Get expected behaviour; cleanup after confirming behaviour is desired

src/boot/boot.c

@@ -33,6 +33,12 @@
 extern const unsigned char *janet_gen_boot;
 extern int32_t janet_gen_boot_size;
 
+static Janet janet_set_repl_within_form(int32_t argc, Janet *argv) {
+    janet_fixarity(argc, 1);
+    (void) argv;
+    return janet_wrap_nil();
+}
+
 int main(int argc, const char **argv) {
 
     /* Init janet */
@@ -53,6 +59,8 @@ int main(int argc, const char **argv) {
 
     env = janet_core_env(NULL);
 
+    janet_def(env, "set-repl-within-form", janet_wrap_cfunction(janet_set_repl_within_form), "");
+
     /* Create args tuple */
     JanetArray *args = janet_array(argc);
     for (int i = 0; i < argc; i++)

src/boot/boot.janet

@@ -1978,7 +1978,7 @@
   (var going true)
 
   # The parser object
-  (def p (parser/new))
+  (var p (parser/new))
 
   # Evaluate 1 source form in a protected manner
   (defn eval1 [source]
@@ -2017,19 +2017,30 @@
   (while going
     (if (env :exit) (break))
     (buffer/clear buf)
-    (chunks buf p)
+    (if (nil? (chunks buf p))
+      (do
+        # Nil chunks represents a cancelled form in the REPL, so reset.
+        (set-repl-within-form false)
+        (set p (parser/new))
+        (buffer/clear buf))
+      (do
         (var pindex 0)
         (var pstatus nil)
         (def len (length buf))
         (when (= len 0)
           (parser/eof p)
           (set going false))
+        (if (= len 1)
+          (set-repl-within-form false)
+          (set-repl-within-form true))
         (while (> len pindex)
+          (set-repl-within-form true)
           (+= pindex (parser/consume p buf pindex))
           (while (parser/has-more p)
             (eval1 (parser/produce p)))
           (when (= (parser/status p) :error)
-        (parse-err p where))))
+            (parse-err p where))))))
+
   # Check final parser state
   (while (parser/has-more p)
     (eval1 (parser/produce p)))

src/mainclient/shell.c

@@ -25,6 +25,7 @@
 #endif
 
 #include <janet.h>
+#include <stdbool.h>
 
 #ifdef _WIN32
 #include <windows.h>
@@ -39,6 +40,10 @@ void janet_line_deinit();
 
 void janet_line_get(const char *p, JanetBuffer *buffer);
 Janet janet_line_getter(int32_t argc, Janet *argv);
+static Janet janet_set_repl_within_form(int32_t argc, Janet *argv);
+
+static JANET_THREAD_LOCAL bool gbl_cancel_current_repl_form = false;
+static JANET_THREAD_LOCAL bool gbl_repl_within_form = false;
 
 /*
  * Line Editing
@@ -54,7 +59,17 @@ Janet janet_line_getter(int32_t argc, Janet *argv) {
     gbl_complete_env = (argc >= 3) ? janet_gettable(argv, 2) : NULL;
     janet_line_get(str, buf);
     gbl_complete_env = NULL;
-    return janet_wrap_buffer(buf);
+
+    Janet result;
+    if (gbl_cancel_current_repl_form) {
+        gbl_cancel_current_repl_form = false;
+
+        // Signal that the user bailed out of the current form
+        result = janet_wrap_nil();
+    } else {
+        result = janet_wrap_buffer(buf);
+    }
+    return result;
 }
 
 static void simpleline(JanetBuffer *buffer) {
@@ -71,6 +86,12 @@ static void simpleline(JanetBuffer *buffer) {
     }
 }
 
+static Janet janet_set_repl_within_form(int32_t argc, Janet *argv) {
+    janet_fixarity(argc, 1);
+    gbl_repl_within_form = janet_unwrap_boolean(argv[0]) != 0;
+    return janet_wrap_nil();
+}
+
 /* Windows */
 #ifdef JANET_WINDOWS
 
@@ -746,8 +767,15 @@ static int line() {
                 kleft();
                 break;
             case 3:     /* ctrl-c */
+                if (
+                        (gbl_len == 0)
+                        && !gbl_repl_within_form
+                ) {   /* quit on empty line */
                     errno = EAGAIN;
                     gbl_sigint_flag = 1;
+                } else {              /* interrupt expression on non-empty line */
+                    gbl_cancel_current_repl_form = true;
+                }
                 clearlines();
                 return -1;
             case 4:     /* ctrl-d, eof */
@@ -947,6 +975,9 @@ void janet_line_get(const char *p, JanetBuffer *buffer) {
     }
     if (line()) {
         norawmode();
+        if (gbl_cancel_current_repl_form) {
+            fputc('\n', out);
+        } else {
             if (gbl_sigint_flag) {
                 raise(SIGINT);
             } else {
@@ -954,6 +985,7 @@ void janet_line_get(const char *p, JanetBuffer *buffer) {
             }
             return;
         }
+    }
     fflush(stdin);
     norawmode();
     fputc('\n', out);
@@ -991,6 +1023,7 @@ int main(int argc, char **argv) {
     /* Replace original getline with new line getter */
     JanetTable *replacements = janet_table(0);
     janet_table_put(replacements, janet_csymbolv("getline"), janet_wrap_cfunction(janet_line_getter));
+    janet_table_put(replacements, janet_csymbolv("set-repl-within-form"), janet_wrap_cfunction(janet_set_repl_within_form));
     janet_line_init();
 
     /* Get core env */