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private pos = 0;
private tokens: string[] = [];
private variables: Record<string, number>;
constructor(private expression: string, variables: Record<string, number> = {}) {
this.variables = {};
for (const [key, value] of Object.entries(variables)) {
this.variables[key.toLowerCase()] = value;
}
this.tokenize();
}
private tokenize() {
// Regex for: functions/words, numbers, operators, parens, comma
const regex = /([a-z][a-z0-9]*)|([0-9]+(?:\.[0-9]+)?)|(\+|-|\*|\/|\^|\(|\)|,)|(\s+)/gi;
let match;
while ((match = regex.exec(this.expression)) !== null) {
// Group 1: Identifier
// Group 2: Number
// Group 3: Operator/Punctuation
// Group 4: Whitespace (skip)
if (match[4]) continue;
this.tokens.push(match[0]);
}
}
evaluate(): number {
this.pos = 0;
const result = this.parseExpression();
if (this.pos < this.tokens.length) {
throw new Error("Unexpected token at end of expression");
}
return result;
}
private parseExpression(): number {
let left = this.parseTerm();
while (this.match("+") || this.match("-")) {
const op = this.previous();
const right = this.parseTerm();
if (op === "+") left += right;
else left -= right;
}
return left;
}
private parseTerm(): number {
let left = this.parseFactor();
while (this.match("*") || this.match("/")) {
const op = this.previous();
const right = this.parseFactor();
if (op === "*") left *= right;
else {
if (right === 0) throw new Error("Division by zero");
left /= right;
}
}
return left;
}
private parseFactor(): number {
return this.parsePower();
// Power handles its own precedence usually higher than mul/div.
// Standard precedence: ^ > * / > + -
}
private parsePower(): number {
let left = this.parsePrimary();
if (this.match("^")) {
const right = this.parsePower(); // Right associative.
left = Math.pow(left, right);
}
return left;
}
private parsePrimary(): number {
if (this.match("(")) {
const expr = this.parseExpression();
if (!this.match(")")) throw new Error("Expected ')'");
return expr;
}
if (this.isNumber()) {
return parseFloat(this.advance());
}
if (this.isIdentifier()) {
const name = this.advance().toLowerCase();
if (this.match("(")) {
if (this.isTrigFunction(name)) {
return this.parseTrigCall(name);
}
const args: number[] = [];
if (!this.check(")")) {
do {
args.push(this.parseExpression());
} while (this.match(","));
}
if (!this.match(")")) throw new Error("Expected ')' after arguments");
return this.callFunction(name, args);
} else {
if (Object.prototype.hasOwnProperty.call(this.variables, name)) {
return this.variables[name];
}
// Constants
if (name === "pi") return Math.PI;
if (name === "e") return Math.E;
if (name === "phi") return (1 + Math.sqrt(5)) / 2;
throw new Error(`Unknown variable or function: ${name}`);
}
}
if (this.match("-")) {
return -this.parsePrimary();
}
if (this.match("+")) {
return this.parsePrimary();
}
throw new Error(`Unexpected token: ${this.peek()}`);
}
private callFunction(name: string, args: number[]): number {
switch (name) {
case "sin":
return Math.sin(this.checkArgs(name, args, 1));
case "cos":
return Math.cos(this.checkArgs(name, args, 1));
case "tan":
return Math.tan(this.checkArgs(name, args, 1));
case "tanh":
return Math.tanh(this.checkArgs(name, args, 1));
case "tanh2":
return Math.atan2(
this.checkArgs(name, args, 2, 0),
this.checkArgs(name, args, 2, 1)
);
case "pow":
return Math.pow(
this.checkArgs(name, args, 2, 0),
this.checkArgs(name, args, 2, 1)
);
case "sqrt":
return Math.sqrt(this.checkArgs(name, args, 1));
case "cbrt":
return Math.cbrt(this.checkArgs(name, args, 1));
case "log":
return (
Math.log(this.checkArgs(name, args, 2, 0)) /
Math.log(this.checkArgs(name, args, 2, 1))
);
default:
throw new Error(`Unknown function: ${name}`);
}
}
private parseTrigCall(name: string): number {
const angle = this.parseExpression();
let unit: "rad" | "deg" = "rad";
if (this.match(",")) {
if (!this.isIdentifier()) throw new Error(`Expected angle unit for ${name}()`);
const token = this.advance().toLowerCase();
unit = this.parseAngleUnit(token);
}
if (!this.match(")")) throw new Error("Expected ')' after arguments");
const radians = unit === "deg" ? (angle * Math.PI) / 180 : angle;
switch (name) {
case "sin":
return Math.sin(radians);
case "cos":
return Math.cos(radians);
case "tan":
return Math.tan(radians);
default:
throw new Error(`Unknown trigonometric function: ${name}`);
}
}
private isTrigFunction(name: string): boolean {
return name === "sin" || name === "cos" || name === "tan";
}
private parseAngleUnit(token: string): "rad" | "deg" {
if (token === "d" || token === "deg" || token === "degree" || token === "degrees") return "deg";
if (token === "r" || token === "rad" || token === "radian" || token === "radians") return "rad";
throw new Error(`Unknown angle unit: ${token}`);
}
private checkArgs(name: string, args: number[], count: number, index: number = 0): number {
if (args.length !== count) throw new Error(`Function '${name}' expects ${count} arguments`);
return args[index];
}
private peek(): string {
return this.tokens[this.pos];
}
private previous(): string {
return this.tokens[this.pos - 1];
}
private advance(): string {
if (!this.isAtEnd()) this.pos++;
return this.previous();
}
private isAtEnd(): boolean {
return this.pos >= this.tokens.length;
}
private match(expected: string): boolean {
if (this.check(expected)) {
this.advance();
return true;
}
return false;
}
private check(expected: string): boolean {
if (this.isAtEnd()) return false;
return this.peek() === expected;
}
private isNumber(): boolean {
if (this.isAtEnd()) return false;
return /^[0-9]+(\.[0-9]+)?$/.test(this.peek());
}
private isIdentifier(): boolean {
if (this.isAtEnd()) return false;
return /^[a-z][a-z0-9]*$/i.test(this.peek());
}
}
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