(* Some important character-based functions for text-processing *)

fun isASCII (n) = ((0 <= n) andalso (n <= 255));

fun isSp (ch) = (ch = #" ");

fun isLf (ch) = (ch = #"\n");

fun isTab (ch) = (ch = #"\t");

fun isWhite (ch) = isSp (ch) orelse isLf (ch) orelse isTab(ch);

fun isDigit (ch) = ((ch >= #"0") andalso (ch <= #"9"));

fun isUpper (ch) = ((ch >= #"A") andalso (ch <= #"Z"));

fun isLower (ch) = ((ch >= #"a") andalso (ch <= #"z"));

fun isAlpha (ch) = isUpper (ch) orelse isLower (ch);

fun isAlphaNum (ch) = isAlpha (ch) orelse isDigit (ch);

val zero = ord (#"0");

fun digitValue (ch) =
    let exception BadDigit
    in  if isDigit (ch) then ord(ch) - zero
        else raise BadDigit
    end
;

fun lower2Upper (ch) =
    if ((#"a" <= ch) andalso (ch <= #"z")) then chr(ord(ch) - 32)
    else ch
;

fun upper2Lower (ch) =
    if ((#"A" <= ch) andalso (ch <= #"Z")) then chr(ord(ch) + 32)
    else ch
;

(* Given a function f: char -> char, the following function lifts f to a
   corresponding function : string -> string
*)

fun mapstring (f) =
    let fun G (s) = implode ((map f) (explode (s)))
    in  G
    end
;

(* Given a function f: char -> char list, the following function lifts f to a
   corresponding function : string -> char list list
*)

fun mapstr2chlstlst (f) =
    let fun G (s) = (map f) (explode (s))
    in  G
    end
;