Common Runtime Errors Reference

Error snippet	Cause	How to fix
attempt to perform arithmetic on a	Tried arithmetic (+, -, *, /) on a non-number	Validate operands are numbers before arithmetic
attempt to compare	Tried comparison (>, <, >=, <=) on invalid values	Validate both operands are comparable before comparison
attempt to concatenate a	Tried concatenating a non-string with ..	Ensure both sides are strings before concatenation
attempt to call a	Tried to call a value that is not a function	Ensure the value is a function before calling
attempt to index a	Tried to index (subscript) a non-table value	Ensure the variable is a table before indexing
attempt to yield across a C-call boundary	Tried to yield in a context that cannot yield	When using require, ensure the required module returns without calling yielding functions (marked with exclamation in this handbook). Also avoid using yielding functions in callbacks with C bridges.
invalid order function for sorting	Invalid sort comparator; comparison logic is inconsistent	Use a strict order function; it must not be simultaneously a>b and a<b for any pair
bad argument #1 to 'xxx' (number expected, got nil)	Argument #1 to function 'xxx' is invalid; number expected but got nil	Pass a valid argument of the expected type
bad argument #2 to 'xxx' (number has no integer representation)	Argument #2 cannot be represented as an integer	Pass a valid argument
bad argument #3 to 'xxx'	Argument #3 is invalid	Pass a valid argument

• Workaround for "attempt to yield across a C-call boundary" when using require:
  • 1. Add return function() to the first line of the required module
  • 2. Add end at the last line of the module
  • 3. Add an extra pair of parentheses when requiring: change require('A') to require('A')()