Coercion and datatype contexts

This week we’ve written a couple articles covering some one-off topics that needed to be addressed:

• How do you use the coerce function, and what types are coercible? TheThe discussion of coercion ties in very neatly to our previous page on deriving via; as it turns out, the two features are intimately related. documentation for the Data.Coerce module is very sparse, and it might lead you to thing that coercion isn’t very useful – But there are so many things to coerce! This is reflected in the many arrows we have drawn in our diagrams.

• Why can’t you put typeclass constraints on datatype definitions? As is often the case, you can if you enable a language extension. But it’s not a great idea, and the important lesson here is about understanding why.