Structure of the repository

Here we briefly describe the structure of the Helium repository.

Main directories

In the repository we find five directories:

• src: Source code of Helium (described below).
• lib: Standard library of Helium.
• test: Simple Helium programs used by automatic testing. Most of these files are very small and concern only one language feature. You can look into them, to see which language features are implemented.
• examples: More complex and well commented examples of code in Helium.
• other: Other useful resources related to Helium language. Currently only basic modes for Emacs and Vim are provided.

Source code

Here we provide description of the most interesting modules and directories found in the source code

Lang

Module lang contains definitions of all intermediate languages used by the interpreter. By default, the source code is transformed in the following way:

Raw

Raw is a result of parsing.

Flat

Flat is obtained from Raw by compiling out the module system.

Unif

Unif is an intermediate language of type inference.

Explicit

Explicit is an intermediate language where most of the subtyping rules are reified as a coercions. During translation of Unif to Explicit pattern match is compiled out.

Core

Core is similar to Explicit, but coercions without computational meaning are removed. This language corresponds to the calculus lambda HEL described in the Abstracting Algebraic Effects Paper.

Untyped

Untyped is a language where types are erased and effects names are reified as first class values. This language coresponds to untyped calculus from the paper, and is a source language for an abstract machine.

Transform

Transform directory contains all the transformations of code used by Helium. It is divided into subdirectories, by the source language of transformation.

Predef

This directory contains infrastructure for built-in functions as printStr. In Predef.StdExtern you can find a complete list of these functions.