APL grammar - tokens

token constant {
      <character_constant_double>
    | <character_constant_single>
    | <numeric_constant>
}

token numeric_constant { 
    <decimal_representation> [ \s+ <decimal_representation> ]*
}

token decimal_representation {
    [ ⁻? \d+ \.? \d* | ⁻? \. \d+ ] [ E ⁻? \d+ ]?
}