initial commit

modules/lexer.js

@@ -0,0 +1,24 @@
+function tokenize(expr) {
+	// NOTE: not handling whitespace
+	// NOTE: currently ends early if string doesn't match token
+	// FIXME: need to handle unary minus (e.g. on parentheses)
+	const regexp = /-?[0-9]+|[-+*/^]|\(|\)/gy;
+	const matches = expr.matchAll(regexp);
+	
+	const tokens = [];
+	for (const match of matches) {
+		if (/[0-9]+/.test(match[0])) {
+			tokens.push(BigInt(match[0]));
+		} else if (/[-+*^/]/.test(match[0])) {
+			tokens.push(match[0])
+		} else if (match[0] == "(") {
+			tokens.push("(");
+		} else if (match[0] == ")") {
+			tokens.push(")");
+		}
+	}
+
+	return tokens;
+}
+
+export { tokenize };

modules/parser.js

@@ -0,0 +1,69 @@
+function isLeftAssociative(op) {
+	return op === "+" || op === "-" || op === "*" || op === "/";
+}
+
+function popOps(opstack, queue, op) {
+	const prec = {"+": 1, "-": 1, "*": 2, "/": 2, "^": 3}
+	while (true) {
+		const op2 = opstack.at(-1);
+		if (op2 === undefined) {
+			break;
+		} else if (op2 === "(") {
+			break;
+		}
+
+		if ((prec[op2] > prec[op]) || (prec[op2] === prec[op] && isLeftAssociative(op))) {
+			opstack.pop();
+			queue.push(op2);
+		} else {
+			break;
+		}
+	}
+
+	opstack.push(op);
+}
+
+function popBetweenParens(opstack, queue) {
+	while (opstack.at(-1) !== "(") {
+		if (opstack.length === 0) {
+			throw new Error("mismatched parentheses");
+		}
+
+		const op = opstack.pop();
+		queue.push(op);
+	}
+
+	opstack.pop();
+}
+
+function empty(opstack, queue) {
+	while (opstack.length !== 0) {
+		const op = opstack.pop();
+		if (op === "(") {
+			throw new Error("mismatched parentheses");
+		}
+
+		queue.push(op);
+	}
+}
+
+function shunt(tokens) {
+	const queue = [];
+	const opstack = [];
+	for (const token of tokens) {
+		if (typeof token === "bigint") {
+			queue.push(token);
+		} else if (/[-+*/^]/.test(token)) {
+			popOps(opstack, queue, token);
+		} else if (token === "(") {
+			opstack.push(token);
+		} else if (token === ")") {
+			popBetweenParens(opstack, queue);
+		}
+	}
+
+	empty(opstack, queue);
+	return queue;
+}
+
+export { shunt };