prototyping functions in SML

Question

I have two functions, f and g, which call each other recursively. Unfortunately, when f calls g, it has not yet been declared, so I get an "unbound variable" error. How can I prototype (or whatever the equivalent vocabulary is) this function in SML/NJ?

Answer 1

Mutual Recursion. Use and instead of fun between the two functions.

Answer 2

Use and:

fun f x = ... 
and g x = ...

More info here.