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Pack hashtbl -- prolog/hashtbl/utils.pl
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Both variants of the hashtbl library share a common data representation: A hash table is a term nb_hashtbl/2 or p_hashtbl/2. The first argument contains metadata such as the hash table's current load. The second is a term bucket/N containing the hash buckets. Hash buckets are lists of Key-Values pairs where Key is a hash table key (a ground term) and Values is the list of Values associated with that key. Each key only occurs once in the table. When several values are added for the same key, later ones come before the older ones in the Values list. They have "higher priority" and are said to "shadow" the older values.

Due to this common representation of hash tables, many operations are identical on the two variants, differing only in the outermost functor. These non-destructive common operations, such as getting values from the table, or mapping higher-order predicates over the table, are defined in this module.

The concrete implementations of the hash tables use the predicates from this module. This is the only intended use of this module: It should be treated as internal to the library. Clients of the library should use one of the concrete hash table modules.

- Gergö Barany <gergo@tud.at>
 hashtbl_default_size(-N) is det
N is the default number of buckets in a newly created hash table.
 hashtbl_bucket(+Table, +Key, -BucketTerm, -BucketIdx, -Bucket) is det
Finds the hash bucket in Table for the given Key. BucketTerm is the Table's term holding the hash buckets, BucketIdx is the argument index into the BucketTerm (as for arg/3) of the hash bucket corresponding to the Key, and Bucket is the corresponding hash bucket. Always succeeds, even if Key is not in the Table.
 hashtbl_load(+Table, -Load) is det
Load is the current number of keys stored in Table.
 hashtbl_buckets(+Table, -Buckets) is det
Buckets is the number of hash buckets in Table.
 hashtbl_get(+Table, +Key, -Value) is semidet
Gets the most recently stored Value for Key in Table, if any. Fails if no values are stored for Key. There is no separate predicate for membership checks, use nb_hashtbl_get(Table, Key, _) to test whether Key is present in Table.
 hashtbl_get_all(+Table, +Key, -Value) is nondet
On backtracking, enumerates every Value associated with Key in Table. Fails if no values are stored for Key. The order of enumeration is the most recently added value for Key first (the same as the solution for nb_hashtbl_get/3), then shadowed ones.
 hashtbl_enumerate(+Table, -Key, -Value) is nondet
On backtracking, enumerates every Key-Value pair stored in the Table. Fails if the table is empty. If several values are stored for the same key, their order of enumeration is most recent first, as in hashtbl_get_all/3. The ordering is otherwise unspecified.

If Key is ground, this behaves like hashtbl_get_all/3 for that Key. However, hashtbl_get_all/3 is more efficient in this case.

 hashtbl_to_list(+Table, -Pairs) is det
Unifies Pairs with a list of all Key-Value pairs in the order as enumerated by nb_hashtbl_enumerate/3.
 key_value_cons(?Key, ?Value, ?Acc, ?List) is det
List is a list with head Key-Value and tail Acc.
 hashtbl_map(+Table, :Goal, -TableOut) is nondet
For every Key and Value in Table, calls Goal(Key, Value, Value1) and unifies TableOut with a hash table containing all Key-Value1 pairs. Deterministic if Goal is deterministic. If Goal backtracks, hashtbl_map/3 enumerates several TableOut tables accordingly.
 hashtbl_fold(+Table, :Goal, +Acc, -Result) is nondet
Folds Goal over every Key and Value in the Table. Calls Goal(Key, Value, Acc, Result), using each call's Result as the next call's accumulator Acc, and unifying Result with the final call's Result. Deterministic if Goal is deterministic. If Goal backtracks, enumerates several results accordingly.
 hashtbl_iter(+Table, :Goal) is nondet
Calls Goal(Key, Value) for every Key and Value stored in Table. This is useful to ensure that all entries satisfy some predicate, or for Goal's side effects. Deterministic if Goal is deterministic.