Distinguishing interactive and non-interactive functions or customizing `execute-extended-command'?

[Elena]

Hello,

I'd like to have some interactive command of mine whose name would
conflict with existing non-interactive functions.

For instance, I'd like to define an interactive "sort" command which
would act accordingly to context. However, a non-interactive `sort'
function already exists and I think that redefining it should be my
last (ugly) resort. I'd just like to find a way to type `M-x sort RET'
and having my own `sort' command executed.

Unless there is a way to distinguish between interactive and non-
interactive functions (I don't think so), I think I could customize
`execute-extended-command', but it's defined in C source code, and I'd
prefer to stay on the Emacs Lisp side.

Any hints? Thanks.