Defining a conditional statement for a function

Question

I am trying to define a function that is zero when it is evaluated on real numbers and on a preset list of symbols. I am doing this by using

f[x_]:=0/;Element[x,Reals]||MemberQ[{m,a,b},x]

where {m,a,b} are the set of symbols I want the function to be zero on. The problem is, I can't seem to set more rules for the function f. For example, if I try to set the rule

newRule= {f[x_]:>g[x]+q[x]}

Mathematica evaluates this to

newRule={0:>g[x]+q[x]}

How should a set the pattern for f so that I can make rules that do not evaluate to zero?

I am using Mathematica 11.

Answer 1

You may use multiple definitions for $f$, perhaps something like this:

ClearAll[f]
f[x_?NumericQ] := 0
f[x_?(MemberQ[{m, a, b}, #] &)] := 0
f[x_] := g[x] + q[x]

See sample outputs:

f[3]     (* 0 *)
f[Pi]    (* 0 *)
f[1.2]   (* 0 *)

f[a]     (* 0 *)
f[c]     (* g[c] + q[c] *)