erl_scan
(stdlib)The Erlang Token Scanner
This module contains functions for tokenizing characters into Erlang tokens.
Types
category() = atom()
error_description() = term()
error_info() =
{erl_anno:location(), module(), error_description()}
option() =
return |
return_white_spaces |
return_comments |
text |
{reserved_word_fun, resword_fun()}
symbol() = atom() | float() | integer() | string()
resword_fun() = fun((atom()) -> boolean())
token() =
{category(), Anno :: erl_anno:anno(), symbol()} |
{category(), Anno :: erl_anno:anno()}
tokens() = [token()]
tokens_result() =
{ok, Tokens :: tokens(), EndLocation :: erl_anno:location()} |
{eof, EndLocation :: erl_anno:location()} |
{error,
ErrorInfo :: error_info(),
EndLocation :: erl_anno:location()}
Functions
string(String) -> Return
String = string()
Return =
{ok, Tokens :: tokens(), EndLocation} |
{error, ErrorInfo :: error_info(), ErrorLocation}EndLocation = ErrorLocation = erl_anno:location()
string(String, StartLocation) -> Return
String = string()
Return =
{ok, Tokens :: tokens(), EndLocation} |
{error, ErrorInfo :: error_info(), ErrorLocation}StartLocation = EndLocation = ErrorLocation = erl_anno:location()
string(String, StartLocation, Options) -> Return
String = string()
Options = options()
Return =
{ok, Tokens :: tokens(), EndLocation} |
{error, ErrorInfo :: error_info(), ErrorLocation}StartLocation = EndLocation = ErrorLocation = erl_anno:location()
Takes the list of characters
and tries to
scan (tokenize) them. Returns {ok,
,
where
are the Erlang tokens from
.
is the first location after the last token.
{error,
is returned if an error occurs.
is the first location after
the erroneous token.
string(
is equivalent to
string(
, and
string(
is equivalent to
string(
.
indicates the initial location
when scanning starts. If
is a line,
Anno
as well as
and
will be lines. If
is a pair of a line and a column
Anno
takes the form of an opaque compound
data type, and
and
will be pairs of a line and a column. The token
annotations contain information about the column and the
line where the token begins, as well as the text of the
token (if the text
option is given), all of which can
be accessed by calling
column/1,
line/1,
location/1, and
text/1.
A token is a tuple containing information about
syntactic category, the token annotations, and the actual
terminal symbol. For punctuation characters (e.g. ;
,
|
) and reserved words, the category and the symbol
coincide, and the token is represented by a two-tuple.
Three-tuples have one of the following forms: {atom,
Info, atom()}
,
{char, Info, integer()}
, {comment, Info,
string()}
, {float, Info, float()}
, {integer,
Info, integer()}
, {var, Info, atom()}
,
and {white_space, Info, string()}
.
The valid options are:
{reserved_word_fun, reserved_word_fun()}
A callback function that is called when the scanner
has found an unquoted atom. If the function returns
true
, the unquoted atom itself will be the category
of the token; if the function returns false
,
atom
will be the category of the unquoted atom.
return_comments
Return comment tokens.
return_white_spaces
Return white space tokens. By convention, if there is a newline character, it is always the first character of the text (there cannot be more than one newline in a white space token).
return
Short for [return_comments, return_white_spaces]
.
text
Include the token's text in the token annotation. The text is the part of the input corresponding to the token.
tokens(Continuation, CharSpec, StartLocation) -> Return
Continuation = return_cont() | []
CharSpec = char_spec()
StartLocation = erl_anno:location()
Return =
{done,
Result :: tokens_result(),
LeftOverChars :: char_spec()} |
{more, Continuation1 :: return_cont()}
tokens(Continuation, CharSpec, StartLocation, Options) -> Return
Continuation = return_cont() | []
CharSpec = char_spec()
StartLocation = erl_anno:location()
Options = options()
Return =
{done,
Result :: tokens_result(),
LeftOverChars :: char_spec()} |
{more, Continuation1 :: return_cont()}
char_spec() = string() | eof
return_cont()
This is the re-entrant scanner which scans characters until
a dot ('.' followed by a white space) or
eof
has been reached. It returns:
{done, Result , LeftOverChars }
This return indicates that there is sufficient input
data to get a result.
is:
{ok, Tokens, EndLocation}
The scanning was successful. Tokens
is the list of tokens including dot.
{eof, EndLocation}
End of file was encountered before any more tokens.
{error, ErrorInfo, EndLocation}
An error occurred.
is the remaining characters of the input data,
starting from EndLocation
.
{more, Continuation1 }
More data is required for building a term.
must be passed in a new call to
tokens/3,4
when more data is available.
The eof
signals end of file.
will then take the value eof
as well.
tokens(
is equivalent to
tokens(
.
See string/3 for a description of the various options.
reserved_word(Atom :: atom()) -> boolean()
Returns true
if
is an Erlang
reserved word, otherwise false
.
column(Token) -> erl_anno:column() | undefined
Token = token()
Returns the column of
's
collection of annotations.
end_location(Token) -> erl_anno:location() | undefined
Token = token()
Returns the end location of the text of
's collection of annotations. If
there is no text,
undefined
is returned.
line(Token) -> erl_anno:line()
Token = token()
Returns the line of
's collection
of annotations.
location(Token) -> erl_anno:location()
Token = token()
Returns the location of
's
collection of annotations.
text(Token) -> erl_anno:text() | undefined
Token = token()
Returns the text of
's collection
of annotations. If there is no text, undefined
is
returned.
format_error(ErrorDescriptor) -> string()
ErrorDescriptor = error_description()
Takes an
and returns
a string which
describes the error or warning. This function is usually
called implicitly when processing an ErrorInfo
structure (see below).
Error Information
The ErrorInfo
mentioned above is the standard
ErrorInfo
structure which is returned from all IO
modules. It has the following format:
{ErrorLocation, Module, ErrorDescriptor}
A string which describes the error is obtained with the following call:
Module:format_error(ErrorDescriptor)
Notes
The continuation of the first call to the re-entrant input
functions must be []
. Refer to Armstrong, Virding and
Williams, 'Concurrent Programming in Erlang', Chapter 13, for a
complete description of how the re-entrant input scheme works.