How can I tell programmatically if a function has evaluated in a nontrivial way?
I'd like to do, essentially, something along the lines of f[x]===HoldForm[f[x]]
, a test that returns true if f[x]
just evaluates to f[x]
because it's not defined, or else false if f[x]
actually does something. Of course, that example code doesn't work - my guess is that the HoldForm is printing itself or something.