I don' think that's possible, since shaders are evaluated at render time only. Many nodes give different results when rendering, so everything containing a texture node, an u- or v- node, an edge blend or a fresnel node will give different results on different pixels of the render. The only cases in which the results can be caclulated are those with simple, nonvariable numbers - and those can easily be entered in the node directly.

What do you exactly want to do with that?

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Sail out to sea and do new things.
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