15. A computer-readable memory device or storage device storing a reusable expression graph, the reusable expression graph comprising: an operator node containing an operator; a first parameter node that acts as a first placeholder; and a second parameter node that is joined to the first parameter node by the operator node, wherein the first parameter node comprises at least one operator and at least one operand.
20. The computer-readable memory device or storage device of claim 15 , further storing computer readable instructions which, when executed by a processing unit of a computing device, cause the processing unit to perform acts comprising: at a first time, evaluating an expression represented by the reusable expression graph by evaluating the at least one operator and the at least one operand; binding the first parameter node to a different operator and a different operand; and at a second time, evaluating the expression represented by the reusable expression graph by evaluating the different operator and the different operand instead of the at least one operator and the at least one operand without rebuilding an entirety of the expression.