Typed functional programming has the perspective that types are like propositions and their values are proofs of that proposition. For example, the product type A * B encodes logical conjunction, and having a pair with its first element of type A and its second element of type B "proves" the type signature A * B. Similarly, the NonEmpty type encodes the property that at least one element exists. This way, the program is "correct by construction."

This types-are-propositions persoective is called the Curry-Howard correspondence, and it relates to constructive mathematics (wherein all proofs must provide an algorithm for finding a "witness" object satisfying the desired property).