Conservative Concurrency in Haskell

Abstract. The calculus CHF models Concurrent Haskell extended by concurrent, implicit futures. It is a lambda and process calculus with concurrent threads, monadic concurrent evaluation, and includes a pure functional lambda-calculus PF which comprises data constructors, case-expressions, letrec-expressions, and Haskell’s seq. Our main result is con-servativity of CHF as extension of PF. This allows us to argue that com-piler optimizations and transformations from pure Haskell remain valid in Concurrent Haskell even if it is extended by futures. We also show that conservativity does no longer hold if the extension includes Concurrent Haskell and unsafeInterleaveIO.