90 lines
2.0 KiB
JavaScript
90 lines
2.0 KiB
JavaScript
function isLeftAssociative(op) {
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return op === "+" || op === "-" || op === "*" || op === "/";
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}
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function popOps(opstack, queue, op, powInStack) {
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const prec = {"+": 1, "-": 1, "*": 2, "/": 2, "^": 3}
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while (opstack.length > 0) {
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const op2 = opstack.at(-1);
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if (op2 === "(") {
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break;
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}
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if ((prec[op2] > prec[op]) || (prec[op2] === prec[op] && isLeftAssociative(op))) {
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opstack.pop();
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queue.push(op2);
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if (op2 === "^") {
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powInStack = false;
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}
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} else {
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break;
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}
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}
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// practically, we want 2^(3+4) mod 7 to evaluate to 2^7 mod 7 = 2
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// however, since our operators are all modular, this would instead
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// evaluate as 2^0 mod 7 = 1
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// rather than complicate things by evaluating exponent expressions
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// normally instead of modularly (and consequently needing to deal with
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// fractions) we simply require exponents to be integers
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if (powInStack) {
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throw new Error("exponent must be an integer, not an expression");
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}
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}
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function popBetweenParens(opstack, queue, powInStack) {
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while (opstack.at(-1) !== "(") {
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if (opstack.length === 0) {
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throw new Error("mismatched parentheses");
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}
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const op = opstack.pop();
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if (op === "^") {
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powInStack = false;
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}
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queue.push(op);
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}
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opstack.pop();
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return powInStack;
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}
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function empty(opstack, queue) {
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while (opstack.length !== 0) {
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const op = opstack.pop();
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if (op === "(") {
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throw new Error("mismatched parentheses");
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}
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queue.push(op);
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}
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}
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function shunt(tokens) {
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const queue = [];
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const opstack = [];
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let powInStack = false;
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for (const token of tokens) {
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if (typeof token === "bigint") {
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queue.push(token);
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} else if (/[-+*/^]/.test(token)) {
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popOps(opstack, queue, token, powInStack);
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powInStack = false;
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opstack.push(token);
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if (token === "^") {
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powInStack = true;
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}
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} else if (token === "(") {
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opstack.push(token);
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} else if (token === ")") {
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powInStack = popBetweenParens(opstack, queue, powInStack);
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}
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}
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empty(opstack, queue);
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return queue;
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}
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export { shunt };
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