[Enhancement] add experimental error handling: Fiber.try() and built-in raise()

scripts/run_tests.py

@@ -28,8 +28,9 @@
     "lang/fibers.pk",
     "lang/functions.pk",
     "lang/import.pk",
+    "lang/try.pk",
   ),
-  
+
   "Modules Test" : (
     "modules/dummy.pk",
     "modules/math.pk",
@@ -65,7 +66,7 @@ def main():
 def run_all_tests():
   ## get the interpreter.
   pocket = get_pocket_binary()
-  
+
   for suite in TEST_SUITE:
     print_title(suite)
     for test in TEST_SUITE[suite]:
@@ -142,7 +143,7 @@ def print_title(title):
   print("----------------------------------")
   print(" %s " % title)
   print("----------------------------------")
-  
+
 if __name__ == '__main__':
   ## This will enable ANSI codes in windows terminal.
   os.system('')

src/core/core.c

@@ -200,15 +200,21 @@ String* varToString(PKVM* vm, Var self, bool repr) {
     if (has_method) {
       Var ret = VAR_NULL;
       PkResult result = vmCallMethod(vm, self, closure, 0, NULL, &ret);
-      if (result != PK_RESULT_SUCCESS) return NULL;
 
-      if (!IS_OBJ_TYPE(ret, OBJ_STRING)) {
-        VM_SET_ERROR(vm, newString(vm, "method " LITS__str " returned "
-                                       "non-string type."));
-        return NULL;
+      if (!VM_HAS_ERROR(vm)) {
+        if (result != PK_RESULT_SUCCESS) return NULL;
+        if (!IS_OBJ_TYPE(ret, OBJ_STRING)) {
+          VM_SET_ERROR(vm, newString(vm, "method " LITS__str " returned "
+                                         "non-string type."));
+          return NULL;
+        }
+        return (String*)AS_OBJ(ret);
       }
 
-      return (String*)AS_OBJ(ret);
+      // already has error -> dealing with error message
+      if (result == PK_RESULT_SUCCESS && IS_OBJ_TYPE(ret, OBJ_STRING)) {
+        return (String*)AS_OBJ(ret);
+      }
     }
 
     // If we reached here, it doesn't have a to string override. just
@@ -437,6 +443,22 @@ DEF(coreAssert,
   }
 }
 
+DEF(coreRaise,
+  "raise([message:String]) -> Null",
+  "Raise a runtime error.") {
+
+  int argc = ARGC;
+  if (argc > 1) { // raise() or raise(message).
+    RET_ERR(newString(vm, "Invalid argument count."));
+  }
+
+  if (argc == 1 && ARG(1) != VAR_NULL) {
+    vm->fiber->error = ARG(1);
+    return;
+  }
+  VM_SET_ERROR(vm, newString(vm, "No exception to reraise."));
+}
+
 DEF(coreBin,
   "bin(value:Number) -> String",
   "Returns as a binary value string with '0b' prefix.") {
@@ -698,6 +720,7 @@ static void initializeBuiltinFunctions(PKVM* vm) {
   INITIALIZE_BUILTIN_FN("help",      coreHelp,    -1);
   INITIALIZE_BUILTIN_FN("dir",       coreDir,      1);
   INITIALIZE_BUILTIN_FN("assert",    coreAssert,  -1);
+  INITIALIZE_BUILTIN_FN("raise",     coreRaise,   -1);
   INITIALIZE_BUILTIN_FN("bin",       coreBin,      1);
   INITIALIZE_BUILTIN_FN("hex",       coreHex,      1);
   INITIALIZE_BUILTIN_FN("yield",     coreYield,   -1);
@@ -1377,6 +1400,26 @@ DEF(_fiberRun,
     self->caller = vm->fiber;
     vm->fiber = self;
     self->state = FIBER_RUNNING;
+    self->trying = false;
+  }
+}
+
+DEF(_fiberTry,
+  "Fiber.try(...) -> Var",
+  "The same as Fiber.run() but store the error message in 'error' attrib "
+  "instead of exiting.") {
+
+  ASSERT(IS_OBJ_TYPE(SELF, OBJ_FIBER), OOPS);
+  Fiber* self = (Fiber*) AS_OBJ(SELF);
+
+  // Switch fiber and start execution. New fibers are marked as running in
+  // either it's stats running with vmRunFiber() or here -- inserting a
+  // fiber over a running (callee) fiber.
+  if (vmPrepareFiber(vm, self, ARGC, &ARG(1))) {
+    self->caller = vm->fiber;
+    vm->fiber = self;
+    self->state = FIBER_RUNNING;
+    self->trying = true;
   }
 }
 
