ghfwlc

Compared to Python, Common Lisp hardly has any performance issues.

Restarting from the debugger keeps state without third party Python hacks that you mention. In this example Python increments x twice, Lisp just once:

  >>> x = 0
  >>> def f():
  ...     global x # yuck!
  ...     x += 1
  ... 
  >>> def g(y):
  ...     h()
  ... 
  >>> 
  >>> g(f())
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "<stdin>", line 2, in g
  NameError: name 'h' is not defined
  >>> 
  >>> def h(): pass
  ... 
  >>> g(f())
  >>> 
  >>> x
  2

Versus:

  * (setf x 0)
  * (defun f() (incf x))
  * (defun g(y) (h))
  * (g(f))

  debugger invoked on a UNDEFINED-FUNCTION in thread
  #<THREAD "main thread" RUNNING {1001878103}>:
    The function COMMON-LISP-USER::H is undefined.

  Type HELP for debugger help, or (SB-EXT:EXIT) to exit from SBCL.

  restarts (invokable by number or by possibly-abbreviated name):
    0: [CONTINUE      ] Retry calling H.
    1: [USE-VALUE     ] Call specified function.
    2: [RETURN-VALUE  ] Return specified values.
    3: [RETURN-NOTHING] Return zero values.
    4: [ABORT         ] Exit debugger, returning to top level.

  ("undefined function")
  0] (defun h() nil)
  ; No debug variables for current frame: using EVAL instead of EVAL-IN-FRAME.
  H
  0] 0
  NIL
  * x
  1

Common Lisp is still the most pleasant REPL language. The only complaint I have is that too many function names are taken due to the large spec.