scanner

    //Note: scanners don't use stack and node, just read/look and keep/noKeep.
    attribute defaults "noStack" "read" "noNode" "keep".

    output "All". //One of All, Smalltalk, Ruby, C++, C++98, JavaList, or Java.

    uppercase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".
    lowercase = "abcdefghijklmnopqrstuvwxyz".
    letter = uppercase | lowercase | "_".
    digit = "0123456789".
    operator = "+-*/<>=".

    tab = 9 [noKeep].
    carriageReturn = 13 [noKeep].
    lineFeed = 10 [noKeep].
    formFeed = 12 [noKeep].
    blank = 32 [noKeep]. 

    lineEnd = carriageReturn | lineFeed  | formFeed.
    space = blank | tab | lineEnd.
    others = "?[]{}()^;#:.$_" | singleQuote | doubleQuote | space.

    printable = letter | digit | operator | others .
    endOfFileCharacter = 256.
    all = printable | endOfFileCharacter.

    EndOfFile {endOfFileCharacter}
        -> => '-|'.

    WhiteSpace {all - space}
       -> space+.

    Identifier {all - (letter | digit | $_)}
        -> letter (letter | digit | $_ )* => 'walkIdentifier:' .

    Operator1 {all}
        -> $+ => '+' 
        -> $- => '-' 
        -> $* => '*' 
        -> $/ => '/' 
	-> $= $= => '=='
	-> $< => '<'
	-> $> => '>' .

    Operator2 {all - $=}
	-> $= => '='.

    Punctuation {all}
	-> $, => ',' 
	-> $; => ';' 
	-> $? => '?' 
	-> $: => ':' .

    Brackets {all}
        -> $( => '(' 
        -> $) => ')' 
        -> ${ => '{' 
        -> $} => '}' .


    Number {all - digit}
        -> digit+ => 'walkInteger:' .

    Comment {all}
	-> $# [noKeep] ((all - lineEnd) [noKeep])* lineEnd [noKeep] .

    //An example that uses keep and noKeep.
    //DoubleQuotedStringOrSymbol {all - $"}
    //    -> $" [noKeep] 
    //        ((printable - $") [keep] | $" [noKeep] $" [keep])* 
    //       $" [noKeep] => DoubleQuotedString
    //    -> $" [noKeep] 
    //        ((printable - $") [keep] | $" [noKeep] $" [keep])* 
    //       {endOfFileCharacter} #syntaxError: ["missing end quote for double quoted string"] => DoubleQuotedString