map_basics.mere

// Phase 12.10: Map[R, K, V] — region-aware mutable associative map.
//
// Design context: internal design notes §5
//
// `Map[R, K, V]` is a region-scoped mutable associative array. It follows
// the same construction-time binding pattern as Vec[R, T] / StrBuf[R].
// Internally it uses OCaml Hashtbl (polymorphic hash/eq), with the
// expectation that Lang's primitive values (int / str / bool / tuple of
// primitives) are used as keys.
//
// API:
//   map_new : unit -> Map[R, K, V]       (binds to region, or __heap if outside)
//   map_set : Map[R, K, V] -> K -> V -> unit
//   map_get : Map[R, K, V] -> K -> V     (eval error if key is absent)
//   map_has : Map[R, K, V] -> K -> bool
//   map_len : Map[R, K, V] -> int
//   len (polymorphic) : Map[R, K, V] -> int also works the same way

{
  // === Pattern 1: simple str -> int map ===
  let counts = map_new () in
  let _ = map_set counts "apple" 3 in
  let _ = map_set counts "banana" 5 in
  let _ = map_set counts "cherry" 2 in
  let _ = print ("apple count = " ++ show (map_get counts "apple")) in
  let _ = print ("total = " ++ show (
    map_get counts "apple" + map_get counts "banana" + map_get counts "cherry")
  ) in
  let _ = print ("map_len = " ++ show (map_len counts)) in

  // === Pattern 2: safely get after checking existence with map_has ===
  let lookup =
    if map_has counts "apple" then map_get counts "apple"
    else 0 in
  let missing_ok =
    if map_has counts "absent" then map_get counts "absent"
    else (-1) in
  let _ = print ("present  = " ++ show lookup) in
  let _ = print ("missing  = " ++ show missing_ok) in

  // === Pattern 3: int -> str (works naturally with reversed types) ===
  let codes = map_new () in
  let _ = map_set codes 1 "ok" in
  let _ = map_set codes 404 "not found" in
  let _ = map_set codes 500 "server error" in
  let _ = print ("status 404 = " ++ map_get codes 404) in

  // === Pattern 4: build a short-lived map inside a region ===
  let summary =
    region R {
      let acc = map_new () in           // type: Map[R, str, int]
      let _ = map_set acc "a" 1 in
      let _ = map_set acc "b" 2 in
      let _ = map_set acc "c" 3 in
      // the map is bulk-freed at the end of the region (Trivial); only the
      // result is converted to str and carried out
      "items=" ++ show (len acc)
    }
  in
  print summary
}

// Expected output:
// apple count = 3
// total = 10
// map_len = 3
// present  = 3
// missing  = -1
// status 404 = not found
// items=3