oh I had a similar problem when decoding powerpc instructions. What I ended up
with was a macro which among other things "unrolled" the branches using a
table. This would look kind off like this for your example:
const offsets: array[Sym, int] = [ord(high(Sym))+1, 0, 0, #[ecetera]#]
case ord(a.kind) + offsets[a.kind]
# all the cases which can be decoded based on the first part
of 0: discard
of 1: discard
# …
of ord(high(Sym))+1: # when a.kind == symNumber and b.kind == symNumber:
discard
of ord(high(Sym))+2: # when a.kind == symNumber and b.kind == symSymbol:
discard
Run
Another advantage this brought me was that I could use computed goto for the
interpreter.
