', 'catch', 'finally'
        'class', 'extends', 'super'
        'import', 'export', 'default'
      ]

- ¶

  CoffeeScript-only keywords.

      COFFEE_KEYWORDS = [
        'undefined', 'Infinity', 'NaN'
        'then', 'unless', 'until', 'loop', 'of', 'by', 'when'
      ]

      COFFEE_ALIAS_MAP =
        and  : '&&'
        or   : '||'
        is   : '=='
        isnt : '!='
        not  : '!'
        yes  : 'true'
        no   : 'false'
        on   : 'true'
        off  : 'false'

      COFFEE_ALIASES  = (key for key of COFFEE_ALIAS_MAP)
      COFFEE_KEYWORDS = COFFEE_KEYWORDS.concat COFFEE_ALIASES

- ¶

  The list of keywords that are reserved by JavaScript, but not used, or are used by CoffeeScript internally. We throw an error when these are encountered, to avoid having a JavaScript error at runtime.

      RESERVED = [
        'case', 'function', 'var', 'void', 'with', 'const', 'let', 'enum'
        'native', 'implements', 'interface', 'package', 'private'
        'protected', 'public', 'static'
      ]

      STRICT_PROSCRIBED = ['arguments', 'eval']

- ¶

  The superset of both JavaScript keywords and reserved words, none of which may be used as identifiers or properties.

      exports.JS_FORBIDDEN = JS_KEYWORDS.concat(RESERVED).concat(STRICT_PROSCRIBED)

- ¶

  The character code of the nasty Microsoft madness otherwise known as the BOM.

      BOM = 65279

- ¶

  Token matching regexes.

      IDENTIFIER = /// ^
        (?!\d)
        ( (?: (?!\s)[$\w\x7f-\uffff] )+ )
        ( [^\n\S]* : (?!:) )?  # Is this a property name?
      ///

      NUMBER     = ///
        ^ 0b[01]+    |              # binary
        ^ 0o[0-7]+   |              # octal
        ^ 0x[\da-f]+ |              # hex
        ^ \d*\.?\d+ (?:e[+-]?\d+)?  # decimal
      ///i

      OPERATOR   = /// ^ (
        ?: [-=]>             # function
         | [-+*/%<>&|^!?=]=  # compound assign / compare
         | >>>=?             # zero-fill right shift
         | ([-+:])\1         # doubles
         | ([&|<>*/%])\2=?   # logic / shift / power / floor division / modulo
         | \?(\.|::)         # soak access
         | \.{2,3}           # range or splat
      ) ///

      WHITESPACE = /^[^\n\S]+/

      COMMENT    = /^###([^#][\s\S]*?)(?:###[^\n\S]*|###$)|^(?:\s*#(?!##[^#]).*)+/

      CODE       = /^[-=]>/

      MULTI_DENT = /^(?:\n[^\n\S]*)+/

      JSTOKEN      = ///^ `(?!``) ((?: [^`\\] | \\[\s\S]           )*) `   ///
      HERE_JSTOKEN = ///^ ```     ((?: [^`\\] | \\[\s\S] | `(?!``) )*) ``` ///

- ¶

  String-matching-regexes.

      STRING_START   = /^(?:'''|"""|'|")/

      STRING_SINGLE  = /// ^(?: [^\\']  | \\[\s\S]                      )* ///
      STRING_DOUBLE  = /// ^(?: [^\\"#] | \\[\s\S] |           \#(?!\{) )* ///
      HEREDOC_SINGLE = /// ^(?: [^\\']  | \\[\s\S] | '(?!'')            )* ///
      HEREDOC_DOUBLE = /// ^(?: [^\\"#] | \\[\s\S] | "(?!"") | \#(?!\{) )* ///

      STRING_OMIT    = ///
          ((?:\\\\)+)      # consume (and preserve) an even number of backslashes
        | \\[^\S\n]*\n\s*  # remove escaped newlines
      ///g
      SIMPLE_STRING_OMIT = /\s*\n\s*/g
      HEREDOC_INDENT     = /\n+([^\n\S]*)(?=\S)/g

- ¶

  Regex-matching-regexes.

      REGEX = /// ^
        / (?!/) ((
        ?: [^ [ / \n \\ ]  # every other thing
         | \\[^\n]         # anything but newlines escaped
         | \[              # character class
             (?: \\[^\n] | [^ \] \n \\ ] )*
           \]
        )*) (/)?
      ///

      REGEX_FLAGS  = /^\w*/
      VALID_FLAGS  = /^(?!.*(.).*\1)[imguy]*$/

      HEREGEX      = /// ^(?: [^\\/#] | \\[\s\S] | /(?!//) | \#(?!\{) )* ///

      HEREGEX_OMIT = ///
          ((?:\\\\)+)     # consume (and preserve) an even number of backslashes
        | \\(\s)          # preserve escaped whitespace
        | \s+(?:#.*)?     # remove whitespace and comments
      ///g

      REGEX_ILLEGAL = /// ^ ( / | /{3}\s*) (\*) ///

      POSSIBLY_DIVISION   = /// ^ /=?\s ///

- ¶

  Other regexes.

