erl_scan(3erl) Erlang Module Definition erl_scan(3erl)
NAME
erl_scan - The Erlang token scanner.
DESCRIPTION
This module contains functions for tokenizing (scanning) characters
into Erlang tokens.
DATA 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()}
options() = option() | [option()]
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()}
EXPORTS
category(Token) -> category()
Types:
Token = token()
Returns the category of Token.
column(Token) -> erl_anno:column() | undefined
Types:
Token = token()
Returns the column of Token's collection of annotations.
end_location(Token) -> erl_anno:location() | undefined
Types:
Token = token()
Returns the end location of the text of Token's collection of
annotations. If there is no text, undefined is returned.
format_error(ErrorDescriptor) -> string()
Types:
ErrorDescriptor = error_description()
Uses an ErrorDescriptor and returns a string that describes the
error or warning. This function is usually called implicitly
when an ErrorInfo structure is processed (see section Error In-
formation).
line(Token) -> erl_anno:line()
Types:
Token = token()
Returns the line of Token's collection of annotations.
location(Token) -> erl_anno:location()
Types:
Token = token()
Returns the location of Token's collection of annotations.
reserved_word(Atom :: atom()) -> boolean()
Returns true if Atom is an Erlang reserved word, otherwise
false.
string(String) -> Return
string(String, StartLocation) -> Return
string(String, StartLocation, Options) -> Return
Types:
String = string()
Options = options()
Return =
{ok, Tokens :: tokens(), EndLocation} |
{error, ErrorInfo :: error_info(), ErrorLocation}
StartLocation = EndLocation = ErrorLocation = erl_anno:loca-
tion()
Takes the list of characters String and tries to scan (tokenize)
them. Returns one of the following:
{ok, Tokens, EndLocation}:
Tokens are the Erlang tokens from String. EndLocation is the
first location after the last token.
{error, ErrorInfo, ErrorLocation}:
An error occurred. ErrorLocation is the first location after
the erroneous token.
string(String) is equivalent to string(String, 1), and
string(String, StartLocation) is equivalent to string(String,
StartLocation, []).
StartLocation indicates the initial location when scanning
starts. If StartLocation is a line, Anno, EndLocation, and Er-
rorLocation are lines. If StartLocation is a pair of a line and
a column, Anno takes the form of an opaque compound data type,
and EndLocation and ErrorLocation are pairs of a line and a col-
umn. The token annotations contain information about the column
and the line where the token begins, as well as the text of the
token (if option text is specified), all of which can be ac-
cessed by calling column/1, line/1, location/1, and text/1.
A token is a tuple containing information about syntactic cate-
gory, the token annotations, and the terminal symbol. For punc-
tuation characters (such as ; and |) 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, Anno, atom()}
* {char, Anno, char()}
* {comment, Anno, string()}
* {float, Anno, float()}
* {integer, Anno, integer()}
* {var, Anno, atom()}
* {white_space, Anno, string()}
Valid options:
{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 becomes the category of the token. If
the function returns false, atom becomes the category of the
unquoted atom.
return_comments:
Return comment tokens.
return_white_spaces:
Return white space tokens. By convention, a newline charac-
ter, if present, is always the first character of the text
(there cannot be more than one newline in a white space to-
ken).
return:
Short for [return_comments, return_white_spaces].
text:
Include the token text in the token annotation. The text is
the part of the input corresponding to the token.
symbol(Token) -> symbol()
Types:
Token = token()
Returns the symbol of Token.
text(Token) -> erl_anno:text() | undefined
Types:
Token = token()
Returns the text of Token's collection of annotations. If there
is no text, undefined is returned.
tokens(Continuation, CharSpec, StartLocation) -> Return
tokens(Continuation, CharSpec, StartLocation, Options) -> Return
Types:
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()
An opaque continuation.
This is the re-entrant scanner, which scans characters until ei-
ther a dot ('.' followed by a white space) or eof is reached. It
returns:
{done, Result, LeftOverChars}:
Indicates that there is sufficient input data to get a re-
sult. 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. LeftOverChars is the remaining charac-
ters of the input data, starting from EndLocation.
{more, Continuation1}:
More data is required for building a term. Continuation1
must be passed in a new call to tokens/3,4 when more data is
available.
The CharSpec eof signals end of file. LeftOverChars then takes
the value eof as well.
tokens(Continuation, CharSpec, StartLocation) is equivalent to
tokens(Continuation, CharSpec, StartLocation, []).
For a description of the options, see string/3.
ERROR INFORMATION
ErrorInfo is the standard ErrorInfo structure that is returned from all
I/O modules. The format is as follows:
{ErrorLocation, Module, ErrorDescriptor}
A string describing 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 []. For a complete description of how the re-entrant input
scheme works, see Armstrong, Virding and Williams: 'Concurrent Program-
ming in Erlang', Chapter 13.
SEE ALSO
erl_anno(3erl), erl_parse(3erl), io(3erl)
Ericsson AB stdlib 3.13 erl_scan(3erl)