1 files changed, 32 insertions, 26 deletions
diff --git a/src/inventory.lisp b/src/inventory.lisp
index 17c02e7..429f666 100644
--- a/src/inventory.lisp
+++ b/src/inventory.lisp
@@ -1,6 +1,7 @@
 (defpackage inventory
   (:use :cl)
-  (:export :inventory
+  (:export :new-inventory
+		   :filled
 		   :add-item
 		   :remove-item))
 
@@ -15,6 +16,10 @@
    (items :initform '()
     	  :accessor items)))
 
+(defun new-inventory (size)
+  (when (> size 0)
+	(make-instance 'inventory :size size)))
+
 (defmethod find-item ((inv inventory) name)
   (with-slots (items) inv
 	(find-if
@@ -31,32 +36,33 @@
 
 (defmethod add-item ((inv inventory) item quantity)
   ;; add <quantity> of <item> to inventory
-  (with-slots (size filled items) inv
-	(when (> size (+ filled quantity))
-	  (let* ((old-item
-			  (find-item inv (commodities:name item)))
-			 (qt (if old-item
-					 (progn
-					   (delete-item inv old-item)
-					   (+ quantity (cdr old-item)))
-					 quantity)))
-		(prog1
-		  (setq filled (+ filled qt))
-		  (push (cons item qt)
-				items))))))
+  (when (> quantity 0)
+	(with-slots (size filled items) inv
+	  (when (> size (+ filled quantity))
+		(let* ((old-item
+				(find-item inv (commodities:name item)))
+			   (qt
+				(if old-item
+					(progn
+					  (delete-item inv old-item)
+					  (+ quantity (cdr old-item)))
+					quantity)))
+		  (prog1 (setq filled (+ filled qt))
+			(push (cons item qt)
+				  items)))))))
 
 (defmethod remove-item ((inv inventory) name quantity)
   ;; remove <quantity> of <item> from inventory
   ;; quantity must be positive or zero
-  (assert (>= quantity 0))
-  (with-slots (filled items) inv
-	(let ((item (find-item inv name)))
-	  (when item
-		(delete-item inv item)
-	    (if (< quantity (cdr item))
-			(progn
-			  (add-item inv
-						(car item)
-						(- (cdr item) quantity))
-			  (cons (car item) quantity))
-			item)))))
+  (when (> quantity 0)
+	(with-slots (filled items) inv
+	  (let ((item (find-item inv name)))
+		(when item
+		  (delete-item inv item)
+	      (if (< quantity (cdr item))
+			  (progn
+				(add-item inv
+						  (car item)
+						  (- (cdr item) quantity))
+				(cons (car item) quantity))
+			  item))))))