Exit IPython with backspace

Author: tkf

README.md

@@ -11,10 +11,12 @@
 ## Usage
 
 Run `using IPython` and then type `.` in empty `julia>` prompt or run
-`IPython.start_ipython()`.  Exiting IPython as usual (e.g., `Ctrl-D`)
-brings you back to the Julia REPL.  Re-entering IPython keeps the
-previous state.  Use pre-defined `Main` object to access Julia
-namespace from IPython.
+`IPython.start_ipython()`.  If you are using IPython 7.0 or above, you
+can switch back to Julia REPl by `backspace` or `ctrl-h` key (like
+other REPL modes).  For older versions of IPython, exiting IPython as
+usual (e.g., `ctrl-d`) brings you back to the Julia REPL.  Re-entering
+IPython keeps the previous state.  Use pre-defined `Main` object to
+access Julia namespace from IPython.
 
 **Note:**
 First launch of IPython may be slow.

src/replhelper/ipyext.py

@@ -1,5 +1,15 @@
 from .core import get_cached_api
 
+try:
+    from .key_bindings import register_key_bindings
+except ImportError:
+    def register_key_bindings(_):
+        return lambda: None
+
+
+def _unregister_key_bindings():
+    """ No-op placeholder function to be replaced. """
+
 
 def julia_completer(julia, self, event):
     pos = event.line.find("Main.eval")
@@ -26,9 +36,16 @@ def _julia_completer(self, event):
 
 
 def load_ipython_extension(ip):
+    global _unregister_key_bindings
+    _unregister_key_bindings = register_key_bindings(ip)
+
     ip.set_hook("complete_command", _julia_completer,
                 re_key=r""".*\bMain\.eval\(["']""")
 # See:
 # https://ipython.readthedocs.io/en/stable/api/generated/IPython.core.hooks.html
 # IPython.core.interactiveshell.init_completer
 # IPython.core.completerlib (quick_completer etc.)
+
+
+def unload_ipython_extension(ip):
+    _unregister_key_bindings()

src/replhelper/key_bindings.py

@@ -0,0 +1,24 @@
+from prompt_toolkit.application.current import get_app
+from prompt_toolkit.filters import Condition
+
+
+@Condition
+def is_buffer_empty():
+    return get_app().current_buffer.text.strip() == ""
+
+
+def register_key_bindings(ip):
+    try:
+        add = ip.pt_app.key_bindings.add
+    except AttributeError:
+        return lambda: None
+
+    @add("c-h", filter=is_buffer_empty, eager=True)
+    def exit_with_backspace(event):
+        ip.ask_exit()
+        event.app.exit()
+
+    def unregister():
+        ip.pt_app.key_bindings.remove(exit_with_backspace)
+
+    return unregister