Escher is a general-purpose, declarative programming language that integrates the best features of both functional and logic programming languages. It has types and modules, higher-order and meta-programming facilities, concurrency, and declarative input/output. The main design aim is to combine in a practical and comprehensive way the best ideas of existing functional and logic languages, such as Haskell and Godel. In fact, Escher uses the Haskell syntax and is most straightforwardly understood as an extension of Haskell. Consequently, this paper discusses Escher from this perspective. It provides an introduction to the Escher language, concentrating largely on the issue of programming style and the Escher programming idioms not provided by Haskell. Also the extra mechanisms needed to support these idioms are discussed.

Go! is a multi-paradigm programming language that is oriented to the needs of programming secure, production quality, agent based applications. It is multi-threaded, strongly typed and higher order (in the functional programming sense). It has relation, function and action procedure definitions. Threads execute action procedures, calling functions and querying relations as need be. Threads in different agents communicate and coordinate using asynchronous messages. Threads within the same agent can also use shared dynamic relations acting as Linda-style tuple stores. In this paper we introduce the essential features of Go!. We then illustrate them by programming a simple multi-agent application comprising hybrid reactive/deliberative agents interacting in a simulated ballroom. The dancer agents negotiate to enter into joint commitments to dance a particular dance (e.g. polka) they both desire. When the dance is announced, they dance together. The agents ’ reactive and deliberative components are concurrently executing threads which communicate and coordinate using belief, desire and intention memory stores. We believe such a multi-threaded agent architecture represents a powerful and natural style of agent implementation, for which Go! is well suited. 1