errormsg.sml

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 *)