Aha!  So "subs" will force add to evaluate its operands - that's exactly what I needed!

So, I can leave my f, g and h the same, but then "set" the definition of g with

g:=subs(t=g(x), x->t)

and then evalhf(g(2)) returns a value.

This is a bit eccentric, but seems to work fine.  Does it meet your criteria for being effective?

Aha!  So "subs" will force add to evaluate its operands - that's exactly what I needed!

So, I can leave my f, g and h the same, but then "set" the definition of g with

g:=subs(t=g(x), x->t)

and then evalhf(g(2)) returns a value.

This is a bit eccentric, but seems to work fine.  Does it meet your criteria for being effective?