Modular Monadic Semantics (MMS) is a well-known mechanism for structuring modular denotational semantic definitions for programming languages. The principal attraction of MMS is that families of language constructs can be independently specified and later combined in a mix-and-match fashion to create a complete language semantics. This has proved useful for constructing formal, yet executable, semantics when prototyping languages. In this work we demonstrate that MMS has an additional software engineering benefit. Rather than composing semantics for various language constructs, we can use MMS to compose various differing semantics for the same language constructs. We describe algebra combinators, the principal vehicle for achieving this reuse, along with a series of applications of the technique for common language processing tasks.

Modular monadic semantics (MMS) is a well-known technique for structuring modular denotational semantic definitions. Families of language constructs are independently defined using syntactic functors and semantic algebras that can be combined in a mix-and-match fashion to create complete language definitions. We introduce InterpreterLib, a Haskell library that implements and extends MMS techniques for writing composable analyses. In addition to modular analyses composition, InterpreterLib provides algebra combinators, explicit algebra semantics, preprocessors for boiler plate generation and generic programming techniques adapted to language analysis. The key benefits of these features are reliability, increased code reuse via modularity and the ability to rapidly retarget component analyses.