About

This crate provides a PEG parser with the following features:

• Support for left recursion
• Adaptation: The grammar can be changed dynamically during parsing

This crate is under heavy development and not yet ready to be used in production code.

Example

This defines the grammar of a simple arithmetic language, and support to adapt the language:

rule start = block;
rule block {
    b <- "grammar" "{" g:grammar(prule_action) "}" ";" b:#adapt(g, block);
    s :: b <- s:stmt ";" b:block;
    [] <- "";
}

rule stmt {
    Let(e) <- "let" e:expr;
    Do() <- "do";
}

rule expr {
    group additive {
        Add(x, y) <- x:#next "+" y:#this;
    }
    group multiplicative {
        Mul(x, y) <- x:#next "*" y:#this;
    }
    group base {
        Block(b) <- "(" b:block ")";
        UnaryMinus(v) <- "-" v:#this;
        Num(n) <- n:#str([0-9]*);
    }
}

rule layout = [' ' | '\n'];

Example programs in this language:

1 * 2 + -3

grammar {
    rule expr {
        group additive {
            1 + (-2) <- x:#next "-" y:#this;
        }
    }
};
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