INTERFACE CharRange;
TYPE
  T = SET OF CHAR;
CONST
  NoChars = T{};
  AllChars = T {FIRST(CHAR) .. LAST(CHAR)};
  AllExceptNewline = AllChars - T{'\n'};
  WhiteSpace = T{' ','\t'};
  Letter = T{'A'..'Z','a'..'z','_'};
  Digit = T{'0'..'9'};
  AlphaNum = Letter + Digit;

PROCEDURE FromText(t: TEXT): T;

PROCEDURE FilterText(t: TEXT;
                     replace: T := WhiteSpace;
                     with: CHAR := '\000'): TEXT;
  (* '\000' means delete *)

PROCEDURE Size(a: T): INTEGER;

number of chars in the set

END CharRange.