[Haskell-beginners] Unit numeric type pattern

What is a "unit numeric type pattern", as in the error: "Only unit numeric type pattern is valid". I can cause this error by mixing numbers into type definitions. And, therefore, I know how to avoid this error. But the error indicates that there /is/ such a thing as "valid" "unit numeric type pattern", and consequently I am quite curious as to what a such a thing is and what it would look like in code. -- frigidcode.com theologia.indicium.us