[Haskell-cafe] How to express a logic matrix clearly?

[Magicloud Magiclouds]

Hi,
I have trouble describing this clearly. Let me show code directly.

data Rule1 = A1 | A2 | A3
data Rule2 = B1 | B2 | B3

foo a b =
  if a == A1
    then if b == B1
      then fun1
      else if b == B2
        then fun2
        else if b == B3
          then fun3
          else fun4
...

Basically, Rule1 and Rule2 compose a matrix, for each case of Rule1
and Rule2, I need to do different things. Above is already long and
not quite clear, and it is far from complete.

So my question is, is there a way/lib that I can make this clear to
read/understand?