Re: [core libraries] Re: Tightening up on inferred type signatures

On 23/04/2014 20:04, dm-list-haskell-libraries@scs.stanford.edu wrote:

Edward Kmett writes:

...

You can wind up in perfectly legitimate situations where the name for the type you are working with isn't in scope, but where you can write a combinator that would infer to have that type. I'd hate to lose that.

It is admittedly of marginal utility at first glance, but there are some tricks that actually need it, and it can also arise if a type synonym expands to a type that isn't exported or brought into scope, so trying to push this line of reasoning too far I is possibly not too productive.

Good point. In particular, it's not weird at all want to export type synonyms on their own, particularly where ghost type parameters are used to select between only a few cases. Consider something like this (inspired by postgresql-orm):

Is there an abstraction being protected by only exporting the type synonym in cases like this? Cheers, Ganesh