diff --git a/library/bhash.yap b/library/bhash.yap
new file mode 100644
index 000000000..f3985b23b
--- /dev/null
+++ b/library/bhash.yap
@@ -0,0 +1,165 @@
+/* 
+
+This code implements hash-arrays.
+It requires the hash key to be a ground term.
+
+It relies on dynamic array code.
+
+*/
+:- source.
+:- yap_flag(unknown,error).
+:- style_check(all).
+
+:- module(b_hash, [    b_hash_new/1,
+		      b_hash_new/2,
+		      b_hash_new/3,
+		      b_hash_lookup/3,
+		      b_hash_update/3,
+		      b_hash_update/4,
+		      b_hash_insert/3
+		    ]).
+
+:- use_module(library(terms), [ term_hash/4 ]).
+
+array_default_size(4).
+
+b_hash_new(hash(Keys, Vals, Size, N, _)) :-
+	array_default_size(Size),
+	array(Keys, Size),
+	array(Vals, Size),
+	create_mutable(0, N).
+
+b_hash_new(hash(Keys,Vals, Size, N, _), Size) :-
+	array(Keys, Size),
+	array(Vals, Size),
+	create_mutable(0, N).
+
+b_hash_new(hash(Keys,Vals, Size, N, HashF), Size, HashF) :-
+	array(Keys, Size),
+	array(Vals, Size),
+	create_mutable(0, N).
+
+b_hash_lookup(Key, Val, hash(Keys, Vals, Size, F)):-
+	hash_f(Key, Size, Index, F),
+	term_hash(Key,-1,Size,Index),
+	fetch_key(Keys, Index, Size, Key, ActualIndex),
+	array_element(Vals, ActualIndex, Mutable),
+	get_mutable(Val, Mutable).
+
+fetch_key(Keys, Index, Size, Key, ActualIndex) :-
+	array_element(Keys, Index, El),
+	nonvar(El),
+	(
+	    El == Key
+	->
+	    Index = ActualIndex
+	;
+	    I1 is (Index+1) mod Size,
+	    fetch_key(Keys, I1, Size, Key, ActualIndex)
+	).
+
+b_hash_update(Hash, Key, NewVal):-
+	Hash = hash(Keys, Vals, Size, _, F),
+	hash_f(Key,Size,Index,F),
+	fetch_key(Keys, Index, Size, Key, ActualIndex),
+	array_element(Vals, ActualIndex, Mutable),
+	update_mutable(NewVal, Mutable).
+
+b_hash_update(Hash, Key, OldVal, NewVal):-
+	Hash = hash(Keys, Vals, Size, _, F),
+	hash_f(Key,Size,Index,F),
+	fetch_key(Keys, Index, Size, Key, ActualIndex),
+	array_element(Vals, ActualIndex, Mutable),
+	get_mutable(OldVal, Mutable),
+	update_mutable(NewVal, Mutable).
+
+b_hash_insert(Hash, Key, NewVal):-
+	Hash = hash(Keys, Vals, Size, N, F),
+	hash_f(Key,Size,Index,F),
+	find_or_insert(Keys, Index, Size, N, Vals, Key, NewVal, Hash).
+
+find_or_insert(Keys, Index, Size, N, Vals, Key, NewVal, Hash) :-
+	array_element(Keys, Index, El),
+	(
+	    var(El)
+	->
+	    add_element(Keys, Index, Size, N, Vals, Key, NewVal, Hash)
+	;
+	    El == Key
+	->
+	     % do rb_update
+	    array_element(Vals, Index, Mutable),
+	    update_mutable(NewVal, Mutable)
+	;
+	    I1 is (Index+1) mod Size,
+	    find_or_insert(Keys, I1, Size, N, Vals, Key, NewVal, Hash)
+	).
+
+add_element(Keys, Index, Size, N, Vals, Key, NewVal, Hash) :-
+	get_mutable(NEls, N),
+	NN is NEls+1,
+	update_mutable(NN, N),
+	(
+	    NN > 3*Size/4
+	->
+	    expand_array(Key, NewVal, Hash)
+	;
+	    array_element(Keys, Index, Key),
+	    update_mutable(NN, N),
+	    array_element(Vals, Index, Mutable),
+	    create_mutable(NewVal, Mutable)
+	).
+
+expand_array(Key, NewVal, Hash) :-
+	Hash = hash(Keys, Vals, Size, _, F),
+	new_size(Size, NewSize),
+	array(NewKeys, NewSize),
+	array(NewVals, NewSize),
+	copy_hash_table(Size, Keys, Vals, F, NewSize, NewKeys, NewVals),
+	setarg(1, Hash, NewKeys),
+	setarg(2, Hash, NewVals),
+	setarg(3, Hash, NewSize),
+	create_mutable(NewVal, Mut),
+	insert_el(Key, Mut, NewSize, F, NewKeys, NewVals).
+
+new_size(Size, NewSize) :-
+	Size > 1048576, !,
+	NewSize is Size+1048576.
+new_size(Size, NewSize) :-
+	NewSize is Size*2.
+
+copy_hash_table(0, _, _, _, _, _, _) :- !.
+copy_hash_table(I1, Keys, Vals, F, Size, NewKeys, NewVals) :-
+	I is I1-1,
+	array_element(Keys, I, Key),
+	nonvar(Key), !,
+	array_element(Vals, I, Val),
+	insert_el(Key, Val, Size, F, NewKeys, NewVals),
+	copy_hash_table(I, Keys, Vals, F, Size, NewKeys, NewVals).
+copy_hash_table(I1, Keys, Vals, F, Size, NewKeys, NewVals) :-
+	I is I1-1,
+	copy_hash_table(I, Keys, Vals, F, Size, NewKeys, NewVals).
+
+insert_el(Key, Val, Size, F, NewKeys, NewVals) :-
+	hash_f(Key,Size,Index, F),
+	find_free(Index, Size, NewKeys, TrueIndex),
+	array_element(NewKeys, TrueIndex, Key),
+	array_element(NewVals, TrueIndex, Val).
+
+find_free(Index, Size, Keys, NewIndex) :-
+	array_element(Keys, Index, El),
+	(
+	    var(El)
+	->
+	    NewIndex = Index
+	;
+	    I1 is (Index+1) mod Size,
+	    find_free(I1, Keys, NewIndex)
+	).
+
+hash_f(Key, Size, Index, F) :-
+	var(F), !,
+	term_hash(Key,-1,Size,Index).
+hash_f(Key, Size, Index, F) :-
+	call(F, Key, Size, Index).
+