Implementation of an emulator of MIX, a mythical computer invented by Donald Knuth, is used as a case study of the features of the Scala programming language. The developed emulator provides rich opportunities for program debugging, such as tracking intermediate steps of program execution, an opportunity to run a program in the binary or the decimal mode of MIX, verification of correct synchronisation of input/output operations. Such Scala features as cross-compilation, family polymorphism and support for immutable data structures have proved to be useful for implementation of the emulator. The authors of the paper also propose some improvements to these features: flexible definition of family-polymorphic types, integration of family polymorphism with generics, establishing full equivalence between mutating operations on mutable data types and copy-and-modify operations on immutable data types. The emulator is free and open source software available at www.mix-emulator.org.
We consider the problem of comparison of programming languages with respect to their ability to express programmers’ ideas. Our assumption is that the way of programmers’ thinking is reflected in languages used to describe software systems and programs (modelling languages, type theory, pattern languages). We have developed a list of criteria based on these languages and applied it to comparison of a number of widely used programming languages. The obtained result may be used to select a language for a particular task and choose evolution directions of programming languages.