APL grammar - tokens

token character_constant_double {
    (") <double_quoted_character>* "   
}

token character_constant_single {
    (') <single_quoted_character>* '
}

token single_quoted_character { '' | <-[']> }

token double_quoted_character { "" | <-["]> }

token variable_identifier { <[A..Za..z]> \w* }