[Haskell-beginners] Unit numeric type pattern

[Christopher Howard]

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.

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