Add the tiger source code bundle from the book site

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

tiger/chap3/errormsg.sml

@@ -0,0 +1,53 @@
+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 *)
+