Allow for typemaps that reduce everything except null.

src/tink/macro/TypeMap.hx

@@ -8,14 +8,33 @@ import haxe.macro.Type;
 using tink.MacroApi;
 
 class TypeMap<V> extends BalancedTree<Type, V> implements IMap<Type, V> {
-  var follow:Bool;
-  
-  public function new(?noFollow:Bool) {
-    this.follow = noFollow != true;
+  var normalize:Type->Type;
+
+  public function new(?normalize:Type->Type) {
+    this.normalize = switch normalize {
+      case null: function (t) return t.reduce();
+      case fn: fn;
+    }
     super();
   }
-  
+
   override function compare(k1:Type, k2:Type):Int
-    return k1.compare(k2, follow);
-  
+    return normalize(k1).compare(normalize(k2), false);
+
+  static public function noFollow(t:Type)
+    return t;
+
+  static public function keepNull(t:Type):Type
+    return switch t {
+      case TAbstract(_.get() => { name: 'Null', pack: [] }, [t])
+        #if !haxe4 | TType(_.get() => { name: 'Null', pack: []}, [t]) #end
+        :
+        var ct = keepNull(t).toComplex({ direct: true });
+        (macro : Null<$ct>).toType().sure();
+
+      case TLazy(f): keepNull(f());
+      case TType(_, _): keepNull(Context.follow(t, true));
+      default: t;
+    }
+
 }