@@ -1484,6 +1527,7 @@ static void initializePrimitiveClasses(PKVM* vm) {
   ADD_METHOD(PK_MODULE, "globals", _moduleGlobals, 0);
 
   ADD_METHOD(PK_FIBER,  "run",    _fiberRun,      -1);
+  ADD_METHOD(PK_FIBER,  "try",    _fiberTry,      -1);
   ADD_METHOD(PK_FIBER,  "resume", _fiberResume,   -1);
 
 #undef ADD_METHOD
@@ -2087,6 +2131,9 @@ Var varGetAttrib(PKVM* vm, Var on, String* attrib) {
 
         case CHECK_HASH("function", 0x9ed64249):
           return VAR_OBJ(fb->closure);
+
+        case CHECK_HASH("error", 0x21918751):
+          return fb->error;
       }
     } break;
 

src/core/debug.c

@@ -214,15 +214,25 @@ static void _reportStackFrame(PKVM* vm, CallFrame* frame) {
   }
 }
 
-void reportRuntimeError(PKVM* vm, Fiber* fiber) {
+void reportRuntimeError(PKVM* vm, Fiber* fiber, bool* is_first) {
 
   pkWriteFn writefn = vm->config.stderr_write;
   if (writefn == NULL) return;
 
   // Error message.
-  _printRed(vm, "Error: ");
-  writefn(vm, fiber->error->data);
-  writefn(vm, "\n");
+  if (*is_first) {
+    _printRed(vm, "Error: ");
+    String* msg = NULL;
+    if (IS_OBJ_TYPE(fiber->error, OBJ_STRING)) {
+      msg = (String*)AS_OBJ(fiber->error);
+    } else {
+      msg = varToString(vm, fiber->error, false);
+    }
+
+    writefn(vm, msg->data);
+    writefn(vm, "\n");
+    *is_first = false;
+  }
 
   // If the stack frames are greater than 2 * max_dump_frames + 1,
   // we're only print the first [max_dump_frames] and last [max_dump_frames]

src/core/debug.h

@@ -18,7 +18,7 @@ void reportCompileTimeError(PKVM* vm, const char* path, int line,
                             const char* fmt, va_list args);
 
 // Pretty print runtime error.
-void reportRuntimeError(PKVM* vm, Fiber* fiber);
+void reportRuntimeError(PKVM* vm, Fiber* fiber, bool* first);
 
 // Dump opcodes of the given function to the stdout.
 void dumpFunctionCode(PKVM* vm, Function* func);

src/core/public.c

@@ -568,7 +568,11 @@ PkResult pkRunREPL(PKVM* vm) {
 
 void pkSetRuntimeError(PKVM* vm, const char* message) {
   CHECK_FIBER_EXISTS(vm);
-  VM_SET_ERROR(vm, newString(vm, message));
+  if (message != NULL) {
+    VM_SET_ERROR(vm, newString(vm, message));
+  } else {
+    VM_RESET_ERROR(vm);
+  }
 }
 
 void pkSetRuntimeErrorFmt(PKVM* vm, const char* fmt, ...) {
@@ -578,6 +582,18 @@ void pkSetRuntimeErrorFmt(PKVM* vm, const char* fmt, ...) {
   va_end(args);
 }
 
+void pkSetRuntimeErrorObj(PKVM* vm, int slot) {
+  CHECK_FIBER_EXISTS(vm);
+  VALIDATE_SLOT_INDEX(slot);
+  vm->fiber->error = ARG(slot);
+}
+
+void pkGetRuntimeError(PKVM* vm, int slot) {
+  CHECK_FIBER_EXISTS(vm);
+  VALIDATE_SLOT_INDEX(slot);
+  SET_SLOT(slot, vm->fiber->error);
+}
+
 void* pkGetSelf(const PKVM* vm) {
   CHECK_FIBER_EXISTS(vm);
   ASSERT(IS_OBJ_TYPE(vm->fiber->self, OBJ_INST), OOPS);
@@ -697,6 +713,7 @@ bool pkValidateSlotInstanceOf(PKVM* vm, int slot, int cls) {
   CHECK_FIBER_EXISTS(vm);
   VALIDATE_SLOT_INDEX(slot);
   VALIDATE_SLOT_INDEX(cls);
+  VM_RESET_ERROR(vm);
 
   Var instance = ARG(slot), class_ = SLOT(cls);
   if (!varIsType(vm, instance, class_)) {
@@ -710,9 +727,11 @@ bool pkValidateSlotInstanceOf(PKVM* vm, int slot, int cls) {
 }
 
 bool pkIsSlotInstanceOf(PKVM* vm, int inst, int cls, bool* val) {
+  CHECK_FIBER_EXISTS(vm);
   CHECK_ARG_NULL(val);
   VALIDATE_SLOT_INDEX(inst);
   VALIDATE_SLOT_INDEX(cls);
+  VM_RESET_ERROR(vm);
 
