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Invalid Lua argument

lua
A value passed to a pandoc.* constructor or function has the wrong type.

Q-11-3 — Invalid Lua argument

A value passed to a pandoc.* constructor or function has the wrong type.

What this means

The pandoc.* constructors build AST elements, and each one expects particular argument types. When an argument does not match, Quarto stops the filter and reports what was expected and what arrived:

Q-11-3: pandoc.Meta: expected table (Meta), got string

Lua is permissive about types, so this check is deliberately not. A constructor that silently coerced its argument would build a malformed element, and the failure would surface much later — during writing, far from the filter line that caused it.

Note that Lua’s truthiness rules do not apply. pandoc.MetaBool('x') is an error, not true, matching pandoc’s own behavior.

Why this happens

  • Passing a Lua string where a list of inlines is expected. Many constructors take inline content, not text: pandoc.Emph("hi") works because strings are accepted in inline positions, but structural arguments like a Meta table are not coerced.
  • Argument order. pandoc.Pandoc(blocks, meta) takes blocks first; swapping them produces a type error on the second argument.
  • A nil that was meant to be a value, typically from a field lookup that missed — elem.attributes.width when the attribute is absent.
  • A plain Lua table where a constructed element is expected. A table with the right-looking keys is not an AST element; build it with the constructor.

How to fix

Read the expected type from the message and construct that type explicitly.

-- error: expected table (Meta), got string
local m = pandoc.Meta('title')

-- correct
local m = pandoc.Meta({ title = pandoc.MetaString('title') })

When a value may be absent, guard it rather than passing it through:

local width = elem.attributes.width
if width then
  -- use width
end

If you are unsure what a constructor expects, pandoc.utils.type(value) reports the pandoc type of an existing value, which is usually faster than reading it off the error.