On Thu, 3 Jun 2021, Travis Cardwell wrote:
On Thu, Jun 3, 2021 at 2:57 PM Henning Thielemann wrote:
That is, your class is intended for text representation for program users (instead of programmers)?
Yes, that is correct. While Show instances should produce valid Haskell code and Read instances should parse that code to create the original value, forming an isomorphism, the Render and Parse type classes can be used by the developer to define instances as required for each particular application. The Render and Parse type classes in Data.TTC have no instances, allowing developers to write their own instances for Int for example, but some default instances can optionally be imported from Data.TTC.Instances when they are appropriate.
Are these instances orphan?
The common way to get around the one-instance-per-type limitation is to use newtypes. I generally do not use this strategy with TTC to provide different ways to format text, however.
Is it feasible to have a newtype for any of "%3d", "%03d", "%05d" ...?