try again

ExampleApps.nix

@@ -19,13 +19,16 @@
             -I src -I include \
             -Wall \
             -o $name 
-            ''; 
+            '';
+
+        outputs = [ "out" "headers" ];
 
         installPhase = ''
             mkdir -p $out/bin
             cp $name $out/bin
 
-            cp include -r $out
+            mkdir $headers
+            cp include -r $headers
         '';
 
     };