An OCaml library for memoïzation
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 `{0 Usage}` ``` ``` `If you had a function [fibo] defined like this:` ``` ``` `{[` `let rec fibo x =` ` if x < 0 then invalid_arg "fibo";` ` if x < 2 then x` ` else fibo (x - 1) + fibo (x - 2)` `]}` ``` ``` `There's many different ways to memoïze it.` ``` ``` `{1:simple_memo Simple memoïzation}` ``` ``` `The easiest one is to rewrite it like this:` ``` ``` `{[` `let fibo = Memo.memo (fun fibo x ->` ` if x < 0 then invalid_arg "fibo";` ` if x < 2 then x` ` else fibo (x - 1) + fibo (x - 2))` `]}` ``` ``` `It'll use the {!module:Hashtbl} module from {!module:Stdlib} directly.` ``` ``` `I'd like to thank {{:https://www.lri.fr/~conchon/}Sylvain Conchon} who taught me memoïzation and how to write this [memo] function when I was his student.` ``` ``` `{1:custom_memo Using your own type, [equal] and [hash] functions}` ``` ``` `We provide a {!module:Memo.Make} functor. It can be useful in case you don't want to use polymorphic equality or you are doing things like {{:https://en.wikipedia.org/wiki/Hash_consing}hash consing} and you know how to compare or hash your type more efficiently.` ``` ``` `{[` `let module Mem = Memo.Make(struct` ` type t = int` ` let equal = (=)` ` let hash = Hashtbl.hash` `end)` ``` ``` `let fibo = Mem.memo (fun fibo x ->` ` if x < 0 then invalid_arg "fibo";` ` if x < 2 then x` ` else fibo (x - 1) + fibo (x - 2))` `]}` ``` ``` `{1:forgetful_memo Forgetful memoïzation}` ``` ``` `We provide a {!module:Memo.MakeWeak} functor. It works like the previous one, but the bindings in the memoïzation cache will be weak, allowing the garbage collector to remove them if they are not used somewhere else.` ``` ``` `{[` `let module Mem = Memo.MakeWeak(struct` ` type t = int` ` let equal = (=)` ` let hash = Hashtbl.hash` `end)` ``` ``` `let fibo = Mem.memo (fun fibo x ->` ` if x < 0 then invalid_arg "fibo";` ` if x < 2 then x` ` else fibo (x - 1) + fibo (x - 2))` `]}` ``` ``` `I'd like to thank {{:https://www.lri.fr/~filliatr/}Jean-Christophe Filliâtre} who taugh me forgetful memoïzation when I was doing research on {{:https://en.wikipedia.org/wiki/Binary_decision_diagram}binary decision diagram} under his direction while I was a first year master student.` ``` ``` `{1:fake_memo Fake memoïzation}` ``` ``` `We provide a {!module:Memo.Fake} functor. It is useful if you want to quickly test a function you memoïzed with our {!module:Memo.Make} or {!module:Memo.MakeWeak} functor, but without memoïzing it. It'll basically do nothing and should be equivalent to your initial non-memoïzed function.` ``` ``` `{[` `let module Mem = Memo.Fake(struct` ` type t = int` ` let equal = (=)` ` let hash = Hashtbl.hash` `end)` ``` ``` `let fibo = Mem.memo (fun fibo x ->` ` if x < 0 then invalid_arg "fibo";` ` if x < 2 then x` ` else fibo (x - 1) + fibo (x - 2))` `]}` ``` ``` `{1:custom_cache Using your own defined cache}` ``` ``` `With the {!module:Memo.Mk} functor, you can also directly provide a [Cache] module, which should have the signature {!module-type:Hashtbl.S}. We will include your cache module and use it to define a [memo] function:` ``` ``` `{[` `let module Mem = Memo.Mk(` ` Hashtbl.Make(struct` ` type t = int` ` let equal = (=)` ` let hash = Hashtbl.hash` ` end)` `end)` ``` ``` `let fibo = Mem.memo (fun fibo x ->` ` if x < 0 then invalid_arg "fibo";` ` if x < 2 then x` ` else fibo (x - 1) + fibo (x - 2))` `]}` ``` ``` `This example is useless and equivalent to using the {!module:Memo.Make} functor directly.` ``` ``` `If you find a real use case for this which doesn't need new dependencies, contact me and I'll be happy to add a new functor to the library.` ``` ``` `It should be useful only if you want to use another {!module:Hashtbl} implementation or things like this.` ``` ``` `{1:tuning Tuning}` ``` ``` `There's a default value for the initial cache size. You can set it to the value of your choice, reset it to the default and get the current value like this:` ``` ``` `{[` `Memo.set_initial_cache_size 1024;` `Memo.reset_initial_cache_size ();` `let curr_size = Memo.get_initial_cache_size ()` `]}` ``` ``` ```Note that with the current implementation of hash tables in OCaml, it's better if you choose a power of two. You may saw some code using a prime number, it's because some years ago it was the best thing to do as the hash tables implementation was different. {{:https://www.lri.fr/~filliatr/}Jean-Christophe Filliâtre} explained this to me, thanks again ! Also keep in mind that if you use your own defined cache thanks to the {!module:Memo.Mk} functor, it may not be the right thing to do. ```