Zelkova

Like Elm, but different species.

Zelkova is my attempt to understand how one could build a functional programming language compiling to web assembly. It is strongly inspired by Elm, with some Haskell addition here and there.

Do not expect any production-level code here, I'm just trying to understand how a compiler works :)

References

Here is a list of resources I consulted while working on this project.

Articles, Documentation and Source Code

• http://dev.stephendiehl.com/fun/index.html

• https://github.com/RustPython/RustPython/blob/master/parser/src/python.lalrpop

• https://github.com/gluon-lang/gluon/blob/master/base/src/ast.rs

• https://github.com/gluon-lang/gluon/blob/master/parser/src/grammar.lalrpop

• http://smallcultfollowing.com/babysteps/blog/2016/03/02/nice-errors-in-lalrpop/

• https://github.com/lalrpop/lalrpop/issues/67

• https://github.com/elm/compiler/blob/master/compiler/src/Parse/

• https://github.com/elm/compiler/blob/master/compiler/src/AST/Source.hs

• https://elm-lang.org/docs/syntax

• https://github.com/tcr/rust-hindley-milner/blob/master/src/lib.rs

• https://github.com/0b01/tensorscript/tree/master/trsc/src/typing

• https://rickyhan.com/jekyll/update/2018/05/26/hindley-milner-tutorial-rust.html#

• Wand algorithm is a simpler version of Hindley-Milner (different trade off though)

Papers & Books

• The Hindley-Milner Type Inference Algorithm by Ian Grant
• Generalizing Hindley-Milner Type Inference Algorithms by Bastiaan Heeren, Jurriaan Hage and Doaitse Swierstra
• Hindley-Milner Elaboration in Applicative Style (Functional pearl) by François Pottier
• Principled Parsing for Indentation-Sensitive Languages by Michael D. Adams
• Extensible records with scoped labels by Daan Leijen1
• The Essence of ML Type Inference by Pottier and Rémy (Advanced Topics in Types and Programming Languages) 1
• Types and Programming Languages by Benjamin C. Pierce

1 The Elm compiler (0.19) is based/inspired by those papers and books.

Finding cycles

• https://www.cs.tufts.edu/comp/150GA/homeworks/hw1/Johnson%2075.PDF
• https://www.youtube.com/watch?v=johyrWospv0 (nice explanation of above paper)

The above references ended up unused because of the amazing petgraph library.

Documentation

The language itself is specified under docs/spec/, one chapter per file, starting from that directory's index. It is normative — it describes Zelkova as designed, not just what the compiler happens to accept today — and every code example in it is checked against the compiler by cargo test --test spec, so a chapter that drifts from the compiler is a red test rather than a stale sentence. It is published, alongside a landing page and the rendered rustdoc, at francois.monniot.eu/zelkova-lang/.

cargo doc documents the compiler's own Rust, not the language — that's the rustdoc published above. docs/tickets/ is the compiler's work log, not documentation for someone writing Zelkova, and stays unpublished; read it on GitHub.

• Greg Wilson has some idea of what a community need, maybe we can use some of them.