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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)