This module defines impure (imperative) hash tables that allow destructive updates.

The predicates in this module use destructive non-backtrackable updates to implement the hash table. The basic operation used internally to implement changes to the hash table is nb_linkarg/3. Use with care.

The user should take care never to copy a non-backtrackable hash table. This includes never using asserta/1 or assertz/1 to store it in the database. If the table is to be stored in a global variable, nb_linkval/2 should be used for the purpose.

author

- Gergö Barany <gergo@tud.at>

license

- LGPL

 empty_nb_hashtbl(-Table) is det

Unifies Table with a newly created empty hash table of a default size.

 empty_nb_hashtbl(-Table, +Size) is det

Unifies Table with a newly created empty hash table with the number of buckets given by Size.

throws

- Type or domain error if Size is not a non-negative integer.

 nb_hashtbl_put(!Table, +Key, +Value) is det

Puts the Value into the Table at Key. If there are already values stored for Key, this new value will shadow them until it is deleted from the table.

 nb_hashtbl_set(!Table, +Key, +Value) is det

Sets the Value associated with Key in Table. If there are already values stored for Key in Table, the most recent one will is overwritten. If that entry shadowed earlier entries for Key, those remain shadowed and unchanged.

 nb_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.

 nb_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.

 nb_hashtbl_get_default(!Table, +Key, ?Default, -Value) is det

If Table contains an entry for Key, unifies Value with the corresponding value as in nb_hashtbl_get/3. Otherwise, unifies Value with Default and adds this value to the Table under Key.

 nb_hashtbl_delete(!Table, +Key) is det

Deletes the most recent value stored under Key in Table, if any. Does nothing otherwise; succeeds always.

 nb_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 nb_hashtbl_get_all/3. The ordering is otherwise unspecified.

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

 nb_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.

 list_to_nb_hashtbl(+Pairs, -Table) is semidet

If Pairs is a list of Key-Value pairs, unifies Table with a corresponding hash table of a default size containing all those pairs. If there are several entries for the same Key in the list, later entries will shadow earlier ones in the Table.

 list_to_nb_hashtbl(+Pairs, -Table, +Size) is semidet

As list_to_nb_hashtbl/2, but the hash table has an initial number of buckets given by Size.

throws

- Type or domain error if Size is not a non-negative integer.

 nb_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, nb_hashtbl_map/3 enumerates several TableOut tables accordingly.

 nb_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.

 nb_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.

 nb_hashtbl_unfold(:Goal, -Table) is det

Unfolds the binary goal Goal into the Table: Unifies Table with a hash table containing a Key-Value entry for every solution of Goal(Key, Value). Table is empty if Goal has no solutions. Later solutions of Goal will shadow earlier ones in Table.