87 lines
3.5 KiB
Markdown
87 lines
3.5 KiB
Markdown
# Schala - a programming language meta-interpreter
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Schala is a Rust framework written to make it easy to create and experiment
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with toy programming languages. It provides a cross-language REPL and
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provisions for tokenizing text, parsing tokens, evaluating an abstract syntax
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tree, and other tasks that are common to all programming languages.
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Schala is implemented as a Rust library `schala-repl`, which provides a
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function `repl_main` meant to be used as the equivalent of main() for library
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users. This function parses command-line arguments and either runs an interactive
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REPL or interprets a program non-interactively.
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Individual programming language implementations are Rust types that implement
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the `ProgrammingLanguageInterface` trait and store whatever persistent state is
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relevant to that language. The ability to share state between different
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programming languages is in the works.
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## History
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Schala started out life as an experiment in writing a Javascript-like
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programming language that would never encounter any kind of runtime value
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error, but rather always return `null` under any kind of error condition. I had
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seen one too many Javascript `Uncaught TypeError: Cannot read property ___ of
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undefined` messages, and I was a bit frustrated. Plus I had always wanted to
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write a programming langauge from scratch, and Rust is a fun language to
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program in. Over time I became interested in playing around with other sorts
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of programming languages as well, and wanted to make the process as general as
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possible.
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The name of the project comes from Schala the Princess of Zeal from the 1995
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SNES RPG *Chrono Trigger*. I like classic JRPGs and enjoyed the thought of
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creating a language name confusingly close to Scala. The naming scheme for
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languages implemented with the Schala meta-interpreter is Chrono Trigger
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characters.
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Schala is incomplete alpha software and is not ready for public release.
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## Languages implemented using the meta-interpreter
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* The eponymous *Schala* language is an interpreted/compiled scripting langauge,
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designed to be relatively simple, but with a reasonably sophisticated type
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system.
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* *Maaru* was the original Schala (since renamed to free up the name *Schala*
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for the above language), a very simple dynamically-typed scripting language
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such that all possible runtime errors result in null rather than program
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failure.
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* *Robo* is an experiment in creating a lazy, functional, strongly-typed language
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much like Haskell
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* *Rukka* is a straightforward LISP implementation
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## Reference works
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Here's a partial list of resources I've made use of in the process
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of learning how to write a programming language.
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### Type-checking
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https://skillsmatter.com/skillscasts/10868-inside-the-rust-compiler
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https://www.youtube.com/watch?v=il3gD7XMdmA
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http://dev.stephendiehl.com/fun/006_hindley_milner.html
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https://rust-lang-nursery.github.io/rustc-guide/type-inference.html
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https://eli.thegreenplace.net/2018/unification/
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https://eli.thegreenplace.net/2018/type-inference/
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http://smallcultfollowing.com/babysteps/blog/2017/03/25/unification-in-chalk-part-1/
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### Evaluation
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*Understanding Computation*, Tom Stuart, O'Reilly 2013
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*Basics of Compiler Design*, Torben Mogensen
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### Parsing
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http://journal.stuffwithstuff.com/2011/03/19/pratt-parsers-expression-parsing-made-easy/
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https://soc.github.io/languages/unified-condition-syntax
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[Crafting Interpreters](http://www.craftinginterpreters.com/)
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### LLVM
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http://blog.ulysse.io/2016/07/03/llvm-getting-started.html
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###Rust resources
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https://thefullsnack.com/en/rust-for-the-web.html
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https://rocket.rs/guide/getting-started/
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