The required context on pattern synonyms isn't just useful, it's
necessary. Since arbitrary computation can happen in both the pattern
matching and construction we need the context.
Take Richard's example, without the context on Positive we would infer the
wrong type for any use of the Positive
You're right that these features sit in a similar space. The difference is
that, with a pattern synonym, the required context might be useful. This is
because pattern synonyms can perform computation (via view patterns), and this
computation might plausibly require some class constraint. An
