Toward a Calculus of Signatures

Norman Ramsey

The designers of languages such as Standard ML and Objective Caml have paid much attention to mechanisms for building modules from other modules. Both the underlying semantics and the expressive power have been well crafted. It is surprising then, that the the mechanisms used to build interfaces (signatures) from other interfaces are so impoverished. Signatures languages could be improved by borrowing ideas from the design of abstract data types, especially of sets. This note presents a few examples from real programs, which may convince readers that the shortcomings are real and that the proposed improvements really would help. The note closes with a brief syntactic proposal, which has not yet been fleshed out with semantics.

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