pegjs/lib/compiler/visitor.js

"use strict";

// Simple AST node visitor builder.
const visitor = {
    build( functions ) {

        function visit( node ) {

            return functions[ node.type ].apply( null, arguments );

        }

        function visitNop() {
            // Do nothing.
        }

        function visitExpression( node ) {

            const extraArgs = Array.prototype.slice.call( arguments, 1 );

            visit.apply( null, [ node.expression ].concat( extraArgs ) );

        }

        function visitChildren( property ) {

            return function visitProperty( node ) {

                const extraArgs = Array.prototype.slice.call( arguments, 1 );

                node[ property ].forEach( child => {

                    visit.apply( null, [ child ].concat( extraArgs ) );

                } );

            };

        }

        const DEFAULT_FUNCTIONS = {
            grammar( node ) {

                const extraArgs = Array.prototype.slice.call( arguments, 1 );

                if ( node.initializer ) {

                    visit.apply( null, [ node.initializer ].concat( extraArgs ) );

                }

                node.rules.forEach( rule => {

                    visit.apply( null, [ rule ].concat( extraArgs ) );

                } );

            },

            initializer: visitNop,
            rule: visitExpression,
            named: visitExpression,
            choice: visitChildren( "alternatives" ),
            action: visitExpression,
            sequence: visitChildren( "elements" ),
            labeled: visitExpression,
            text: visitExpression,
            simple_and: visitExpression,
            simple_not: visitExpression,
            optional: visitExpression,
            zero_or_more: visitExpression,
            one_or_more: visitExpression,
            group: visitExpression,
            semantic_and: visitNop,
            semantic_not: visitNop,
            rule_ref: visitNop,
            literal: visitNop,
            class: visitNop,
            any: visitNop
        };

        Object.keys( DEFAULT_FUNCTIONS ).forEach( type => {

            if ( ! Object.prototype.hasOwnProperty.call( functions, type ) ) {

                functions[ type ] = DEFAULT_FUNCTIONS[ type ];

            }

        } );

        return visit;

    }
};

module.exports = visitor;