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Functional LRU cache via association-list ordered most-recent-first. Get / put both: - find or remove the existing entry - cons the fresh (k, v) to the front - on put, trim the tail when over capacity Sequence: put 1 100; put 2 200; put 3 300 a = get 1 -> 100 (moves 1 to front) put 4 400 (evicts 2) b = get 2 -> -1 (no longer cached) c = get 3 -> 300 d = get 1 -> 100 a + b + c + d = 499 Tests `match … with (k', v) :: rest when k' = k -> …` tuple-cons patterns with `when` guards, `function` keyword for arg-less match, recursive find/remove/take over the same list. Parser limit found: `match n, lst with` ad-hoc tuple-scrutinee is not yet supported (got "expected op -> got op ,"); workaround uses outer `if` plus inner match. 171 baseline programs total.
52 lines
988 B
OCaml
52 lines
988 B
OCaml
let cache = ref []
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let cap = 3
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let get k =
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let rec find = function
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| [] -> None
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| (k', v) :: _ when k' = k -> Some v
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| _ :: rest -> find rest
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in
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match find !cache with
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| None -> -1
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| Some v ->
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let rec remove = function
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| [] -> []
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| (k', _) :: rest when k' = k -> rest
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| h :: rest -> h :: remove rest
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in
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cache := (k, v) :: remove !cache;
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v
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let put k v =
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let rec remove = function
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| [] -> []
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| (k', _) :: rest when k' = k -> rest
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| h :: rest -> h :: remove rest
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in
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let cleaned = remove !cache in
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let trimmed =
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if List.length cleaned >= cap then
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let rec take n lst =
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if n = 0 then []
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else match lst with
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| [] -> []
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| h :: r -> h :: take (n - 1) r
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in
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take (cap - 1) cleaned
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else cleaned
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in
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cache := (k, v) :: trimmed
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;;
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put 1 100;
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put 2 200;
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put 3 300;
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let a = get 1 in
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put 4 400;
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let b = get 2 in
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let c = get 3 in
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let d = get 1 in
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a + b + c + d
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