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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 Information).
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:location()
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 ErrorLocation 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 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 option text is specified), 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 terminal symbol. For punctuation 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 character, if present, 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 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 either 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 result. 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 characters 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 Programming in Erlang', Chapter 13.
SEE ALSO
erl_anno(3erl), erl_parse(3erl), io(3erl)