GHCi debugger: new flag -fbreak-on-exception

When -fbreak-on-exception is set, an exception will cause GHCi to
suspend the current computation and return to the prompt, where the
history of the current evaluation can be inspected (if we are in
:trace).  This isn't on by default, because the behaviour could be
confusing: for example, ^C will cause a breakpoint.  It can be very
useful for finding the cause of a "head []" or a "fromJust Nothing",
though.

1 files changed, 16 insertions, 23 deletions

diff --git a/rts/Interpreter.c b/rts/Interpreter.c
index fbbda9d14f..6663445995 100644
--- a/rts/Interpreter.c
+++ b/rts/Interpreter.c
@@ -16,6 +16,7 @@
 #include "Updates.h"
 #include "Sanity.h"
 #include "Liveness.h"
+#include "Prelude.h"
 
 #include "Bytecodes.h"
 #include "Printer.h"
@@ -83,7 +84,8 @@ allocate_NONUPD (int n_words)
     return allocate(stg_max(sizeofW(StgHeader)+MIN_PAYLOAD_SIZE, n_words));
 }
 
-rtsBool stop_next_breakpoint = rtsFalse;
+int rts_stop_next_breakpoint = 0;
+int rts_stop_on_exception = 0;
 
 #ifdef INTERP_STATS
 
@@ -177,7 +179,7 @@ static StgWord app_ptrs_itbl[] = {
     (W_)&stg_ap_pppppp_info,
 };
 
-HsStablePtr breakPointIOAction; // points to the IO action which is executed on a breakpoint
+HsStablePtr rts_breakpoint_io_action; // points to the IO action which is executed on a breakpoint
                                 // it is set in main/GHC.hs:runStmt
 
 Capability *
@@ -809,15 +811,15 @@ run_BCO:
                breakPoints = (StgArrWords *) BCO_PTR(arg1_brk_array);
 
                // stop the current thread if either the
-               // "stop_next_breakpoint" flag is true OR if the
+               // "rts_stop_next_breakpoint" flag is true OR if the
                // breakpoint flag for this particular expression is
                // true
-               if (stop_next_breakpoint == rtsTrue || 
+               if (rts_stop_next_breakpoint == rtsTrue || 
                    breakPoints->payload[arg2_array_index] == rtsTrue)
                {
                   // make sure we don't automatically stop at the
                   // next breakpoint
-                  stop_next_breakpoint = rtsFalse;
+                  rts_stop_next_breakpoint = rtsFalse;
 
                   // allocate memory for a new AP_STACK, enough to
                   // store the top stack frame plus an
@@ -840,16 +842,17 @@ run_BCO:
                   }
 
                   // prepare the stack so that we can call the
-                  // breakPointIOAction and ensure that the stack is
+                  // rts_breakpoint_io_action and ensure that the stack is
                   // in a reasonable state for the GC and so that
                   // execution of this BCO can continue when we resume
-                  ioAction = (StgClosure *) deRefStablePtr (breakPointIOAction);
-                  Sp -= 7;
-                  Sp[6] = (W_)obj;   
-                  Sp[5] = (W_)&stg_apply_interp_info;
-                  Sp[4] = (W_)new_aps;                 // the AP_STACK
-                  Sp[3] = (W_)BCO_PTR(arg3_freeVars);  // the info about local vars of the breakpoint
-                  Sp[2] = (W_)&stg_ap_ppv_info;
+                  ioAction = (StgClosure *) deRefStablePtr (rts_breakpoint_io_action);
+                  Sp -= 8;
+                  Sp[7] = (W_)obj;   
+                  Sp[6] = (W_)&stg_apply_interp_info;
+                  Sp[5] = (W_)new_aps;                 // the AP_STACK
+                  Sp[4] = (W_)BCO_PTR(arg3_freeVars);  // the info about local vars of the breakpoint
+                  Sp[3] = (W_)False_closure;            // True <=> a breakpoint
+                  Sp[2] = (W_)&stg_ap_pppv_info;
                   Sp[1] = (W_)ioAction;                // apply the IO action to its two arguments above
                   Sp[0] = (W_)&stg_enter_info;         // get ready to run the IO action
 
@@ -1374,13 +1377,3 @@ run_BCO:
 
     barf("interpretBCO: fell off end of the interpreter");
 }
-
-/* set the single step flag for the debugger to True -
-   it gets set back to false in the interpreter everytime
-   we hit a breakpoint
-*/
-void rts_setStepFlag (void);
-void rts_setStepFlag (void)
-{
-   stop_next_breakpoint = rtsTrue;
-}