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NAME
erl_scan - The Erlang Token Scanner
DESCRIPTION
This module contains functions for tokenizing characters into Erlang tokens.
DATA TYPES
attribute_info() = {column, column()}
| {length, integer() >= 1}
| {line, info_line()}
| {location, info_location()}
| {text, string()}
attributes() = line() | attributes_data()
attributes_data() = [{column, column()} |
{line, info_line()} |
{text, string()}]
| {line(), column()}
category() = atom()
column() = integer() >= 1
error_description() = term()
error_info() = {location(), module(), error_description()}
info_line() = integer() | term()
info_location() = location() | term()
line() = integer()
location() = line() | {line(), column()}
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(), attributes(), symbol()}
| {category(), attributes()}
token_info() = {category, category()}
| {symbol, symbol()}
| attribute_info()
tokens() = [token()]
tokens_result() = {ok,
Tokens :: tokens(),
EndLocation :: location()}
| {eof, EndLocation :: location()}
| {error,
ErrorInfo :: error_info(),
EndLocation :: location()}
EXPORTS
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 = location()
Takes the list of characters String and tries to scan (tokenize) them. Returns {ok, Tokens,
EndLocation}, where Tokens are the Erlang tokens from String. EndLocation is the first location
after the last token.
{error, ErrorInfo, ErrorLocation} is returned if an error occurs. 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
attributes() as well as EndLocation and ErrorLocation will be lines. If StartLocation is a pair of
a line and a column attributes() takes the form of an opaque compound data type, and EndLocation
and ErrorLocation will be pairs of a line and a column. The token attributes 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 token_info/1,2 or
attributes_info/1,2.
A token is a tuple containing information about syntactic category, the token attributes, 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 attributes. The text is the part of the input
corresponding to the token.
tokens(Continuation, CharSpec, StartLocation) -> Return
tokens(Continuation, CharSpec, StartLocation, Options) -> Return
Types:
Continuation = return_cont() | []
CharSpec = char_spec()
StartLocation = 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 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. 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 will then take the value eof as well.
tokens(Continuation, CharSpec, StartLocation) is equivalent to tokens(Continuation, CharSpec,
StartLocation, []).
See string/3 for a description of the various options.
reserved_word(Atom :: atom()) -> boolean()
Returns true if Atom is an Erlang reserved word, otherwise false.
token_info(Token) -> TokenInfo
Types:
Token = token()
TokenInfo = [TokenInfoTuple :: token_info()]
Returns a list containing information about the token Token. The order of the TokenInfoTuples is
not defined. See token_info/2 for information about specific TokenInfoTuples.
Note that if token_info(Token, TokenItem) returns undefined for some TokenItem, the item is not
included in TokenInfo.
token_info(Token, TokenItem) -> TokenInfoTuple | undefined
token_info(Token, TokenItems) -> TokenInfo
Types:
Token = token()
TokenItems = [TokenItem :: token_item()]
TokenInfo = [TokenInfoTuple :: token_info()]
token_item() = category | symbol | attribute_item()
attribute_item() = column | length | line | location | text
Returns a list containing information about the token Token. If one single TokenItem is given the
returned value is the corresponding TokenInfoTuple, or undefined if the TokenItem has no value. If
a list of TokenItems is given the result is a list of TokenInfoTuple. The TokenInfoTuples will
appear with the corresponding TokenItems in the same order as the TokenItems appear in the list of
TokenItems. TokenItems with no value are not included in the list of TokenInfoTuple.
The following TokenInfoTuples with corresponding TokenItems are valid:
{category, category()}:
The category of the token.
{column, column()}:
The column where the token begins.
{length, integer() > 0}:
The length of the token's text.
{line, line()}:
The line where the token begins.
{location, location()}:
The line and column where the token begins, or just the line if the column unknown.
{symbol, symbol()}:
The token's symbol.
{text, string()}:
The token's text.
attributes_info(Attributes) -> AttributesInfo
Types:
Attributes = attributes()
AttributesInfo = [AttributeInfoTuple :: attribute_info()]
Returns a list containing information about the token attributes Attributes. The order of the
AttributeInfoTuples is not defined. See attributes_info/2 for information about specific
AttributeInfoTuples.
Note that if attributes_info(Token, AttributeItem) returns undefined for some AttributeItem in the
list above, the item is not included in AttributesInfo.
attributes_info(Attributes, AttributeItem) ->
AttributeInfoTuple | undefined
attributes_info(Attributes, AttributeItems) -> AttributeInfo
Types:
Attributes = attributes()
AttributeItems = [AttributeItem :: attribute_item()]
AttributeInfo = [AttributeInfoTuple :: attribute_info()]
attribute_item() = column | length | line | location | text
Returns a list containing information about the token attributes Attributes. If one single
AttributeItem is given the returned value is the corresponding AttributeInfoTuple, or undefined if
the AttributeItem has no value. If a list of AttributeItem is given the result is a list of
AttributeInfoTuple. The AttributeInfoTuples will appear with the corresponding AttributeItems in
the same order as the AttributeItems appear in the list of AttributeItems. AttributeItems with no
value are not included in the list of AttributeInfoTuple.
The following AttributeInfoTuples with corresponding AttributeItems are valid:
{column, column()}:
The column where the token begins.
{length, integer() > 0}:
The length of the token's text.
{line, line()}:
The line where the token begins.
{location, location()}:
The line and column where the token begins, or just the line if the column unknown.
{text, string()}:
The token's text.
set_attribute(AttributeItem, Attributes, SetAttributeFun) ->
Attributes
Types:
AttributeItem = line
Attributes = attributes()
SetAttributeFun = fun((info_line()) -> info_line())
Sets the value of the line attribute of the token attributes Attributes.
The SetAttributeFun is called with the value of the line attribute, and is to return the new value
of the line attribute.
format_error(ErrorDescriptor) -> string()
Types:
ErrorDescriptor = error_description()
Takes an ErrorDescriptor 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.
SEE ALSO
io(3erl), erl_parse(3erl)