1. A computing system comprising: a processing unit; and one or more computer storage media having computer readable instructions stored thereon that, when executed by the processing unit, cause the processing unit to: build a reusable expression graph using a parameter node as a leaf node that acts as a placeholder, wherein the reusable expression graph represents an expression; bind the parameter node to a bindable term such that the parameter node acts act as a proxy for the bindable term, the bindable term comprising another expression that contains a plurality of hard values; and evaluate the expression using the bindable term comprising the another expression that contains the plurality of hard values.