@@ -1,5 +1,42 @@

 (in-package :data-lens.lenses)

+#+fw.dev

+(progn

+  ;; maybe functor implementation

+  (defclass maybe ()

+    ())

+  (defclass just (maybe)

+    ((%v :initarg :value :reader value)))

+  (defclass nothing (maybe)

+    ())

+

+  (defun just (value)

+    (make-instance 'just :value value))

+  (defun nothing (&optional value)

+    (declare (ignore value))

+    (make-instance 'nothing))

+

+  (defgeneric maybe (default value)

+    (:method (default (value just))

+      (value value))

+    (:method (default (value nothing))

+      default))

+

+  (defgeneric maybe-apply (function value)

+    (:method (function (value just))

+      (just (funcall function (value value))))

+    (:method (function (value nothing))

+      value))

+

+  (defmethod print-object ((o just) s)

+    (format s "#.(~s ~s)"

+            'just

+            (value o)))

+

+  (defmethod print-object ((o nothing) s)

+    (format s "#.(~s)"

+            'nothing)))

+

 ;; identity functor, necessary for set and over

 (defclass identity- ()

   ((%v :initarg :value :reader unidentity)))

@@ -173,47 +210,10 @@ contain the new value at the location focused by the lens."

   (defun a-lens (cb)

     (lambda (foo)

       (fw.lu:prog1-bind (new (clone foo))

-        (setf (a new)

-              (funcall cb (a foo))))))

+                        (setf (a new)

+                              (funcall cb (a foo))))))

   (view 'a-lens

         (over 'a-lens '1+

               (set 'a-lens 2

                    (make-instance 'foo :a 1)))) #|

   ==> 3 |#)

-

-#+fw.dev

-(progn

-  ;; maybe functor implementation

-  (defclass maybe ()

-    ())

-  (defclass just (maybe)

-    ((%v :initarg :value :reader value)))

-  (defclass nothing (maybe)

-    ())

-

-  (defun just (value)

-    (make-instance 'just :value value))

-  (defun nothing (&optional value)

-    (declare (ignore value))

-    (make-instance 'nothing))

-

-  (defgeneric maybe (default value)

-    (:method (default (value just))

-      (value value))

-    (:method (default (value nothing))

-      default))

-

-  (defgeneric maybe-apply (function value)

-    (:method (function (value just))

-      (just (funcall function (value value))))

-    (:method (function (value nothing))

-      value))

-

-  (defmethod print-object ((o just) s)

-    (format s "#.(~s ~s)"

-            'just

-            (value o)))

-

-  (defmethod print-object ((o nothing) s)

-    (format s "#.(~s)"

-            'nothing)))