OCaml: Match expression inside another one?

Question

I\'m currently working on a small project with OCaml; a simple mathematical expression simplifier. I\'m supposed to find certain patterns inside an expression, and simplify

Answer 1

You can make this terser (and I would argue clearer) by judicious use of underscores, as's and or-patterns. The resulting code is also more efficient, because it allocates less (in the Var, Sum and Prod cases)

let rec filter = function
| Var _ | Sum _ | Prod _ as e -> e
| Diff (_, (Sum _ | Diff _) as e) -> filter (diffRule e)
| Diff (_,e) -> e
| Quot (_, (Quot _| Prod _) as e) -> filter (quoteRule e)
| Quot (_,e) -> filter e
;;