Crate bnf

bnf, a library for parsing Backus–Naur form context-free grammars

Inspired by the JavaScript library prettybnf

The code is available on Github

What does a parsable BNF grammar look like?

The following grammar from the Wikipedia page on Backus-Naur form exemplifies a compatible grammar after adding ';' characters to indicate the end of a producion.

<postal-address> ::= <name-part> <street-address> <zip-part>;
 
        <name-part> ::= <personal-part> <last-name> <opt-suffix-part> <EOL>
                    | <personal-part> <name-part>;
 
    <personal-part> ::= <initial> "." | <first-name>;
 
    <street-address> ::= <house-num> <street-name> <opt-apt-num> <EOL>;
 
        <zip-part> ::= <town-name> "," <state-code> <ZIP-code> <EOL>;
 
<opt-suffix-part> ::= "Sr." | "Jr." | <roman-numeral> | "";
    <opt-apt-num> ::= <apt-num> | "";

Output

Take the following grammar to be input to this library's parse function:

<A> ::= <B> | "C";
<B> ::= "D" | "E"; 

The output is a Grammar object representing a tree that looks like this:

Grammar {
    productions: [
        Production {
            lhs: Nonterminal(
                "A"
            ),
            rhs: [
                Expression {
                    terms: [
                        Nonterminal(
                            "B"
                        )
                    ]
                },
                Expression {
                    terms: [
                        Terminal(
                            "C"
                        )
                    ]
                }
            ]
        },
        Production {
            lhs: Nonterminal(
                "B"
            ),
            rhs: [
                Expression {
                    terms: [
                        Terminal(
                            "D"
                        )
                    ]
                },
                Expression {
                    terms: [
                        Terminal(
                            "E"
                        )
                    ]
                }
            ]
        }
    ]
}

Example

extern crate bnf;
 
fn main() {
    let input =
        "<postal-address> ::= <name-part> <street-address> <zip-part>;
 
              <name-part> ::= <personal-part> <last-name> <opt-suffix-part> <EOL>
                            | <personal-part> <name-part>;
 
          <personal-part> ::= <initial> \".\" | <first-name>;
 
         <street-address> ::= <house-num> <street-name> <opt-apt-num> <EOL>;
 
               <zip-part> ::= <town-name> \",\" <state-code> <ZIP-code> <EOL>;
 
        <opt-suffix-part> ::= \"Sr.\" | \"Jr.\" | <roman-numeral> | \"\";
            <opt-apt-num> ::= <apt-num> | \"\";";
 
    let grammar = bnf::parse(input);
    println!("{:#?}", grammar);
}

Modules

node

Functions

parse

Parse a BNF grammer