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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, [, 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.