erl_scan

19962016 Ericsson AB. All Rights Reserved. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. erl_scan Robert Virding Bjarne Däcker 1 Bjarne Däcker 1997-01-24 B erl_scan.xml

erl_scan The Erlang token scanner.

This module contains functions for tokenizing (scanning) characters into Erlang tokens.

Return the category.

Returns the category of Token.

Return the column.

Returns the column of Token's collection of annotations.

Return the end location of the text.

Returns the end location of the text of Token's collection of annotations. If there is no text, undefined is returned.

Format an error descriptor.

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).

Return the line.

Returns the line of Token's collection of annotations.

Return the location.

Returns the location of Token's collection of annotations.

Test for a reserved word.

Returns true if Atom is an Erlang reserved word, otherwise false.

Scan a string and return the Erlang tokens.

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.

Return the symbol.

Returns the symbol of Token.

Return the text.

Returns the text of Token's collection of annotations. If there is no text, undefined is returned.

Re-entrant scanner. 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.