`type 'a equal = 'a -> 'a -> bool`

### Value interface

Typical use case: one wants to memoize a function `f : 'a -> 'b`

. Code sample:

```
let f x =
print_endline "call f";
x + 1;;
let f' = with_cache (lru 256) f;;
f' 0;; (* prints *)
f' 1;; (* prints *)
f' 0;; (* doesn't print, returns cached value *)
```

`val clear : (_, _) t -> unit`

Clear the content of the cache.

`type ('a, 'b) callback = in_cache:bool -> 'a -> 'b -> unit`

Type of the callback that is called once a cached value is found or not. Should never raise.

`val with_cache : ?cb:('a, 'b) callback -> ('a, 'b) t -> ('a -> 'b) -> 'a -> 'b`

`with_cache c f`

behaves like `f`

, but caches calls to `f`

in the cache `c`

. It always returns the same value as `f x`

, if `f x`

returns, or raise the same exception. However, `f`

may not be called if `x`

is in the cache.

```
val with_cache_rec :
?cb:('a, 'b) callback ->
('a, 'b) t ->
(('a -> 'b) -> 'a -> 'b) ->
'a ->
'b
```

`with_cache_rec c f`

is a function that first, applies `f`

to some `f' = fix f`

, such that recursive calls to `f'`

are cached in `c`

. It is similar to `with_cache`

but with a function that takes as first argument its own recursive version. Example (memoized Fibonacci function):

```
let fib = with_cache_rec (lru 256)
(fun fib' n -> match n with
| 1 | 2 -> 1
| _ -> fib' (n-1) + fib' (n-2)
);;
fib 70;;
```

`val size : (_, _) t -> int`

Size of the cache (number of entries). At most linear in the number of entries.

`val iter : ('a, 'b) t -> ('a -> 'b -> unit) -> unit`

Iterate on cached values. Should yield `size cache`

pairs.

`val add : ('a, 'b) t -> 'a -> 'b -> bool`

Manually add a cached value. Return `true`

if the value has successfully been added, and `false`

if the value was already bound.

Dummy cache, never stores any value.

`val linear : eq:'a equal -> int -> ('a, 'b) t`

Linear cache with the given size. It stores key/value pairs in an array and does linear search at every call, so it should only be used with small size.

`val replacing : eq:'a equal -> ?hash:'a hash -> int -> ('a, 'b) t`

Replacing cache of the given size. Equality and hash functions can be parametrized. It's a hash table that handles collisions by replacing the old value with the new (so a cache entry is evicted when another entry with the same hash (modulo size) is added). Never grows wider than the given size.

`val lru : eq:'a equal -> ?hash:'a hash -> int -> ('a, 'b) t`

LRU cache of the given size ("Least Recently Used": keys that have not been used recently are deleted first). Never grows wider than the given size.

`val unbounded : eq:'a equal -> ?hash:'a hash -> int -> ('a, 'b) t`

Unbounded cache, backed by a Hash table. Will grow forever unless `clear`

is called manually.