[TheCoelacanth]

Depends what you mean by "not declared". Haskell doesn't require you to provide type signatures, so if you don't put a type signature on a function, you can have parameters that aren't explicitly declared (though they still have an inferred static type, so you could use ghci to see what all the parameters are). If you do put any type signature on the function, then all parameters would have to be included.

[lmm]

If I make a typo when using a value parameter in a function definition, can I accidentally introduce an extra value parameter?

If I make a typo when using a type parameter in a function definition, can I accidentally introduce an extra type parameter?

[TheCoelacanth]

> If I make a typo when using a value parameter in a function definition, can I accidentally introduce an extra value parameter?

No.

> If I make a typo when using a type parameter in a function definition, can I accidentally introduce an extra type parameter?

You couldn't introduce a new concrete type. You could introduce a new type variable, but the type signature would still have to typecheck, so it would difficult to come up with a non-contrived example where that would happen.