diff --git a/cli.carp b/cli.carp
index 4117cdb..e1dc397 100644
--- a/cli.carp
+++ b/cli.carp
@@ -46,8 +46,8 @@ manually.
 Once you’re done building your flag structure, you can run `CLI.parse`. It
 will not abort the program on error, instead it will tell you what went wrong
 in a `Result.Error`. If it succeeds, the `Result.Success` contains a `Map` from
-the long flag name to the value (the values are `Maybe`s, since they might be
-optional arguments.")
+the long flag name to the value. The values are not in the map if they are
+unset.")
 (defmodule CLI
   (hidden Type)
   (private Type)
@@ -55,11 +55,16 @@ optional arguments.")
     (Integer [Long])
     (Floating [Double])
     (Str [String])
+    (None [])
   )
 
   (defmodule Type
     (defn = [a b]
       (match @a
+        (None)
+          (match @b
+            (None) true
+            _ false)
         (Integer i)
           (match @b
             (Integer j) (= i j)
@@ -109,6 +114,8 @@ optional arguments.")
       (match x
         (Floating d) d
         _ 0.0))
+
+    (defn zero [] (None))
   )
 
   (hidden Tag)
@@ -228,7 +235,10 @@ optional arguments.")
 
     (defn to-map [m]
       (Array.reduce
-        &(fn [a v] (Map.put a (Pair.a (Pair.a v)) (Pair.b (Pair.b v))))
+        &(fn [a v]
+          (match @(Pair.b (Pair.b v))
+            (Maybe.Just e) (Map.put a (Pair.a (Pair.a v)) &e)
+            (Maybe.Nothing) a))
         {}
         (values m)))
   )
diff --git a/docs/CLI.html b/docs/CLI.html
index 9f83749..c9d4565 100644
--- a/docs/CLI.html
+++ b/docs/CLI.html
@@ -61,10 +61,29 @@ manually.</p>
 <p>Once you’re done building your flag structure, you can run <code>CLI.parse</code>. It
 will not abort the program on error, instead it will tell you what went wrong
 in a <code>Result.Error</code>. If it succeeds, the <code>Result.Success</code> contains a <code>Map</code> from
-the long flag name to the value (the values are <code>Maybe</code>s, since they might be
-optional arguments.</p>
+the long flag name to the value. The values are not in the map if they are
+unset.</p>
 
             </div>
+            <div class="binder">
+                <a class="anchor" href="#(defdynamic CLI.*gensym-counter* 1001)">
+                    <h3 id="(defdynamic CLI.*gensym-counter* 1001)">
+                        (defdynamic CLI.*gensym-counter* 1001)
+                    </h3>
+                </a>
+                <div class="description">
+                    dynamic
+                </div>
+                <p class="sig">
+                    Dynamic
+                </p>
+                <span>
+                    
+                </span>
+                <p class="doc">
+                    
+                </p>
+            </div>
             <div class="binder">
                 <a class="anchor" href="#Option">
                     <h3 id="Option">
@@ -197,7 +216,7 @@ optional arguments.</p>
                     defn
                 </div>
                 <p class="sig">
-                    (λ [(Ref Parser)] (Result (Map String (Maybe Type)) String))
+                    (λ [(Ref Parser)] (Result (Map String Type) String))
                 </p>
                 <pre class="args">
                     (parse p)