Category Archives: PL zoo

The new and improved Programming languages zoo

It is my pleasure to announce the new and improved Programming languages Zoo, a potpourri of miniature but fully functioning programming language implementations. The new zoo has a decent web site, it is now hosted on GitHub, and the source code was cleaned up. Many thanks to Matija Pretnar for all the work.

The purpose of the zoo is to demonstrate design and implementation techniques, from dirty practical details to lofty theoretical considerations:

  • functional, declarative, object-oriented, and procedural languages
  • source code parsing with a parser generator
  • recording of source code positions
  • pretty-printing of values
  • interactive shell (REPL) and non-interactive file processing
  • untyped, statically and dynamically typed languages
  • type checking and type inference
  • subtyping, parametric polymorphism, and other kinds of type systems
  • eager and lazy evaluation strategies
  • recursive definitions
  • exceptions
  • interpreters and compilers
  • abstract machine

There is still a lot of room for improvement and new languages. Contributions are welcome!



I have aded to the PL Zoo a mini prolog interpreter. It really is minimalistic, as it only handles pure Horn clauses. There is no arithmetic, lists, cuts, or disjunctions. Nevertheless, it ought to be possible to write a miniml interpreter in it… If anyone does it, please send me the code!

A toy call-by-push-value language

I have added two new languages to the PL Zoo. The minor addition is miniml+error, which is just MiniML with an error exception (raised by division by 0) that cannot be caught. The purpose is to demonstrate handling of fatal errors during runtime. The more interesting new animal is levy (written by Matija Pretnar and myself), an implementation of Paul Levy’s call-by-push-value language. If you only know about Haskell’s call-by-name and ML’s call-by-value, I invite you to learn about call-by-push-value. Start by reading Paul’s FAQ.

An object-oriented language Boa

I have added another language, called Boa, to the Programming Languages Zoo. It is an object-oriented language with the following features:

  • integers and booleans as base types,
  • first-class functions,
  • dynamically typed,
  • objects are extensible records with mutable fields,
  • there are no classes, instead we can define “prototype” objects and extend them
    to create instances.

Continue reading An object-oriented language Boa