Is it a closed definition? The equivalent in Mathematica would allow one to add things whenever one wants, for example to add definitions for fac for negative integers, or to hard-code the value of fac 100.
If clean has a REPL (which I couldn’t easily find out from its web page) I expect it to have that, too.
In Haskell it certainly is a closed definition, you would get a "multiple declarations" syntax error if you tried to split the definition up. I would assume the same for Clean also.
In the Haskell REPL, you would need to enter the definitions together.
If clean has a REPL (which I couldn’t easily find out from its web page) I expect it to have that, too.