praxis-input-parser

The read DSL of Praxis: template parsing, static validation, result-type synthesis and parser plans.

In Praxis the input parser is part of the language. read is an expression, and what follows it is a small declarative language for the shape of a file:

var input = read sections(
    rules: lines(`{before:int}|{after:int}`),
    updates: lines(csv(int)),
)

Structure goes outside the backticks, where whitespace does not matter; the input's literal text goes inside, where it does. Parsers nest, and the type comes from the parser — input above is a record with a rules field of type Vec[{ before: Int, after: Int }] and an updates field of type Vec[Vec[Int]], and nothing declared it. Getting the shape of the input wrong is therefore a compile error rather than a surprise several hundred lines in.

The DSL keeps its own typed AST and is not lowered into string-splitting calls, which is what lets it be type-checked, hovered over and completed like the rest of the language.

What it covers

• Atomics: int, uint, float, byte, char, digit, word, identifier, text, rest.
• Constructors: lines, sections, csv, ws, sep, grid, matrix, chars, one_of, block, choice, optional, scan, repeated.
• Backtick templates, whose {name:int} captures become record fields.
• validate — static checking, with I0xx diagnostics and did-you-mean suggestions.
• synthesize — the compile-time result type of a parser expression.
• lower_to_plan, ParserPlan — the plan the runtime interprets.

The interpreter that runs a plan against real bytes lives in praxis-runtime.

Part of Praxis

Praxis is a small, statically typed, garbage-collected language for Advent of Code-style puzzles: the input parser is part of the language, types are inferred rather than written, and a program that falls over hands you its state instead of a stack trace.

To use the language, install praxis-cli — it provides the praxis binary. The repository has the book, the design document and the decision records.

This crate is one stage of that compiler, published so the pipeline is inspectable and so praxis-cli can be built from the registry. Its API tracks what the compiler needs and is not a stable platform for outside consumers.

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.