Built-in Functions

Adding Built-in Functions

Real languages come with built-in functions. Let's add three:

Parsing Function Calls

When we see an identifier followed by (, it's a function call:

parseFactor() {
    if (this.peek().type === "IDENT") {
        const name = this.advance().value;
        if (this.peek().type === "LPAREN") {
            this.advance(); // consume (
            const args = [];
            if (this.peek().type !== "RPAREN") {
                args.push(this.parseExpr());
                while (this.peek().type === "COMMA") {
                    this.advance();
                    args.push(this.parseExpr());
                }
            }
            this.advance(); // consume )
            return { type: "CallExpr", name, args };
        }
        return { type: "Identifier", name };
    }
    // ... numbers, parens
}

Evaluating Calls

if (node.type === "CallExpr") {
    const args = node.args.map(a => evaluate(a, env));
    if (node.name === "abs") return Math.abs(args[0]);
    if (node.name === "max") return Math.max(args[0], args[1]);
    if (node.name === "min") return Math.min(args[0], args[1]);
}

Your Task

Add support for abs, max, and min built-in functions. You will need a COMMA token type for argument separation.