Feature request - lazy evaluation of expressions with missing variables

[seime]

Thanks for providing this great library!

I have a use case where multiple expressions with dependencies between them that needs to be solved piece by piece (expression by expression), ie

expression 1: a || b -> store as variable c
expression 2: c || d-> store as variable e

In order to solve expression 1, I need to solve expresssion 2.

However, not all variables will be available, and I would still like to solve the expressions with the variables that are available. Thus the need for lazy evaluation.

For instance in expression 1, if either a or b is available and just one of them is true, I would like expression 1 to evaluate successfully to true. This again would let me evaluate expression 2 without the need for d to be present.