(* File: GRSCN.ML *)

(* Project: GR *)

datatype token
  = Key  of string
  | Name of string
  ;

exception ScanError of string;

fun is_uppercase c =
      c >= "A"  andalso  c <= "Z";

fun is_lowercase c =
      c >= "a"  andalso  c <= "z";

fun is_letter c =
      is_uppercase c  orelse  is_lowercase c;

fun is_digit c =
      c >= "0"  andalso  c <= "9";

fun read_line s =
  let fun loop cs =
        let val c = input(s,1)
        in if end_of_stream s then
             rev cs
           else if c = "\n" then
             rev ("\n"::cs)
           else
             loop (c::cs)
        end
  in loop [] end;

fun is_blank c =
  c = " "  orelse  c = "\n"  orelse  c = "\t";

fun read_and_scan file_name =
  let val s = open_in file_name
      fun scan_token [] =
            if end_of_stream s then 
              (Key "eof", [])
            else
              scan_token (read_line s)
        | scan_token ("/"::"*"::rest) =
            scan_comment rest
        | scan_token ("%"::"%"::rest) =
            (Key "%%", rest)
        | scan_token ("%"::"t"::"o"::"k"::"e"::"n"::rest) =
            (Key "%token", rest)
        | scan_token (c::rest) =
            if is_blank c then 
              scan_token rest
            else if is_letter c then 
              scan_id_rest (c, rest)
            else
              (Key c, rest)
      and scan_comment ("*"::"/"::rest) =
            scan_token rest
        | scan_comment [] =
            if end_of_stream s then
              raise ScanError "EOF in a comment"
            else
              scan_comment (read_line s)
        | scan_comment (c::rest) =
            scan_comment rest
      and scan_id_rest (ide, rest as c::rest') =
            if (is_letter c) orelse (is_digit c) orelse (c = "_") then
              scan_id_rest (ide^c, rest')
            else
              (Name ide, rest)
      fun loop (line, tks) =
            let val (tk, line') = scan_token line
            in case tk
                 of Key "eof" => rev (tk::tks)
                  | _ => loop (line', tk::tks)
            end
      val tks = loop ([], [])
      val ()  = close_in s
  in tks end;