module type HashedType = sig .. end
The input signature of the functor Hashtbl.Make.
type t
The type of the hashtable keys.
val equal : t -> t -> bool
The equality predicate used to compare keys.
val hash : t -> int
A hashing function on keys. It must be such that if two keys are equal according to equal, then they have identical hash values as computed by hash. Examples: suitable (equal, hash) pairs for arbitrary key types include
(=), Hashtbl.hash) for comparing objects by structure (provided objects do not contain floats)(fun x y -> compare x y = 0), Hashtbl.hash) for comparing objects by structure and handling nan correctly(==), Hashtbl.hash) for comparing objects by physical equality (e.g. for mutable or cyclic objects).
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https://www.ocaml.org/releases/4.11/htmlman/libref/Hashtbl.HashedType.html