cfg 0.0.2

cfg

Rust library for manipulating context-free grammars. You can check the documentation here.

Analyzing and modifying grammars

The following features are implemented thus far:

• cycle detection and elimination,
• useless rule detection and elimination,
• grammar binarization,
• nulling rule elimination for binarized grammars,
• FIRST and FOLLOW set computation.

Building grammars

cfg includes an interface that simplifies grammar construction.

Generating symbols

The easiest of generating symbols is with the sym method. The start symbol isn't generated, because it's constant for all grammars.

let mut grammar: Cfg = Cfg::new();
let start = grammar.start_sym();
let (expr, identifier, number,
     plus, multiply, power, l_paren, r_paren, digit) = grammar.sym();

Building grammar rules

Rules have a LHS symbol and zero or more RHS symbols.

grammar.rule(start).rhs([expr])
                   .rhs([identifier, l_paren, expr, r_paren]);

Building sequence rules

Sequence rules have a LHS symbol, a RHS symbol, a range of repetitions, and optional separation. Aside from separation, they closely resemble regular expression repetitions.

grammar.sequence(number).rhs(digit, 1..);

Building precedenced rules

Precedenced rules are the most convenient way to describe operators. Once built, they are immediately rewritten into basic grammar rules, and unique symbols are generated. Operator associativity can be set to Right or Group. It's Left by default.

use cfg::precedence::Associativity::{Right, Group};

grammar.precedenced_rule(expr)
           .rhs([number])
           .rhs([identifier])
           .associativity(Group)
           .rhs([l_paren, expr, r_paren])
       .lower_precedence()
           .associativity(Right)
           .rhs([expr, power, expr])
       .lower_precedence()
           .rhs([expr, multiply, expr])
       .lower_precedence()
           .rhs([expr, plus, expr]);

Using a custom grammar representation

Your grammar type has to implement several traits:

• SymbolSource
• RuleContainer
• ContextFree
• ContextFreeRef
• ContextFreeMut

License

Dual-licensed for compatibility with the Rust project.

Licensed under the Apache License Version 2.0: http://www.apache.org/licenses/LICENSE-2.0, or the MIT license: http://opensource.org/licenses/MIT, at your option.