[m-rev.] for review: rationalise hash functions across the standard library

[Peter Wang]

On Tue, 11 Feb 2020 11:42:34 +1100 (AEDT), Julien Fischer <jfischer at opturion.com> wrote:
> 
> For review by Peter.
> 
> We discussed this on the developers list back in August 2019.
> 
> --------------------------------------------------------------------
> 
> Rationalise hash functions across the standard library.
> 
> Currently, the hash functions for (some of) the primitive types are defined in
> three places:
> 
>     1. The hash_table module.
>     2. The version_hash_table module (duplicates of the above).
>     3. Some (but not all) of the library modules for the primitive types.
> 
> This change makes the library module for a primitive type provide the hash
> function for that type and deprecates the versions in the hash table modules.
> 
> Additionally, deprecate the "generic" has functions in the hash table modules.
> 

Related: should we move towards using hash functions that return uints?
And, if we're breaking things, should the hash table modules take a
hash *function* instead of a predicate?


> diff --git a/library/char.m b/library/char.m
> index 04ecac3..59e2459 100644
> --- a/library/char.m
> +++ b/library/char.m
> @@ -397,6 +397,16 @@
>   :- pred det_int_to_digit(int::in, char::out) is det.
> 
>   %---------------------------------------------------------------------------%
> +%
> +% Computing hashes of charrs.
> +%

chars

> diff --git a/library/float.m b/library/float.m
> index 0d246d8..120ef09 100644
> --- a/library/float.m
> +++ b/library/float.m
...
> +uint_hash(Key, Hash) :-
> +    uint.hash(Key, Hash).
> 
> -float_hash(F, float.hash(F)).
> +float_hash(F, Hash) :-
> +    float.hash(F, Hash).
>       % There are almost certainly better ones out there...
> 
>   char_hash(C, H) :-
> +    char.hash(C, H).
>       % There are almost certainly better ones out there...
> -    int_hash(char.to_int(C), H).
> 
> -string_hash(S, string.hash(S)).
> +string_hash(S, H) :-
> +    string.hash(S, H).
>       % There are almost certainly better ones out there...
> 
>   %---------------------------------------------------------------------------%

Might as well delete the comments.

The rest looks fine.

Peter