Matching on structured primitives

[rtzam]

(rewrite
    (Const (rational a b))
    (Mul (Const (rational -1 1)) (Const (rational (* -1 a) b)))
    :when ((< a 0))
    :ruleset builtin-rules)

Hi! It would be super cool to match on the integers inside a rational number as in the above code snippet.

[saulshanabrook]

I told Ryan he could use the functions instead, but this seems like a common things people might want and also connects to matching more generally on container sorts.