Errors.m: Add DefFn function for defining functions

This means that ErrorDefinition can be applied automatically.  In future we could add profiling and stack information for backtraces.

Tools/MathematicaMisc/Errors.m

@@ -16,6 +16,7 @@
 Terse = 2;
 Info = 3;
 InfoFull = 4;
+DefFn;
 
 Begin["`Private`"];
 
@@ -93,6 +94,14 @@
   x[args___] :=
     ThrowError["Invalid arguments to "<>ToString[x], {args}//FullForm];
 
+SetAttributes[DefFn, HoldAll];
+
+DefFn[def:(fn_[args___] := body_)] :=
+  Module[
+    {},
+    ErrorDefinition[fn];
+    def];   
+
 End[];
 
 EndPackage[];