schala/README.md

# Schala - a programming language meta-interpreter

Schala is a Rust framework written to make it easy to create and experiment
with multipl toy programming languages. It provides a cross-language REPL and
provisions for tokenizing text, parsing tokens, evaluating an abstract syntax
tree, and other tasks that are common to all programming languages, as well as sharing state
between multiple programming languages.

Schala is implemented as a Rust library `schala-repl`, which provides a
function `start_repl`, meant to be used as entry point into a common REPL or
non-interactive environment. Clients are expected to invoke `start_repl` with a
vector of programming languages. Individual programming language
implementations are Rust types that implement the
`ProgrammingLanguageInterface` trait and store whatever persistent state is
relevant to that language. 

Run schala with: `cargo run`. This will drop you into a REPL environment.  Type
`:help` for more information, or type in text in any supported programming
language (currently only schala-lang) to evaluate it in the REPL.

## History

Schala started out life as an experiment in writing a Javascript-like
programming language that would never encounter any kind of runtime value
error, but rather always return `null` under any kind of error condition. I had
seen one too many Javascript `Uncaught TypeError: Cannot read property ___ of
undefined` messages, and I was a bit frustrated.  Plus I had always wanted to
write a programming langauge from scratch, and Rust is a fun language to
program in.  Over time I became interested in playing around with other sorts
of programming languages as well, and wanted to make the process as general as
possible.

The name of the project comes from Schala the Princess of Zeal from the 1995
SNES RPG *Chrono Trigger*. I like classic JRPGs and enjoyed the thought of
creating a language name confusingly close to Scala. The naming scheme for
languages implemented with the Schala meta-interpreter is Chrono Trigger
characters.

Schala and languages implemented with it are incomplete alpha software and are
not ready for public release.

## Languages implemented using the meta-interpreter

* The eponymous *Schala* language is a work-in-progress general purpose
  programming language with static typing and algebraic data types. Its design
  goals include having a very straightforward implemenation and being syntactically
  minimal.

* *Maaru* is a very simple dynamically-typed scripting language, with the semantics
    that all runtime errors return a `null` value rather than fail. 

* *Robo* is an experiment in creating a lazy, functional, strongly-typed language
much like Haskell

* *Rukka* is a straightforward LISP implementation

## Reference works

Here's a partial list of resources I've made use of in the process
of learning how to write a programming language.

### General

http://thume.ca/2019/04/18/writing-a-compiler-in-rust/
http://thume.ca/2019/07/14/a-tour-of-metaprogramming-models-for-generics/

### Type-checking
https://skillsmatter.com/skillscasts/10868-inside-the-rust-compiler
https://www.youtube.com/watch?v=il3gD7XMdmA
http://dev.stephendiehl.com/fun/006_hindley_milner.html
https://rust-lang-nursery.github.io/rustc-guide/type-inference.html

https://eli.thegreenplace.net/2018/unification/
https://eli.thegreenplace.net/2018/type-inference/
http://smallcultfollowing.com/babysteps/blog/2017/03/25/unification-in-chalk-part-1/
http://reasonableapproximation.net/2019/05/05/hindley-milner.html
https://rickyhan.com/jekyll/update/2018/05/26/hindley-milner-tutorial-rust.html

### Evaluation
*Understanding Computation*, Tom Stuart, O'Reilly 2013

*Basics of Compiler Design*, Torben Mogensen

### Parsing
http://journal.stuffwithstuff.com/2011/03/19/pratt-parsers-expression-parsing-made-easy/
https://soc.github.io/languages/unified-condition-syntax

[Crafting Interpreters](http://www.craftinginterpreters.com/)

### LLVM
http://blog.ulysse.io/2016/07/03/llvm-getting-started.html

###Rust resources
https://thefullsnack.com/en/rust-for-the-web.html

https://rocket.rs/guide/getting-started/