Custom Effect Shading

[Vaquero]

Could someone please post a simple example that shows how to access the variables for normal, eyevec, viewDir etc. in a custom GLSL fragment shader?
The make-it-all-red sample in the documentation isn't helping:

fragCode = """
void main()
{
    gl_FragColor = vec4(1.0,0.0,0.0,1.0);
}
"""

shader = viz.addShader(frag=fragCode)

That's just TOO simple.