gastownhall/beads · error

division by zero

Error message

division by zero

What it means

parseMulDiv performs '/' only after checking the right operand is non-zero; a zero divisor raises this explicit error instead of returning IEEE +Inf. The library fails fast so users get a clear message rather than silently infinite/NaN results.

Source

Thrown at internal/formula/range.go:283

	}

	for {
		switch p.current().typ {
		case tokMul:
			p.advance()
			right, err := p.parsePow()
			if err != nil {
				return 0, err
			}
			left *= right
		case tokDiv:
			p.advance()
			right, err := p.parsePow()
			if err != nil {
				return 0, err
			}
			if right == 0 {
				return 0, fmt.Errorf("division by zero")
			}
			left /= right
		default:
			return left, nil
		}
	}
}

// parsePow handles ^ (power, highest binary precedence, right-associative)
func (p *exprParser) parsePow() (float64, error) {
	base, err := p.parseUnary()
	if err != nil {
		return 0, err
	}

	if p.current().typ == tokPow {
		p.advance()
		exp, err := p.parsePow() // Right-associative

View on GitHub (pinned to 71377f2769)

Solutions

1. Guard the divisor: use a non-zero constant or check the substituted variable value before evaluation
2. Rewrite as multiplication by a safe value or clamp the divisor (e.g. 'x/max(y,1)')
3. Log/inspect the variable values feeding the expression

Example fix

// before
range 1..count/0 { ... }
// after
range 1..count/workers { ... } // ensure workers != 0

// before evaluating, ensure no variable that appears as a divisor is zero
for name, v := range vars {
    if v == 0 { return fmt.Errorf("variable %s is zero; used as divisor", name) }
}

val, err := EvaluateExpr(expr, vars)
if err != nil && strings.Contains(err.Error(), "division by zero") {
    // substitute safe defaults for zero variables and retry
}

When it happens

Trigger: EvaluateExpr with a division whose right side evaluates to 0, e.g. '10/0' or '8/(2-2)' in a range endpoint like 'range 1..10/0'.

Common situations: Variable placeholders substituted with 0 (empty config values), computed denominators that hit zero at runtime, off-by-one arithmetic like 'n-n'.

Related errors

• unexpected token after expression
• expected closing parenthesis
• unexpected token in expression
• parsing formula: %w
• resolving formula: %w

AI-assisted analysis of gastownhall/beads@71377f2769 (2026-08-30). Data as JSON: /api/errors/fed6f948e8314cce. Report an issue: GitHub.