1:- module( store,
    2	[	store_new/1
    3	,	store_add//2
    4	,	store_get//2
    5	,	store_set//2
    6	,	store_upd//3
    7	,	store_apply//2
    8   ,  store_contains//2
    9	]).   10
   11:- meta_predicate store_apply(+,2,+,-).

Supply of references to storage cells

This module provides a sort of store data structure - terms can be added to the store and then accessed using a reference term which is returned by store_add//2.

The type ref(A) denotes the type of store references that point to terms of type A.

All predicates except store_new/1 take store input and output arguments at the end so they can easily be used in a DCG with the store as threaded state variable. */

   27:- use_module(library(rbtrees)).
 store_new(-H:store) is det
Unifies H with an empty store.
   31store_new(store(0,A)) :- rb_empty(A).
 store_add(+V:A, -R:ref(A), +H1:store, -H2:store) is det
Add V to store and return R as a reference to it.
   35store_add(V, N1, store(N1,T1), store(N2,T2)) :- rb_insert_new(T1,N1,V,T2), succ(N1,N2).
 store_get(+R:ref(A), -V:A, +H1:store, -H2:store) is det
Get term refered to by reference R.
   39store_get(Ref, V, store(N,T), store(N,T)) :- rb_lookup(Ref,V,T).
 store_contains(-R:ref(A), -V:A, +H1:store, -H2:store) is nondet
True if store contains A under reference R.
   43store_contains(Ref, V, store(N,T), store(N,T)) :- rb_in(Ref,V,T).
 store_set(+R:ref(A), -V:A, +H1:store, -H2:store) is det
Update the term referred to by R to take the new values V.
   47store_set(Ref, V, store(N,T1), store(N,T2)) :- rb_update(T1,Ref,V,T2).
 store_upd(+R:ref(A), X1:A, X2:A, +H1:store, -H2:store) is det
Unify X1 with the value of R in H1 and replace the value with X2 to get H2. The same effect can be achieved with store_apply//2 but this saves a metacall.
   53store_upd(Ref, V1, V2, store(N,T1), store(N,T2)) :- rb_update(T1,Ref,V1,V2,T2).
 store_apply(+R:ref(A), Op:pred(A,A), +H1:store, -H2:store) is det
Apply binary predicate Op to the term in the store reference by R. The old value is replaced by the new value return by Op in its second argument.
   59store_apply(Ref, Op, store(N,T1), store(N,T2)) :- rb_apply(T1,Ref,Op,T2).
   61user:portray(store(N,_)) :- format('<store|~w items>',[N])