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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,
Warnings, Errors}
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 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.