+(define (unregister-components entity components clist)
+ (cond ((null? components) clist)
+ (else
+ (let* ((type (car components))
+ (elist (lset-difference eq? (assoc-ref clist type) (list entity))))
+ (unregister-components entity (cdr components)
+ (cond ((null? elist)
+ (assoc-remove! clist type))
+ (else
+ (assoc-set! clist type elist))))))))
+
+(define (new-entity . new-components)
+ (lambda (entities components)
+ (let ((key (gensym))
+ (nc (normalize-components new-components)))
+ (values
+ (acons key nc entities)
+ (register-components key
+ (map (lambda (c) (car c)) nc)
+ components)
+ key))))
+
+(define (remove-entity key)
+ (lambda (entities components)
+ (let ((clist (map (lambda (c) (car c)) (assoc-ref entities key))))
+ (values
+ (assoc-remove! entities key)
+ (unregister-components key clist components)))))
+
+(define (set-entity key . new-components)
+ (lambda (entities components)
+ (let* ((nc (normalize-components new-components))
+ (clist (map (lambda (c) (car c)) (assoc-ref entities key)))
+ (nclist (map (lambda (c) (car c)) nc)))
+ (values
+ (assoc-set! entities key nc)
+ (register-components key (lset-difference eq? nclist clist)
+ (unregister-components key (lset-difference eq? clist nclist) components))))))
+
+(define (set-entity-components key . new-components)
+ (lambda (entities components)
+ (let ((nc (normalize-components new-components))
+ (clist (alist-copy (assoc-ref entities key))))
+ (for-each
+ (lambda (c)
+ (assoc-set! clist (car c) (cdr c)))
+ nc)
+ (values
+ (assoc-set! entities key clist)
+ (register-components key (map (lambda (c) (car c)) nc) components)))))
+
+(define (remove-entity-components key . old-components)
+ (lambda (entities components)
+ (let ((clist (alist-copy (assoc-ref entities key))))
+ (for-each
+ (lambda (c)
+ (assoc-remove! clist c))
+ old-components)
+ (values
+ (assoc-set! entities key clist)
+ (unregister-components key old-components components)))))
+
+(define (modify-entities changes entities components)
+ (cond ((null? changes)
+ (values entities components))
+ (else
+ (receive (e c) ((car changes) entities components)
+ (modify-entities (cdr changes) e c)))))
+
+(export new-entity
+ remove-entity
+ set-entity
+ set-entity-components
+ remove-entity-components
+ modify-entities)