In this repository we implement the interaction nets language first described by Yves Lafont in 1989 [1]. Interaction nets are a model of computation like the lambda calculus, but even lower level. Cellular automata, rewrite systems and Turing machines can all be considered as a special case of interaction nets [2]. Another nice property of interaction nets is that they can easily be mapped onto conventional computer hardware without the need of a garbage collector [1].

In this project we implemented a very basic compiler for interaction nets. We have tried to adhere as much as possible to the proposal of Lafont in his original paper [1], but for some parts we took inspiration from a later paper by Ian Mackie [3] especially for the initial net definition.

This project contains the following Rascal modules:

• AST contains the abstract syntax tree.
• CST2AST contains the transformation from a concrete syntax tree to an abstract syntax tree.
• Check contains a static semantics checker.
• Compile contains a compiler that translates an abstract syntax tree to C code.
• Eval contains an evaluator that can run interaction nets without compiling.
• IDE hooks into eclipse to show warnings and errors and compiles interaction net files.
• Syntax contains the concrete syntax specification.

This project contains the following example interaction net files:

• ackermann.int contains an implementation of the Ackermann function with unary arithmetic. The initial net definition calculates A(3, 8), which is too large for the evaluator, but the compiled version can run in reasonable time.
• difference-lists.int contains an implementation of difference lists [5]. The initial net definition calculates appending a difference list containing [P,O,P] and another difference list containing [L] to eachother.
• lists.int contains an implementation for lists. The initial net definition calculates appending a list containing [P,O,P] and another list containing [L] to eachother.
• parsing.int contains a simple expression parser that can parse a stream of the number 1 and the infix symbol P (for plus) into a tree based abstract syntax. The initial net definition parses the stream (1, P, 1, End) into the abstract tree P(1, 1). It should be noted that no error handeling is implemented. The interaction 'End >< Parse' is not implemented. A malformed input stream can cause undefined behavior.
• simple.int contains one of the simplest possible interaction nets. It only has a single interaction rule. The initial net definition defines a net that performs the single interaction rule.
• test.int is a test script used during development for testing.
• turnstile.int contains a demonstration of an infinitely reducing interaction net. The initial net definition will execute indefinitely.
• unary-arithmetics.int contains an implementation of unary arithmetic, including addition, multiplication and finding the maximum of two numbers. The initial net definition calculates the expression max(2 * 3, 2 + 3).
• errors.int contains all possible warnings and errors implemented in the semantics checker.

Most of these example interaction net files are based on the examples in the original paper by Lafont [1].

Currently, the compiled programs do not have any input or output capabilities. They only print the interactions that occur to the standard output. This can easily be changed manually after generating the C source files.

• [1] Lafont, Yves. "Interaction nets." Proceedings of the 17th ACM SIGPLAN-SIGACT symposium on Principles of programming languages. ACM, 1989.
• [2] Lafont, Yves. "Interaction combinators." Information and Computation 137.1 (1997): 69-101.
• [3] Mackie, Ian. "Towards a programming language for interaction nets." Electronic Notes in Theoretical Computer Science 127.5 (2005): 133-151.
• [4] Wikipedia contributors. "Ackermann function." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 10 Sep. 2019. Web. 20 Jan. 2020.
• [5] "Difference list." HaskellWiki, . 1 Aug 2018, 16:40 UTC. 20 Jan 2020, 18:25 https://wiki.haskell.org/index.php?title=Difference_list&oldid=62571.