      HERECOMMENT_ILLEGAL = /\*\//

      LINE_CONTINUER      = /// ^ \s* (?: , | \??\.(?![.\d]) | :: ) ///

      STRING_INVALID_ESCAPE = ///
        ( (?:^|[^\\]) (?:\\\\)* )        # make sure the escape isn’t escaped
        \\ (
           ?: (0[0-7]|[1-7])             # octal escape
            | (x(?![\da-fA-F]{2}).{0,2}) # hex escape
            | (u\{(?![\da-fA-F]{1,}\})[^}]*\}?) # unicode code point escape
            | (u(?!\{|[\da-fA-F]{4}).{0,4}) # unicode escape
        )
      ///
      REGEX_INVALID_ESCAPE = ///
        ( (?:^|[^\\]) (?:\\\\)* )        # make sure the escape isn’t escaped
        \\ (
           ?: (0[0-7])                   # octal escape
            | (x(?![\da-fA-F]{2}).{0,2}) # hex escape
            | (u\{(?![\da-fA-F]{1,}\})[^}]*\}?) # unicode code point escape
            | (u(?!\{|[\da-fA-F]{4}).{0,4}) # unicode escape
        )
      ///

      UNICODE_CODE_POINT_ESCAPE = ///
        ( \\\\ )        # make sure the escape isn’t escaped
        |
        \\u\{ ( [\da-fA-F]+ ) \}
      ///g

      LEADING_BLANK_LINE  = /^[^\n\S]*\n/
      TRAILING_BLANK_LINE = /\n[^\n\S]*$/

      TRAILING_SPACES     = /\s+$/

- ¶

  Compound assignment tokens.

      COMPOUND_ASSIGN = [
        '-=', '+=', '/=', '*=', '%=', '||=', '&&=', '?=', '<<=', '>>=', '>>>='
        '&=', '^=', '|=', '**=', '//=', '%%='
      ]

- ¶

  Unary tokens.

      UNARY = ['NEW', 'TYPEOF', 'DELETE', 'DO']

      UNARY_MATH = ['!', '~']

- ¶

  Bit-shifting tokens.

      SHIFT = ['<<', '>>', '>>>']

- ¶

  Comparison tokens.

      COMPARE = ['==', '!=', '<', '>', '<=', '>=']

- ¶

  Mathematical tokens.

      MATH = ['*', '/', '%', '//', '%%']

- ¶

  Relational tokens that are negatable with `not` prefix.

      RELATION = ['IN', 'OF', 'INSTANCEOF']

- ¶

  Boolean tokens.

      BOOL = ['TRUE', 'FALSE']

- ¶

  Tokens which could legitimately be invoked or indexed. An opening parentheses or bracket following these tokens will be recorded as the start of a function invocation or indexing operation.

      CALLABLE  = ['IDENTIFIER', 'PROPERTY', ')', ']', '?', '@', 'THIS', 'SUPER']
      INDEXABLE = CALLABLE.concat [
        'NUMBER', 'INFINITY', 'NAN', 'STRING', 'STRING_END', 'REGEX', 'REGEX_END'
        'BOOL', 'NULL', 'UNDEFINED', '}', '::'
      ]

- ¶

  Tokens which a regular expression will never immediately follow (except spaced CALLABLEs in some cases), but which a division operator can.

  See: http://www-archive.mozilla.org/js/language/js20-2002-04/rationale/syntax.html#regular-expressions

      NOT_REGEX = INDEXABLE.concat ['++', '--']

- ¶

  Tokens that, when immediately preceding a `WHEN`, indicate that the `WHEN` occurs at the start of a line. We disambiguate these from trailing whens to avoid an ambiguity in the grammar.

      LINE_BREAK = ['INDENT', 'OUTDENT', 'TERMINATOR']

- ¶

  Additional indent in front of these is ignored.

      INDENTABLE_CLOSERS = [')', '}', ']']

- ¶

  Tokens that, when appearing at the end of a line, suppress a following TERMINATOR/INDENT token

      UNFINISHED = ['\\', '.', '?.', '?::', 'UNARY', 'MATH', 'UNARY_MATH', '+', '-',
                 '**', 'SHIFT', 'RELATION', 'COMPARE', '&', '^', '|', '&&', '||',
                 'BIN?', 'THROW', 'EXTENDS', 'DEFAULT']