leex(3)

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 was considered experimental when it was introduced.

  Default Leex Options

The (host operating system) environment variable ERL_COMPILER_OPTIONS can be used to give default Leex options. Its value must be a valid Erlang term. If the value is a list, it is used as is. If it is not a list, it is put into a list.

The list is appended to any options given to file/2.

The list can be retrieved with compile:env_compiler_options/0.

  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 start at the beginning of a source line. The <Header>, <Macro Definitions>, and <Erlang code> sections are allowed to 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.
TokenCol
    The column number where the token occurred (column of the first character included in the token).
TokenLoc
    Token location. Expands to {TokenLine,TokenCol} (even when error_location is set to line).

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, making it possible to add extra exports, define imports, and other attributes, which are 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, and P. J. Weinberger. They are composed of the following characters: c
    Matches the non-metacharacter 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:
    Backspace.
    Form feed.
    Newline (line feed).
    Carriage return.
    Tab.
\
    Escape.
    Vertical tab.
    Space.
    Delete.
dd
    The octal value ddd.
    The hexadecimal value hh.
    The hexadecimal value h....
    Any other character literally, for example \` for backslash, " for ".

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

    Atoms a-z*
    Variables A-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 generates a parse error.

DATA TYPES

error_info() :: {erl_anno:line() | none, module(), ErrorDescriptor :: term()}.

    The standard error_info/0 structure that is returned from all I/O modules. ErrorDescriptor is formattable by format_error/1.
error_ret() :: error | {error, Errors :: errors(), Warnings :: warnings()}.
errors() :: [{file:filename(), [error_info()]}].
leex_ret() :: ok_ret() | error_ret().
ok_ret() :: {ok, Scannerfile :: file:filename()} | {ok, Scannerfile :: file:filename(), warnings()}.
warnings() :: [{file:filename(), [error_info()]}].

FUNCTIONS

file(FileName, Options) -> leex_ret() when FileName :: file:filename(), Options :: Option | [Option], Option :: {dfa_graph, boolean()} | {includefile, Includefile :: file:filename()} | {report_errors, boolean()} | {report_warnings, boolean()} | {report, boolean()} | {return_errors, boolean()} | {return_warnings, boolean()} | {return, boolean()} | {scannerfile, Scannerfile :: file:filename()} | {verbose, boolean()} | {warnings_as_errors, boolean()} | {deterministic, boolean()} | {error_location, line | column} | {tab_size, pos_integer()} | dfa_graph | report_errors | report_warnings | report | return_errors | return_warnings | return | verbose | warnings_as_errors.

    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, boolean()}
        Causes errors to be printed as they occur. Default is true.
    {report_warnings, boolean()}
        Causes warnings to be printed as they occur. Default is true.
    {report, boolean()}
        This is a short form for both report_errors and report_warnings.
    {return_errors, boolean()}
        If this flag is set, {error, Errors, Warnings} is returned when there are errors. Default is false.
    {return_warnings, boolean()}
        If this flag is set, an extra field containing Warnings is added to the tuple returned upon success. Default is false.
    {return, boolean()}
        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, boolean()}
        Outputs information from parsing the input file and generating the internal tables.
    {warnings_as_errors, boolean()}
        Causes warnings to be treated as errors.
    {deterministic, boolean()}
        Causes generated -file() attributes to only include the basename of the file path.
    {error_location, line | column}
        If set to column, error location will be {Line,Column} tuple instead of just Line. Also, StartLoc and EndLoc in string/2, token/3, and tokens/3 functions will be {Line,Column} tuple instead of just Line. Default is line. Note that you can use TokenLoc for token location independently, even if the error_location is set to line.

        Unicode characters are counted as many columns as they use bytes to represent.
    {tab_size, pos_integer()}
        Sets the width of \t character (only relevant if error_location is set to column). Default is 8.

    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(ErrorDescriptor) -> io_lib:chars() when ErrorDescriptor :: term().

    Returns a descriptive string in English of an error reason ErrorDescriptor returned by leex:file/1,2 when there is an error in a regular expression.
string(String, StartLoc) -> StringRet when String :: string(), StringRet :: {ok, Tokens, EndLoc} | ErrorInfo, Tokens :: [Token], Token :: term(), ErrorInfo :: {error, error_info(), erl_anno:location()}, StartLoc :: erl_anno:location(), EndLoc :: erl_anno:location().

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

    StartLoc and EndLoc are either erl_anno:line() or erl_anno:location(), depending on the error_location option.

    NOTE: It is an error if not all of the characters in String are consumed.
token(Cont, Chars, StartLoc) -> {more, Cont1} | {done, TokenRet, RestChars} when Cont :: [] | Cont1, Cont1 :: tuple(), Chars :: string() | eof, RestChars :: string() | eof, TokenRet :: {ok, Token, EndLoc} | {eof, EndLoc} | ErrorInfo, ErrorInfo :: {error, error_info(), erl_anno:location()}, Token :: term(), StartLoc :: erl_anno:location(), EndLoc :: erl_anno:location().

    This is a re-entrant call to try and scan a single 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 {more,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 is used through the I/O system where it can typically be called in an application by:

        io:request(InFile, {get_until,unicode,Prompt,Module,token,[Loc]})
          -> TokenRet
tokens(Cont, Chars, StartLoc) -> {more, Cont1} | {done, TokensRet, RestChars} when Cont :: [] | Cont1, Cont1 :: tuple(), Chars :: string() | eof, RestChars :: string() | eof, TokensRet :: {ok, Tokens, EndLoc} | {eof, EndLoc} | ErrorInfo, Tokens :: [Token], Token :: term(), ErrorInfo :: {error, error_info(), erl_anno:location()}, StartLoc :: erl_anno:location(), EndLoc :: erl_anno:location().

    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 {more,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 up to 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 up to 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,unicode,Prompt,Module,tokens,[Loc]})
          -> TokensRet