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NAME

       leex - Lexical analyzer generator for Erlang

DESCRIPTION

       A regular expression based lexical analyzer generator for Erlang, similar to lex or flex.

   Note:
       The  Leex  module  should  be  considered experimental as it will be subject to changes in
       future releases.

DATA TYPES

       ErrorInfo = {ErrorLine,module(),error_descriptor()}
       ErrorLine = integer()
       Token = tuple()

EXPORTS

       file(FileName) -> LeexRet
       file(FileName, Options) -> LeexRet

              Types:

                 FileName = filename()
                 Options = Option | [Option]
                 Option = - see below -
                 LeexRet = {ok, Scannerfile} | {ok, Scannerfile,  Warnings}  |  error  |  {error,
                 Errors, Warnings}
                 Scannerfile = filename()
                 Warnings = Errors = [{filename(), [ErrorInfo]}]
                 ErrorInfo = {ErrorLine, module(), Reason}
                 ErrorLine = integer()
                 Reason = - formatable by format_error/1 -

              Generates  a lexical analyzer from the definition in the input file. The input file
              has the extension .xrl. This is added to the filename  if  it  is  not  given.  The
              resulting module is the Xrl filename without the .xrl extension.

              The current options are:

                dfa_graph:
                  Generates a .dot file which contains a description of the DFA in a format which
                  can be viewed with Graphviz, www.graphviz.com.

                {includefile,Includefile}:
                  Uses  a   specific   or   customised   prologue   file   instead   of   default
                  lib/parsetools/include/leexinc.hrl which is otherwise included.

                {report_errors, bool()}:
                  Causes errors to be printed as they occur. Default is true.

                {report_warnings, bool()}:
                  Causes warnings to be printed as they occur. Default is true.

                warnings_as_errors:
                  Causes warnings to be treated as errors.

                {report, bool()}:
                  This is a short form for both report_errors and report_warnings.

                {return_errors, bool()}:
                  If  this  flag  is  set,  {error,  Errors, Warnings} is returned when there are
                  errors. Default is false.

                {return_warnings, bool()}:
                  If this flag is set, an extra field containing Warnings is added to  the  tuple
                  returned upon success. Default is false.

                {return, bool()}:
                  This is a short form for both return_errors and return_warnings.

                {scannerfile, Scannerfile}:
                  Scannerfile  is  the name of the file that will contain the Erlang scanner code
                  that is generated. The default ("") is to add the extension  .erl  to  FileName
                  stripped of the .xrl extension.

                {verbose, bool()}:
                  Outputs  information  from  parsing  the input file and generating the internal
                  tables.

              Any of the Boolean options can be set to true by stating the name  of  the  option.
              For example, verbose is equivalent to {verbose, true}.

              Leex  will add the extension .hrl to the Includefile name and the extension .erl to
              the Scannerfile name, unless the extension is already there.

       format_error(ErrorInfo) -> Chars

              Types:

                 Chars = [char() | Chars]

              Returns a string which describes the error ErrorInfo  returned  when  there  is  an
              error in a regular expression.

GENERATED SCANNER EXPORTS

       The following functions are exported by the generated scanner.

EXPORTS

       string(String) -> StringRet
       string(String, StartLine) -> StringRet

              Types:

                 String = string()
                 StringRet = {ok,Tokens,EndLine} | ErrorInfo
                 Tokens = [Token]
                 EndLine = StartLine = integer()

              Scans String and returns all the tokens in it, or an error.

          Note:
              It is an error if not all of the characters in String are consumed.

       token(Cont, Chars) -> {more,Cont1} | {done,TokenRet,RestChars}
       token(Cont, Chars, StartLine) -> {more,Cont1} | {done,TokenRet,RestChars}

              Types:

                 Cont = [] | Cont1
                 Cont1 = tuple()
                 Chars = RestChars = string() | eof
                 TokenRet = {ok, Token, EndLine} | {eof, EndLine} | ErrorInfo
                 StartLine = EndLine = integer()

              This is a re-entrant call to try and scan one token from Chars. If there are enough
              characters in Chars to either scan a token or detect an error  then  this  will  be
              returned with {done,...}. Otherwise {cont,Cont} will be returned where Cont is used
              in the next call to token() with more characters to try an scan the token. This  is
              continued until a token has been scanned. Cont is initially [].

              It is not designed to be called directly by an application but used through the i/o
              system where it can typically be called in an application by:

              io:request(InFile, {get_until,Prompt,Module,token,[Line]})
                -> TokenRet

       tokens(Cont, Chars) -> {more,Cont1} | {done,TokensRet,RestChars}
       tokens(Cont, Chars, StartLine) -> {more,Cont1} | {done,TokensRet,RestChars}

              Types:

                 Cont = [] | Cont1
                 Cont1 = tuple()
                 Chars = RestChars = string() | eof
                 TokensRet = {ok, Tokens, EndLine} | {eof, EndLine} | ErrorInfo
                 Tokens = [Token]
                 StartLine = EndLine = integer()

              This is a re-entrant call to try and scan tokens from Chars. If  there  are  enough
              characters  in  Chars  to  either  scan tokens or detect an error then this will be
              returned with {done,...}. Otherwise {cont,Cont} will be returned where Cont is used
              in  the  next call to tokens() with more characters to try an scan the tokens. This
              is continued until all tokens have been scanned. Cont is initially [].

