panproto-expr-parser

Parses human-written expressions into the panproto-expr AST, and formats them back to text.

What it does

panproto-expr represents expressions as an AST (Expr enum values). This crate is the bridge between that AST and a string you can actually type. It takes a string like \x -> if x > 0 then x * 2 else 0 and produces the corresponding Expr tree, or takes an Expr tree and formats it back to a readable string.

The surface syntax follows Haskell conventions: backslash-lambdas, let/in, case/of with pattern matching, if/then/else, list comprehensions, and record literals. A Pratt precedence climbing algorithm handles operator precedence correctly, so 1 + 2 * 3 parses as 1 + (2 * 3) without requiring explicit parentheses. The pretty-printer is the inverse: it adds parentheses only where needed to preserve the original meaning, so parse(tokenize(pretty_print(expr))) == expr for all well-formed expressions.

The lexer uses logos for fast tokenization and inserts GHC-style layout tokens (Indent/Dedent) so indented blocks work without explicit braces. The parser uses chumsky 1.0.

Quick example

use panproto_expr_parser::{tokenize, parse, pretty_print};

let tokens = tokenize(r#"\x -> x * 2 + 1"#).unwrap();
let expr = parse(&tokens).unwrap();

// Serialize back to canonical surface syntax.
let source = pretty_print(&expr);
assert_eq!(source, r#"\x -> x * 2 + 1"#);

API overview

License

MIT