Doesn't seem to work with pypy3 either...

[dionyziz]

Your example doesn't work with CPython, but it doesn't seem to work with pypy3 either:

dionyziz@puppy ~ % pypy3 4.py
Traceback (most recent call last):
  File "4.py", line 29, in <module>
    print(make_change(27, [1, 5, 10, 25]))
  File "/usr/local/Cellar/pypy3/7.3.1_1/libexec/site-packages/guac/monad.py", line 102, in monadic_context
    return monad._run(f(*args, **kwargs))
  File "/usr/local/Cellar/pypy3/7.3.1_1/libexec/site-packages/guac/monad.py", line 49, in _run
    return step(next(computation), computation)
  File "/usr/local/Cellar/pypy3/7.3.1_1/libexec/site-packages/guac/monad.py", line 47, in step
    return self.bind(monadic_value, proceed)
  File "/usr/local/Cellar/pypy3/7.3.1_1/libexec/site-packages/guac/instances.py", line 32, in bind
    result += f(elem)
  File "/usr/local/Cellar/pypy3/7.3.1_1/libexec/site-packages/guac/monad.py", line 40, in proceed
    invocation = copy.deepcopy(continuation) # Requires Pypy!
  File "/usr/local/Cellar/pypy3/7.3.1_1/libexec/lib-python/3/copy.py", line 180, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/local/Cellar/pypy3/7.3.1_1/libexec/lib-python/3/copy.py", line 274, in _reconstruct
    y = func(*args)
  File "/usr/local/Cellar/pypy3/7.3.1_1/libexec/lib-python/3/copyreg.py", line 88, in __newobj__
    return cls.__new__(cls, *args)
TypeError: object.__new__(generator) is not safe, use generator.__new__()

I'm using this version:

Python 3.6.9 (?, Apr 18 2020, 02:46:07)
[PyPy 7.3.1 with GCC 4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.32.59)]