praxis

Praxis is a small, statically typed, garbage-collected language for Advent of Code-style puzzle solving. It is procedural and expression-oriented, it infers essentially every type, and it is built around the three things a puzzle solver spends the evening doing: reading a strange input format, manipulating data, and finding out why the program just fell over.

This crate is the compiler. praxis run parses, type-checks, lowers, JIT-compiles and executes a .px file in one step; there is no build product and nothing lands on disk.

$ cargo install praxis-cli

The binary it installs is called praxis.

A program

var moves = read lines(`{dir:word} {amount:int}`)

var horizontal = 0
var depth = 0

for move in moves {
    match move.dir {
        "forward" => { horizontal = horizontal + move.amount }
        "down" => { depth = depth + move.amount }
        "up" => { depth = depth - move.amount }
        _ => {}
    }
}

out(horizontal * depth)

$ praxis run dive.px --input dive.in
150

No main, no imports, no annotations. read is an expression in the language and the backticked template is a parser the compiler checks and compiles alongside the rest of your program, so moves is a Vec of records with a dir field and an amount field. Nothing declared that record; the template's captures are where it came from.

When it falls over

There are no exceptions and no error handling. An index out of bounds, an integer overflow, a missing key or a template that does not match its input stops the program and hands you the wreckage — not only the locals, but the intermediate values of the expression that faulted, each labelled with the source text it came from. On a terminal you get a prompt instead of an exit code: walk the frames, print expressions against the captured state, then fix the file and reload without losing your input.

praxis check reports the same diagnostics without running anything, and praxis lsp is the language server your editor starts for you.

More

• The Praxis Book covers the language, the input DSL, type inference and the crash debugger.
• The repository.

Praxis was written with large language models against a human design. The repository's README says what that means for the license.

Licensed under either of Apache License 2.0 or the MIT license, at your option.