Function apply

pub fn apply<F>(tp: &mut TermPool, t: &ATerm, function: &F) -> ATerm
where
    F: Fn(&mut TermPool, &ATerm) -> Option<ATerm>,

Applies the given function to every subterm of the given term using the TermBuilder. function(subterm) returns: None , in which case subterm is kept and it is recursed into its argments. Some(x), in which case subterm is replaced by x.