# erl_scan

### MODULE

erl_scan

### MODULE SUMMARY

The Erlang Token Scanner

### DESCRIPTION

This module contains functions for tokenizing characters into Erlang tokens.

### EXPORTS

string(CharList,StartLine]) -> {ok, Tokens, EndLine} | Error
string(CharList) -> {ok, Tokens, EndLine} | Error

Types:

CharList = string()
StartLine = EndLine = Line = integer()
Tokens = [{atom(),Line}|{atom(),Line,term()}]
Error = {error, ErrorInfo, EndLine}

Takes the list of characters CharList and tries to scan (tokenize) them. Returns {ok, Tokens, EndLine}, where Tokens are the Erlang tokens from CharList. EndLine is the last line where a token was found.

StartLine indicates the initial line when scanning starts. string/1 is equivalent to string(CharList,1).

{error, ErrorInfo, EndLine} is returned if an error occurs. EndLine indicates where the error occurred.

tokens(Continuation, CharList, StartLine) ->Return

Types:

Return = {done, Result, LeftOverChars} | {more, Continuation}
Continuation = [] | string()
CharList = string()
StartLine = EndLine = integer()
Result = {ok, Tokens, EndLine} | {eof, EndLine}
Tokens = [{atom(),Line}|{atom(),Line,term()}]

This is the re-entrant scanner which scans characters until a dot ('.' whitespace) has been reached. It returns:

{done, Result, LeftOverChars}
  This return indicates that there is sufficient input data to get an input. Result is:
  {ok, Tokens, EndLine}
    The scanning was successful. Tokens is the list of tokens including dot.
  {eof, EndLine}
    End of file was encountered before any more tokens.
  {error, ErrorInfo, EndLine}
    An error occurred.
{more, Continuation}
  More data is required for building a term. Continuation must be passed in a new call to tokens/3 when more data is available.

reserved_word(Atom) -> bool()

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

format_error(ErrorDescriptor) -> string()

Types:

ErrorDescriptor = errordesc()

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:

        {ErrorLine, Module, ErrorDescriptor}

A string which describes the error is obtained with the following call:

    apply(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(3), erl_parse(3)

stdlib 1.15.3
Copyright © 1991-2008 Ericsson AB