propositional/lib/syntax/parse.js

Propositional logic symbolic computation library

"use strict";
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    if (k2 === undefined) k2 = k;
    var desc = Object.getOwnPropertyDescriptor(m, k);
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      desc = { enumerable: true, get: function() { return m[k]; } };
    }
    Object.defineProperty(o, k2, desc);
}) : (function(o, m, k, k2) {
    if (k2 === undefined) k2 = k;
    o[k2] = m[k];
}));
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    Object.defineProperty(o, "default", { enumerable: true, value: v });
}) : function(o, v) {
    o["default"] = v;
});
var __importStar = (this && this.__importStar) || function (mod) {
    if (mod && mod.__esModule) return mod;
    var result = {};
    if (mod != null) for (var k in mod) if (k !== "default" && Object.prototype.hasOwnProperty.call(mod, k)) __createBinding(result, mod, k);
    __setModuleDefault(result, mod);
    return result;
};
Object.defineProperty(exports, "__esModule", { value: true });
exports.parse = void 0;
const token_1 = require("./token");
const AST = __importStar(require("./ast"));
// The parser will assume non-bracketed binary expressions are to be treated as right-associative.
function parse(tokenStream) {
    let currentToken = 0;
    let peek = () => tokenStream[currentToken];
    let previous = () => tokenStream[currentToken - 1];
    let advance = () => tokenStream[currentToken++];
    let check = (type) => currentToken >= tokenStream.length ? false : (peek().type == type);
    let match = (...types) => {
        for (let type of types) {
            if (check(type)) {
                advance();
                return true;
            }
        }
        return false;
    };
    let expect = (type, message) => {
        if (check(type))
            return advance();
        throw Error('[' + (peek()?.lexeme || 'end') + '] ' + message);
    };
    // Grammar implementation
    function expression() {
        return binary();
    }
    function binary() {
        let left = unary();
        while (match(token_1.TokenType.AND, token_1.TokenType.OR, token_1.TokenType.XOR, token_1.TokenType.IF, token_1.TokenType.IFF)) {
            let operator = previous();
            let right = unary();
            left = new AST.BinaryExpression(left, operator, right);
        }
        return left;
    }
    function unary() {
        if (match(token_1.TokenType.NOT)) {
            let operator = previous();
            let right = unary();
            return new AST.UnaryExpression(operator, right);
        }
        return primary();
    }
    function primary() {
        // literals
        if (match(token_1.TokenType.CONSTANT, token_1.TokenType.VARIABLE)) {
            return new AST.Literal(previous());
        }
        // groupings
        if (match(token_1.TokenType.PAREN_L)) {
            let inner = expression();
            expect(token_1.TokenType.PAREN_R, 'unclosed grouping');
            return inner;
        }
        // something else
        let token = peek()?.lexeme;
        if (token) {
            throw Error('Unexpected token ' + token);
        }
        else {
            throw Error('Unexpected end of input');
        }
    }
    let expr = expression();
    if (peek()?.lexeme) {
        throw Error('Unexpected token ' + peek().lexeme);
    }
    return expr;
}
exports.parse = parse;