              This functions differs from token in that it will continue to scan tokens upto  and
              including  an  {end_token,Token}  has been scanned (see next section). It will then
              return all the tokens. This is typically used for  scanning  grammars  like  Erlang
              where  there is an explicit end token, '.'. If no end token is found then the whole
              file will be scanned and returned. If an error occurs  then  all  tokens  upto  and
              including the next end token will be skipped.

              It is not designed to be called directly by an application but used through the i/o
              system where it can typically be called in an application by:

              io:request(InFile, {get_until,Prompt,Module,tokens,[Line]})
                -> TokensRet

INPUT FILE FORMAT

       Erlang style comments starting with a % are allowed in scanner files.  A  definition  file
       has the following format:

       <Header>

       Definitions.

       <Macro Definitions>

       Rules.

       <Token Rules>

       Erlang code.

       <Erlang code>

       The  "Definitions.",  "Rules." and "Erlang code." headings are mandatory and must occur at
       the beginning of a source line.  The  <Header>,  <Macro  Definitions>  and  <Erlang  code>
       sections may be empty but there must be at least one rule.

       Macro definitions have the following format:

       NAME = VALUE

       and  there must be spaces around =. Macros can be used in the regular expressions of rules
       by writing {NAME}.

   Note:
       When macros are expanded in expressions the macro calls are replaced by  the  macro  value
       without any form of quoting or enclosing in parentheses.

       Rules have the following format:

       <Regexp> : <Erlang code>.

       The  <Regexp>  must occur at the start of a line and not include any blanks; use \t and \s
       to include TAB and SPACE characters in the regular expression. If  <Regexp>  matches  then
       the corresponding <Erlang code> is evaluated to generate a token. With the Erlang code the
       following predefined variables are available:

         TokenChars:
           A list of the characters in the matched token.

         TokenLen:
           The number of characters in the matched token.

         TokenLine:
           The line number where the token occurred.

       The code must return:

         {token,Token}:
           Return Token to the caller.

         {end_token,Token}:
           Return Token and is last token in a tokens call.

         skip_token:
           Skip this token completely.

         {error,ErrString}:
           An error in the token, ErrString is a string describing the error.

       It is also possible to push back characters into the input characters with  the  following
       returns:

         * {token,Token,PushBackList}

         * {end_token,Token,PushBackList}

         * {skip_token,PushBackList}

       These have the same meanings as the normal returns but the characters in PushBackList will
       be prepended to the input characters and scanned for the next  token.  Note  that  pushing
       back a newline will mean the line numbering will no longer be correct.

   Note:
       Pushing back characters gives you unexpected possibilities to cause the scanner to loop!

       The  following  example  would  match  a simple Erlang integer or float and return a token
       which could be sent to the Erlang parser:

       D = [0-9]

       {D}+ :
         {token,{integer,TokenLine,list_to_integer(TokenChars)}}.

       {D}+\.{D}+((E|e)(\+|\-)?{D}+)? :
         {token,{float,TokenLine,list_to_float(TokenChars)}}.

       The Erlang code in the "Erlang code." section is written into  the  output  file  directly
       after  the  module declaration and predefined exports declaration so it is possible to add
       extra exports, define imports and other attributes which are then  visible  in  the  whole
       file.

REGULAR EXPRESSIONS

       The  regular expressions allowed here is a subset of the set found in egrep and in the AWK
       programming language, as defined in the book, The AWK Programming Language, by A. V.  Aho,
       B. W. Kernighan, P. J. Weinberger. They are composed of the following characters:

         c:
           Matches the non-metacharacter c.

         \c:
           Matches the escape sequence or literal character c.

         .:
           Matches any character.

         ^:
           Matches the beginning of a string.

         $:
           Matches the end of a string.

         [abc...]:
           Character  class,  which  matches  any  of the characters abc.... Character ranges are
           specified by a pair of characters separated by a -.

         [^abc...]:
           Negated character class, which matches any character except abc....

         r1 | r2:
           Alternation. It matches either r1 or r2.

         r1r2:
           Concatenation. It matches r1 and then r2.

         r+:
           Matches one or more rs.

         r*:
           Matches zero or more rs.

         r?:
           Matches zero or one rs.

         (r):
           Grouping. It matches r.

       The escape sequences allowed are the same as for Erlang strings:

         \b:
           Backspace.

         \f:
           Form feed.

         \n:
           Newline (line feed).

         \r:
           Carriage return.

         \t:
           Tab.

         \e:
           Escape.

         \v:
           Vertical tab.

         \s:
           Space.

         \d:
           Delete.

         \ddd:
           The octal value ddd.

         \xhh:
           The hexadecimal value hh.

         \x{h...}:
           The hexadecimal value h....

         \c:
           Any other character literally, for example \\ for backslash, \" for ".

       The following examples define simplified versions of a few Erlang data types:

       Atoms [a-z][0-9a-zA-Z_]*

       Variables [A-Z_][0-9a-zA-Z_]*

       Floats (\+|-)?[0-9]+\.[0-9]+((E|e)(\+|-)?[0-9]+)?

   Note:
       Anchoring a regular expression with ^ and $ is not implemented in the current  version  of
       Leex and just generates a parse error.