errormsg.sml

(*******************************************************************************
 * File:        errormsg.sml
 * Authors:     (starter code)
 *
 * Description: Provides support for error reporting with information about
 *              the context of the error that occurred.
 ******************************************************************************)

signature ERRORMSG =
sig
  val anyErrors : bool ref
  val fileName : string ref
  val lineNum : int ref
  val linePos : int list ref
  val sourceStream : TextIO.instream ref
  val error : int -> string -> unit

  exception Error

  val impossible : string -> 'a   (* raises Error *)
  val reset : unit -> unit
end

structure ErrorMsg : ERRORMSG =
struct
  val anyErrors = ref false
  val fileName = ref ""
  val lineNum = ref 1
  val linePos = ref [1]
  val sourceStream = ref TextIO.stdIn

  fun reset () =
    (anyErrors    := false;
     fileName     := "";
     lineNum      := 1;
     linePos      := [1];
     sourceStream := TextIO.stdIn)

  exception Error

  fun error pos (msg:string) =
    let fun look (a::rest,n) =
              if a < pos then
                app print [":",
                           Int.toString n,
                           ".",
                           Int.toString (pos - a)]
              else
                look (rest, n - 1)
          | look _ = print "0.0"

    in  anyErrors := true;

        print (!fileName);

        look (!linePos, !lineNum);

        print ":";
        print msg;
        print "\n"
    end

  fun impossible msg =
    (app print ["Error: Compiler bug: ", msg, "\n"];
     TextIO.flushOut TextIO.stdOut;
     raise Error)

end  (* structure ErrorMsg *)
(* nice *)