   *val = varIsType(vm, inst, cls);
   return !VM_HAS_ERROR(vm);
@@ -839,6 +858,7 @@ bool pkSetAttribute(PKVM* vm, int instance, const char* name, int value) {
   CHECK_ARG_NULL(name);
   VALIDATE_SLOT_INDEX(instance);
   VALIDATE_SLOT_INDEX(value);
+  VM_RESET_ERROR(vm);
 
   String* sname = newString(vm, name);
   vmPushTempRef(vm, &sname->_super); // sname.
@@ -854,6 +874,7 @@ bool pkGetAttribute(PKVM* vm, int instance, const char* name,
   CHECK_ARG_NULL(name);
   VALIDATE_SLOT_INDEX(instance);
   VALIDATE_SLOT_INDEX(index);
+  VM_RESET_ERROR(vm);
 
   String* sname = newString(vm, name);
   vmPushTempRef(vm, &sname->_super); // sname.
@@ -885,6 +906,7 @@ static Var _newInstance(PKVM* vm, Class* cls, int argc, Var* argv) {
 bool pkNewInstance(PKVM* vm, int cls, int index, int argc, int argv) {
   CHECK_FIBER_EXISTS(vm);
   VALIDATE_SLOT_INDEX(index);
+  VM_RESET_ERROR(vm);
 
   if (argc != 0) {
     VALIDATE_SLOT_INDEX(argv);
@@ -969,6 +991,7 @@ uint32_t pkListLength(PKVM* vm, int list) {
 
 bool pkCallFunction(PKVM* vm, int fn, int argc, int argv, int ret) {
   CHECK_FIBER_EXISTS(vm);
+  VM_RESET_ERROR(vm);
   ASSERT(IS_OBJ_TYPE(SLOT(fn), OBJ_CLOSURE), "Slot value wasn't a function");
   if (argc != 0) {
     VALIDATE_SLOT_INDEX(argv);
@@ -1009,6 +1032,7 @@ bool pkCallMethod(PKVM* vm, int instance, const char* method,
   CHECK_FIBER_EXISTS(vm);
   CHECK_ARG_NULL(method);
   VALIDATE_SLOT_INDEX(instance);
+  VM_RESET_ERROR(vm);
   if (argc != 0) {
     VALIDATE_SLOT_INDEX(argv);
     VALIDATE_SLOT_INDEX(argv + argc - 1);
@@ -1054,6 +1078,7 @@ void pkPlaceSelf(PKVM* vm, int index) {
 bool pkImportModule(PKVM* vm, const char* path, int index) {
   CHECK_FIBER_EXISTS(vm);
   VALIDATE_SLOT_INDEX(index);
+  VM_RESET_ERROR(vm);
 
   String* path_ = newString(vm, path);
   vmPushTempRef(vm, &path_->_super); // path_

src/core/value.c

@@ -233,8 +233,8 @@ static void popMarkedObjectsInternal(Object* obj, PKVM* vm) {
 
       markObject(vm, &fiber->caller->_super);
       markObject(vm, &fiber->native->_super);
-      markObject(vm, &fiber->error->_super);
 
+      markValue(vm, fiber->error);
       markValue(vm, fiber->self);
 
     } break;
@@ -495,6 +495,7 @@ Fiber* newFiber(PKVM* vm, Closure* closure) {
 
   fiber->open_upvalues = NULL;
   fiber->self = VAR_UNDEFINED;
+  fiber->error = VAR_NULL;
 
   // Initialize the return value to null (doesn't really have to do that here
   // but if we're trying to debut it may crash when dumping the return value).
@@ -1127,7 +1128,7 @@ Var mapRemoveKey(PKVM* vm, Map* self, Var key) {
 }
 
 bool fiberHasError(Fiber* fiber) {
-  return fiber->error != NULL;
+  return fiber->error != VAR_NULL;
 }
 
 void freeObject(PKVM* vm, Object* self) {

src/core/value.h

@@ -471,6 +471,8 @@ typedef enum {
 struct Fiber {
   Object _super;
 
+  bool trying;
+
   FiberState state;
 
   // The root closure of the fiber.
@@ -514,7 +516,7 @@ struct Fiber {
   Fiber *caller, *native;
 
   // Runtime error initially NULL, heap allocated.
-  String* error;
+  Var error;
 };
 
 struct Class {