Algebraic effect handlers, introduced by Plotkin and Power in 2002, are recently gaining in popularity as a purely functional approach to modeling effects. In this article, we give a full overview of practical algebraic effects in the context of a compiled implementation in the Koka language. In particular, we show how algebraic effects generalize over common constructs like exception handling, state, iterators and async-await. We give an effective type inference algorithm based on extensible effect rows using scoped labels, and a direct operational semantics. Finally, we show an efficient compilation scheme to common runtime platforms (like JavaScript) using a type directed selective CPS translation.

Building applications that are responsive and can exploit parallel hardware while remaining simple to write, understand, test, and maintain, poses an important challenge for developers. In particular, it is often desirable to enable various tasks to read or modify shared data concurrently without requiring complicated locking schemes that may throttle concurrency and introduce bugs.We introduce a mechanism that simplifies the parallel execution of different application tasks. Programmers declare what data they wish to share between tasks by using isolation types, and execute tasks concurrently by forking and joining revisions. These revisions are isolated: they read and modify their own private copy of the shared data only. A runtime creates and merges copies automatically, and resolves conflicts deterministically, in a manner declared by the chosen isolation type.To demonstrate the practical viability of our approach, we developed an efficient algorithm and an implementation in the form of a C# library, and used it to parallelize an interactive game application. Our results show that the parallelized game, while simple and very similar to the original sequential game, achieves satisfactory speedups on a multicore processor.

The MLF type system by Le Botlan and Rémy is a natural extension of Hindley-Milner type inference that supports full first-class polymorphism, where types can be of higher-rank and impredicatively instantiated. Even though MLF is theoretically very attractive, it has not seen widespread adoption. We believe that this partly because it is unclear how the rich language of MLF types relate to standard System F types. In this article we give the first type directed translation of MLF terms to System F terms. Based on insight gained from this translation, we also define "Rigid MLF" (MLF = ), a restriction of MLF where all bound values have a System F type. The expressiveness of MLF = is the same as that of boxy types, but MLF = needs fewer annotations and we give a detailed comparison between them.

Domain-specific embedded languages (DSELs) expressed in higher-order, typed (HOT) languages provide a composable framework/or domain-specific abstractions. Such a framework is o] greater utilsty than a collectwn o/stand-alone domain-specific languages. Usually, embedded domain speczfic languages are build on top o] a set o] domain specific primitwe ]unctions that are ultimately implemented using some ]orm o/]oreign ]unction call. We sketch a general design pattern/or embedding chent-server style services into Haskell using a domare specific embedded compiler /or the server's source language. In particular we apply this idea to implement Haskell/DB, a domain specific embdedded compiler that dynamically generates o/SQL queries #ore monad comprehensions, which are then executed on an arbitrary ODBC database server.

MLF is a type system that extends a functional language with impredicative rank-n polymorphism. Type inference remains possible and only in some clearly defined situations, a local type annotation is required. Qualified types are a general concept that can accommodate a wide range of type systems extension, for example, type classes in Haskell. We show how the theory of qualified types can be used seamlessly with the higher-ranked impredicative polymorphism of MLF, and give a solution to the non-trivial problem of evidence translation in the presence of impredicative datatypes.