pegjs/lib/compiler/asts.js

"use strict";

const visitor = require( "./visitor" );

// AST utilities.
const asts = {
    findRule( ast, name ) {

        for ( let i = 0; i < ast.rules.length; i++ ) {

            if ( ast.rules[ i ].name === name ) return ast.rules[ i ];

        }

        return void 0;

    },

    indexOfRule( ast, name ) {

        for ( let i = 0; i < ast.rules.length; i++ ) {

            if ( ast.rules[ i ].name === name ) return i;

        }

        return -1;

    },

    alwaysConsumesOnSuccess( ast, node ) {

        let consumes;

        function consumesTrue() {

            return true;

        }
        function consumesFalse() {

            return false;

        }

        function consumesExpression( node ) {

            return consumes( node.expression );

        }

        consumes = visitor.build( {
            rule: consumesExpression,
            named: consumesExpression,

            choice( node ) {

                return node.alternatives.every( consumes );

            },

            action: consumesExpression,

            sequence( node ) {

                return node.elements.some( consumes );

            },

            labeled: consumesExpression,
            text: consumesExpression,
            simple_and: consumesFalse,
            simple_not: consumesFalse,
            optional: consumesFalse,
            zero_or_more: consumesFalse,
            one_or_more: consumesExpression,
            group: consumesExpression,
            semantic_and: consumesFalse,
            semantic_not: consumesFalse,

            rule_ref( node ) {

                return consumes( asts.findRule( ast, node.name ) );

            },

            literal( node ) {

                return node.value !== "";

            },

            class: consumesTrue,
            any: consumesTrue
        } );

        return consumes( node );

    }
};

module.exports = asts;