Feature request: interactive shell #1

more details please !

I think it would be best to provide an example. Have you used python's interactive shell before? I will show a few examples and then tie that back to this issue.

Python interactive shell examples:

>>> x = 17
>>> x = x + 25
>>> print(x)
42
>>> for n in range(0, 10):
...     print(n)
...
0
1
2
3
4
5
6
7
8
9
>>> def my_print(str):
...     print(str)
...
>>> my_print('interactive shell')
interactive shell
>>>[Ctrl+C]
KeyboardInterrupt
>>>[Ctrl+D]
stangles-MBP:~ stangles$

The above snippet demonstrates a few things:

1. Variables in scope are preserved across commands. For the bf-interpreter, this would mean preserving "the tape" across input until the interactive shell session is ended.
2. Multi-line commands (such as function declarations and loops) are handled correctly
3. An interrupt halts the currently running command but keeps the interpreter running
4. An EOF input is required to exit the interpreter

These are the important pieces of functionality that I think the interactive shell feature should have. Let me know if you need any more details!