leex(3erl) Erlang Module Definition leex(3erl)
NAME
leex - Lexical analyzer generator for Erlang
DESCRIPTION
A regular expression based lexical analyzer generator for Erlang, simi-
lar 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 de-
fault 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_warn-
ings.
{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_warn-
ings.
{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 generat-
ing 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 {ver-
bose, 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
Module:string(String) -> StringRet
Module: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 con-
sumed.
Module:token(Cont, Chars) -> {more,Cont1} | {done,TokenRet,RestChars}
Module:token(Cont, Chars, StartLine) -> {more,Cont1} | {done,Token-
Ret,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 to-
ken. 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,unicode,Prompt,Module,token,[Line]})
-> TokenRet
Module:tokens(Cont, Chars) -> {more,Cont1} | {done,TokensRet,RestChars}
Module:tokens(Cont, Chars, StartLine) -> {more,Cont1} | {done,Token-
sRet,RestChars}
Types:
Cont = [] | Cont1
Cont1 = tuple()
Chars = RestChars = string() | eof
TokensRet = {ok, Tokens, EndLine} | {eof, EndLine} | Error-
Info
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,...}. Oth-
erwise {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,unicode,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 parenthe-
ses.
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 regu-
lar expression. If <Regexp> matches then the corresponding <Erlang
code> is evaluated to generate a token. With the Erlang code the fol-
lowing 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 out-
put 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. Wein-
berger. 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.... Char-
acter 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.
Ericsson AB parsetools 2.2 leex(3erl)