janet_try macro and janet_restore function.

This allows catching panics without using pcall.

src/core/vm.c

@@ -1315,8 +1315,25 @@ static JanetSignal janet_check_can_resume(JanetFiber *fiber, Janet *out) {
     return JANET_SIGNAL_OK;
 }
 
+void janet_try_init(JanetTryState *state) {
+    state->stackn = janet_vm_stackn++;
+    state->gc_handle = janet_vm_gc_suspend;
+    state->vm_fiber = janet_vm_fiber;
+    state->vm_jmp_buf = janet_vm_jmp_buf;
+    state->vm_return_reg = janet_vm_return_reg;
+    janet_vm_return_reg = &(state->payload);
+    janet_vm_jmp_buf = &(state->buf);
+}
+
+void janet_restore(JanetTryState *state) {
+    janet_vm_stackn = state->stackn;
+    janet_vm_gc_suspend = state->gc_handle;
+    janet_vm_fiber = state->vm_fiber;
+    janet_vm_jmp_buf = state->vm_jmp_buf;
+    janet_vm_return_reg = state->vm_return_reg;
+}
+
 static JanetSignal janet_continue_no_check(JanetFiber *fiber, Janet in, Janet *out) {
-    jmp_buf buf;
 
     JanetFiberStatus old_status = janet_fiber_status(fiber);
 
@@ -1349,45 +1366,23 @@ static JanetSignal janet_continue_no_check(JanetFiber *fiber, Janet in, Janet *o
     }
 
     /* Save global state */
-    int32_t oldn = janet_vm_stackn++;
-    int handle = janet_vm_gc_suspend;
-    JanetFiber *old_vm_fiber = janet_vm_fiber;
-    jmp_buf *old_vm_jmp_buf = janet_vm_jmp_buf;
-    Janet *old_vm_return_reg = janet_vm_return_reg;
-
-    /* Setup fiber */
+    JanetTryState tstate;
+    JanetSignal signal = janet_try(&tstate);
+    if (!signal) {
+        /* Normal setup */
         if (janet_vm_root_fiber == NULL) janet_vm_root_fiber = fiber;
         janet_vm_fiber = fiber;
         janet_gcroot(janet_wrap_fiber(fiber));
         janet_fiber_set_status(fiber, JANET_STATUS_ALIVE);
-    janet_vm_return_reg = out;
-    janet_vm_jmp_buf = &buf;
-
-    /* Run loop */
-    JanetSignal signal;
-    int jmpsig;
-#if defined(JANET_BSD) || defined(JANET_APPLE)
-    jmpsig = _setjmp(buf);
-#else
-    jmpsig = setjmp(buf);
-#endif
-    if (jmpsig) {
-        signal = (JanetSignal) jmpsig;
-    } else {
         signal = run_vm(fiber, in);
     }
 
-    /* Tear down fiber */
+    /* Restore */
+    if (janet_vm_root_fiber == fiber) janet_vm_root_fiber = NULL;
     janet_fiber_set_status(fiber, signal);
     janet_gcunroot(janet_wrap_fiber(fiber));
-
-    /* Restore global state */
-    if (janet_vm_root_fiber == fiber) janet_vm_root_fiber = NULL;
-    janet_vm_gc_suspend = handle;
-    janet_vm_fiber = old_vm_fiber;
-    janet_vm_stackn = oldn;
-    janet_vm_return_reg = old_vm_return_reg;
-    janet_vm_jmp_buf = old_vm_jmp_buf;
+    janet_restore(&tstate);
+    *out = tstate.payload;
 
     return signal;
 }

src/include/janet.h

@@ -1030,6 +1030,19 @@ struct JanetFile {
     int32_t flags;
 };
 
+/* For janet_try and janet_restore */
+typedef struct {
+    /* old state */
+    int32_t stackn;
+    int gc_handle;
+    JanetFiber *vm_fiber;
+    jmp_buf *vm_jmp_buf;
+    Janet *vm_return_reg;
+    /* new state */
+    jmp_buf buf;
+    Janet payload;
+} JanetTryState;
+
 /* Thread types */
 #ifdef JANET_THREADS
 typedef struct JanetThread JanetThread;
@@ -1411,6 +1424,13 @@ JANET_API JanetBuffer *janet_pretty(JanetBuffer *buffer, int depth, int flags, J
 #define JANET_HASH_KEY_SIZE 16
 JANET_API void janet_init_hash_key(uint8_t key[JANET_HASH_KEY_SIZE]);
 #endif
+JANET_API void janet_try_init(JanetTryState *state);
+#if defined(JANET_BSD) || defined(JANET_APPLE)
+#define janet_try(state) (janet_try_init(state), (JanetSignal) _setjmp((state)->buf))
+#else
+#define janet_try(state) (janet_try_init(state), (JanetSignal) setjmp((state)->buf))
+#endif
+JANET_API void janet_restore(JanetTryState *state);
 JANET_API int janet_equals(Janet x, Janet y);
 JANET_API int32_t janet_hash(Janet x);
 JANET_API int janet_compare(Janet x, Janet y);

test/helper.janet

@@ -3,7 +3,6 @@
 (var num-tests-passed 0)
 (var num-tests-run 0)
 (var suite-num 0)
-(var numchecks 0)
 (var start-time 0)
 
 (defn assert
@@ -13,16 +12,8 @@
   (++ num-tests-run)
   (when x (++ num-tests-passed))
   (if x
-    (do
-      (when (= numchecks 25)
-        (set numchecks 0)
-        (print))
-      (++ numchecks)
-      (file/write stdout "\e[32m✔\e[0m"))
-    (do
-      (file/write stdout "\n\e[31m✘\e[0m  ")
-      (set numchecks 0)
-      (print e)))
+    (xprintf stdout "\e[32m✔\e[0m %s: %v" (string e) x)
+    (xprintf stdout "\n\e[31m✘\e[0m %s: %v" (string e) x))
   x)
 
 (defmacro assert-error