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hashing library that is generic on the hashing function, and a ppx deriving plugin for type-directer hashers

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imandra-ai/mhash

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Mhash + ppx_deriving_mhash build

This project contains:

  • mhash, to implement hashing for types in a way that is compatible with many concrete hashing functions
  • ppx_deriving_mhash to automatically derive such hashers

The mhash library comes with an implementation of the FNV algorithm.

Using the ppx

After adding (preprocess (pps ppx_deriving_hhash)) in dune, this should work:

# type foo = {
  x : int;
  y : string;
} [@@deriving mhash] ;;
type foo = { x : int; y : string; }
val hasher_foo : foo Mhash.hasher =
  {Mhash.hash_into = <fun>}
val hash_foo : algo:('a, 'b) Mhash.hash_algo -> foo -> 'b =
  <fun>

# #require "mhash.fnv";;
# hash_foo ~algo:Mhash_fnv.int {x=1; y="foo"};;
- : int = 3535931368763302282

Attributes

  • [@nohash] on a type will skip hashing for this type. Useful when a type declaration contains some function fields, or other fields that shouldn't affect the hash.
  • [@hasher <expr>] forces the ppx to use <expr> as the hasher for the given type. The attribute for a type ty must be an expression of type ty Mhash.hasher

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hashing library that is generic on the hashing function, and a ppx deriving plugin for type-directer hashers

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