Errors.m: Use a new faster backtrace implementation and enable it by …

…default

Tools/MathematicaMisc/Errors.m

@@ -22,7 +22,7 @@
 CatchKrancError;
 ReportFunctionCounts;
 
-$EnableBacktrace = False;
+$EnableBacktrace = True;
 
 Begin["`Private`"];
 
@@ -70,8 +70,7 @@
 compatibility, it can be called with several arguments.  These will be
 converted to strings in InputForm and displayed on separate lines. *)
 ThrowError[objects__] :=
-  Module[{stack = CurrentStack[]},
-    Throw[KrancError[{objects},stack], KrancError]];
+  Throw[KrancError[{objects},StackRead[$stack]], KrancError];
 
 VerifyString[s_] := 
   If[! StringQ[s],
@@ -108,29 +107,31 @@
 incrementCount[fn_] :=
   count[fn] = count[fn]+1;
 
-Print[$EnableBacktrace];
+$stack = {};
 
-If[$EnableBacktrace, 
-DefFn[def:(fn_[args___] := body_)] :=
-  Module[
-    {},
+If[$EnableBacktrace,
+  DefFn[def:(fn_[args___] := body_)] :=
+  Module[{},
     ErrorDefinition[fn];
     fn[args] :=
-    (incrementCount[fn];WithStackFrame[fn, body])],
-(* else *)
-DefFn[def:(fn_[args___] := body_)] :=
-  Module[
-    {},
+    (* This construction using Part avoids introducing an explicit
+       temporary with Module which causes a big performance hit. *)
+    (incrementCount[fn]; {StackPush[$stack,fn], Catch[body,_, (StackPop[$stack]; Throw[#1,#2]) &], StackPop[$stack]}[[2]])],
+
+  (* else *)
+
+  DefFn[def:(fn_[args___] := body_)] :=
+  Module[{},
     ErrorDefinition[fn];
     fn[args] :=
-    (incrementCount[fn];body)]];
+    (incrementCount[fn]; body)]];
 
 reportError[k:KrancError[objects_,stack_], KrancError] :=
   Module[{},
     If[MatchQ[objects, {_String}],
       Print["Error: ", objects[[1]]],
       Scan[Print, InputForm/@objects]];
-    If[$EnableBacktrace, ShowStack[stack]];
+    If[$EnableBacktrace, Print["in ", Sequence@@Riffle[stack,"/"]]];
     $Failed];
 
 SetAttributes[CatchKrancError, HoldAll];