Common Errors

When something goes wrong, start with the filename and line number in the error message. The actual mistake may be just before that line, such as a missing quote or end.

Missing keywords or brackets

if needs then and end. A function needs end, and a for or while loop needs do and end. A repeat loop ends with until condition instead.

Also check that every (, {, and quote has a matching closing character. Indentation makes missing endings easier to spot:

local fps = 120

if fps >= 60 then
    lh.drawln("Smooth!")
end

Unexpected nil

Errors mentioning arithmetic, concatenation, or indexing a nil value usually mean a value is missing. Check spelling, capitalization, and scope.

local playerName = "iFair"
lh.drawln(playerName) -- Use the same spelling and capitalization.

For an optional value, check before using it:

local name = nil

if name ~= nil then
    lh.drawln("Hello, " .. name)
else
    lh.drawln("No name available.")
end

Calling the wrong value

An error about calling a nil, string, or number means the value before () is not a function. Check the function’s name and whether you accidentally overwrote it.

When passing a callback, use the function itself, as shown in Functions.

Wrong types

"120" is a string; 120 is a number. Use tonumber() for numeric text and check whether it returns nil. Use tostring() before joining a boolean or nil to text.

To inspect a value temporarily:

local value = "120"
lh.drawln("Type: " .. type(value) .. ", value: " .. tostring(value))
-- Output: Type: string, value: 120

Conditions that behave strangely

• Use == to compare values; = assigns them.
• Use ~= for “not equal”, not !=.
• 0 and "" are truthy. Check health > 0 or text ~= "" when that is what you mean.
• condition and first or second chooses second if first is false or nil.

A loop does not finish

Check that its counter changes and its stopping condition can be reached. To run code on later ticks, register a callback instead of waiting in a loop.

Try a small example first, then add the rest back a little at a time. Once these basics make sense, continue to Drawing Your First HUD.