[Bug-apl] APL Questions

[Louis de Forcrand]

A few quick questions:

Is it possible to terminate a function while it's running
(eg. when you accidentally set a very large number 
as an operand)?

Take user input in as a vector of characters so the 
user doesn't have to add quotes? Something that
works like ⎕ but automatically wraps the input in quotes?
I read a bit of the APLX online manual just before posting, 
and I think ⍞ does this, right?

Edit a specific line in a function? As of now I'm writing my
long ∇-declared functions in in .txt files and loading them
with -f, otherwise I would have to rewrite (or copy-paste)
them back in line by line in the terminal.
From what I understand, the APLX manual also says that it
is possible to do this with ⍎'∇FN[3]←A+1', for example, which 
would change line 3 of function FN to A+1. I don't think this
works in GNU APL though.

What does the ⍫ (lock) symbol do to functions, and how do
I use it?

Thanks in advance,
Louis