Spurious "Unknown Constructor" errors when misusing `Pair` constructor

[KtorZ]

What Git revision are you using?

What operating system are you using, and which version?

• Linux / Ubuntu
• Linux / Other
• macOS
• Windows

Describe what the problem is?

I noted at least two problems when using the Pair constructor. In both cases, the type-checker fails (rightfully in the second case) with a wrong and confusing error message.

1. When using the constructor as a partial function:

   fuzz.map2(Pair, cardano.credential(), fuzz.int_at_least(1))

   Here, map2 first argument should be fn(a, b) -> Pair(a, b), which in principle Pair satisfies. But instead of providing a relevant error, the compiler fails pointing at an unknown constructor Pair.

2. If we misuse Pair passing only one argument; for example:

   Pair(Credential.Script(permissions_validator_hash, 0))

   The compiler fails again with an unknown constructor error about Pair; confusing.

What should be the expected behavior?

In the first scenario, we the use of Pair as a function should simply be allowed, like it is for all other constructors.
In the second scenario, the compiler should instead raise an incorrect arity error.