Claude Sonnet 5 vs Claude Haiku 4.5

A hard prompt: “Evaluate an arithmetic expression, no eval”, in full.

• Claude Sonnet 5

  Passed: All 15 tests passed.

  ```javascript
  function evaluate(expression) {
    // ---- Tokenizer ----
    const tokens = [];
    let i = 0;
    const s = expression;
    while (i < s.length) {
      const c = s[i];
      if (c === ' ' || c === '\t' || c === '\n' || c === '\r') {
        i++;
        continue;
      }
      if ('+-*/^()'.includes(c)) {
        tokens.push(c);
        i++;
        continue;
      }
      if ((c >= '0' && c <= '9') || c === '.') {
        let start = i;
        let seenDot = false;
        let seenDigit = false;
        while (i < s.length && ((s[i] >= '0' && s[i] <= '9') || s[i] === '.')) {
          if (s[i] === '.') {
            if (seenDot) break;
            seenDot = true;
          } else {
            seenDigit = true;
          }
          i++;
        }
        const raw = s.slice(start, i);
        if (!seenDigit || !/^\d*\.?\d*$/.test(raw)) {
          throw new Error(`Invalid number: "${raw}"`);
        }
        tokens.push({ type: 'num', value: parseFloat(raw) });
        continue;
      }
      throw new Error(`Unexpected character "${c}" at position ${i}`);
    }
  
    // ---- Parser ----
    let pos = 0;
  
    function peek() {
      return tokens[pos];
    }
  
    function next() {
      return tokens[pos++];
    }
  
    function expect(tok) {
      const t = next();
      if (t !== tok) {
        throw new Error(`Expected "${tok}" but got "${t === undefined ? 'end of input' : (typeof t === 'object' ? t.value : t)}"`);
      }
    }
  
    function parseExpr() {
      let value = parseTerm();
      while (peek() === '+' || peek() === '-') {
        const op = next();
        const rhs = parseTerm();
        value = op === '+' ? value + rhs : value - rhs;
      }
      return value;
    }
  
    function parseTerm() {
      let value = parseUnary();
      while (peek() === '*' || peek() === '/') {
        const op = next();
        const rhs = parseUnary();
        if (op === '*') {
          value = value * rhs;
        } else {
          value = value / rhs;
        }
      }
      return value;
    }
  
    function parseUnary() {
      if (peek() === '-') {
        next();
        return -parseUnary();
      }
      if (peek() === '+') {
        next();
        return parseUnary();
      }
      return parsePower();
    }
  
    function parsePower() {
      const base = parseAtom();
      if (peek() === '^') {
        next();
        const exponent = parseUnary(); // right-associative, allows unary minus
        return Math.pow(base, exponent);
      }
      return base;
    }
  
    function parseAtom() {
      const t = peek();
      if (t === undefined) {
        throw new Error('Unexpected end of input');
      }
      if (t === '(') {
        next();
        const value = parseExpr();
        expect(')');
        return value;
      }
      if (typeof t === 'object' && t.type === 'num') {
        next();
        return t.value;
      }
      throw new Error(`Unexpected token "${typeof t === 'object' ? t.value : t}"`);
    }
  
    if (tokens.length === 0) {
      throw new Error('Empty expression');
    }
  
    const result = parseExpr();
  
    if (pos !== tokens.length) {
      const remaining = tokens[pos];
      throw new Error(`Unexpected token "${typeof remaining === 'object' ? remaining.value : remaining}" after expression`);
    }
  
    return result;
  }
  ```

  760 tokens in, 2,110 out (834 of them reasoning) · 16.9 s · $0.0226 · 1 message on Pro · answered by anthropic/claude-sonnet-5 via Claude Platform on AWS · September 27, 2026

• Claude Haiku 4.5

  Failed: 14 of 15 tests passed. First failure: evaluate("-2 ^ 2"): Expected values to be strictly deep-equal:

  ```javascript
  function evaluate(expression) {
    const tokens = tokenize(expression);
    const parser = new Parser(tokens);
    const result = parser.parseExpression();
    
    if (parser.pos !== tokens.length) {
      throw new Error("Unexpected tokens after expression");
    }
    
    return result;
  }
  
  function tokenize(expression) {
    const tokens = [];
    let i = 0;
    
    while (i < expression.length) {
      const ch = expression[i];
      
      if (/\s/.test(ch)) {
        i++;
        continue;
      }
      
      if (/\d/.test(ch)) {
        let num = '';
        while (i < expression.length && /[\d.]/.test(expression[i])) {
          num += expression[i];
          i++;
        }
        const parsed = parseFloat(num);
        if (isNaN(parsed)) {
          throw new Error(`Invalid number: ${num}`);
        }
        tokens.push({ type: 'NUMBER', value: parsed });
        continue;
      }
      
      if ('+-*/^()'.includes(ch)) {
        tokens.push({ type: ch, value: ch });
        i++;
        continue;
      }
      
      throw new Error(`Unexpected character: ${ch}`);
    }
    
    return tokens;
  }
  
  class Parser {
    constructor(tokens) {
      this.tokens = tokens;
      this.pos = 0;
    }
    
    peek() {
      return this.tokens[this.pos];
    }
    
    consume() {
      return this.tokens[this.pos++];
    }
    
    parseExpression() {
      return this.parseAddSub();
    }
    
    parseAddSub() {
      let left = this.parseMulDiv();
      
      while (this.peek() && (this.peek().type === '+' || this.peek().type === '-')) {
        const op = this.consume().type;
        const right = this.parseMulDiv();
        left = op === '+' ? left + right : left - right;
      }
      
      return left;
    }
    
    parseMulDiv() {
      let left = this.parsePower();
      
      while (this.peek() && (this.peek().type === '*' || this.peek().type === '/')) {
        const op = this.consume().type;
        const right = this.parsePower();
        left = op === '*' ? left * right : left / right;
      }
      
      return left;
    }
    
    parsePower() {
      let left = this.parseUnary();
      
      if (this.peek() && this.peek().type === '^') {
        this.consume();
        const right = this.parsePower();
        left = Math.pow(left, right);
      }
      
      return left;
    }
    
    parseUnary() {
      if (this.peek() && this.peek().type === '-') {
        this.consume();
        return -this.parseUnary();
      }
      
      if (this.peek() && this.peek().type === '+') {
        this.consume();
        return this.parseUnary();
      }
      
      return this.parsePrimary();
    }
    
    parsePrimary() {
      const token = this.peek();
      
      if (!token) {
        throw new Error("Unexpected end of expression");
      }
      
      if (token.type === 'NUMBER') {
        this.consume();
        return token.value;
      }
      
      if (token.type === '(') {
        this.consume();
        const result = this.parseExpression();
        
        if (!this.peek() || this.peek().type !== ')') {
          throw new Error("Missing closing parenthesis");
        }
        
        this.consume();
        return result;
      }
      
      throw new Error(`Unexpected token: ${token.value}`);
    }
  }
  ```

  599 tokens in, 1,007 out · 7.6 s · $0.0056 · 1 message on Pro · answered by anthropic/claude-haiku-4.5 via Amazon Bedrock · September 27, 2026