Pattern Matching

Pattern Matching

Pattern matching is one of OCaml's most powerful features. Use match ... with:

let describe n =
  match n with
  | 0 -> "zero"
  | 1 -> "one"
  | _ -> "other"

Matching Lists

let rec length lst =
  match lst with
  | [] -> 0
  | _ :: rest -> 1 + length rest

The Wildcard _

The underscore matches anything and serves as a catch-all:

let is_zero n =
  match n with
  | 0 -> true
  | _ -> false

Your Task

Write a function describe_list that returns "empty" for an empty list, "singleton" for a one-element list, and "long" for anything else.