Concurrency-related bugs, such as race conditions and deadlocks, are some of the hardest bugs to isolate, reproduce, understand and fix. Even Erlang programs can suffer from such bugs, for example when messages arrive in unexpected orders or shared resources (e.g. ETS tables) are accessed concurrently. In this workshop I will demonstrate how developers of all levels can use Concuerror, a testing and verification tool for Erlang programs, to automatically detect, isolate and understand concurrency-related errors in their code and explain how the tool can ultimately prove the absence of such errors. I'll also share experiences from two industrial applications of Concuerror in verifying interesting aspects of distributed algorithms.

Let's Lens presents a series of exercises, in a similar format to the Data61 functional programming course material. The subject of the exercises is around the concept of lenses, initially proposed by Foster et al., to solve the view-update problem of relational databases.

The theories around lenses have been advanced significantly in recent years, resulting in a library, implemented in Haskell, called lens.

This workshop will take you through the basic definition of the lens data structure and its related structures such as traversals and prisms. Following this we implement some of the low-level lens library, then go on to discuss and solve a practical problem that uses all of these structures.

1. Motivation/Problem statement: Lifecycle of a GraphQL query
2. Design Goals
3. Why Haskell
4. Compiler implementation details:
   1. Fast GraphQL parsing with parser combinators
   2. Modelling and manipulating the GraphQL AST with algebraic data types
   3. Software Transactional Memory: Concurrency constructs for scaling GraphQL subscriptions
5. Summary with performance benchmarks