Function applySumPredicate

optimizer/sum_range.go:113–152

applySumPredicate tries to compute the result of sum(m..n, predicate) at compile time. Returns (result, true) if optimization is possible, (0, false) otherwise. Supported predicates: - # (identity): result = sum - # * k (multiply by constant): result = k * sum - k * # (multiply by constant): result

(sum, count int, predicateArg Node)

//   - k + # (add constant): result = sum + count * k
//   - # - k (subtract constant): result = sum - count * k
func applySumPredicate(sum, count int, predicateArg Node) (int, bool) {
	predicate, ok := predicateArg.(*PredicateNode)
	if !ok {
		return 0, false
	}

	// Case 1: # (identity) - just return the sum
	if pointer, ok := predicate.Node.(*PointerNode); ok && pointer.Name == "" {
		return sum, true
	}

	// Case 2: Binary operations with pointer and constant
	binary, ok := predicate.Node.(*BinaryNode)
	if !ok {
		return 0, false
	}

	pointer, constant, pointerOnLeft := extractPointerAndConstantWithPosition(binary)
	if pointer == nil || constant == nil {
		return 0, false
	}

	switch binary.Operator {
	case "*":
		// # * k or k * # => k * sum
		return constant.Value * sum, true
	case "+":
		// # + k or k + # => sum + count * k
		return sum + count*constant.Value, true
	case "-":
		if pointerOnLeft {
			// # - k => sum - count * k
			return sum - count*constant.Value, true
		}
		// k - # => count * k - sum
		return count*constant.Value - sum, true
	}

	return 0, false
}

// extractPointerAndConstantWithPosition extracts pointer (#) and integer constant from a binary node.
// Returns (pointer, constant, pointerOnLeft) or (nil, nil, false) if not matching the expected pattern.