Simple directional light shader via vert/frag

Could someone provide me with a simple lambert lighting model shader that uses a directional light.
I’d like to use that as a jumping off point to a more complex effect that i’m trying to achieve.

I ask because there are many gaps in my knowledge of shaders in unity, and I keep hitting a wall on the simplest things.

As an aside, I’m simply trying to do per-face lighting on a model, however if I create a surface shader the function ddx / dFdx are not available to me.

However If I create my own vertex/fragment shader I am able to use the dFdx/ddx funcitons, but I lose all the lighting information

I haven’t test run this yet, but it looks pretty solid.

http://kylehalladay.com/all/blog/2013/10/13/Multi-Light-Diffuse.html