Is RefType a Prism in disguise?

The main operations of RefType are unwrap and refine if we ignore the unsafe operations and the macros. unwrap has type F[T, P] => T and refine has type T => Either[String, F[T, P]]. If we set type S = F[T, P] and ignore the error message in Either, we get this pair of functions:

S => T
T => Option[S]

This looks similar to a Prism. I’d like to study lens libraries and Prism in more detail. Maybe we can borrow laws and concepts from the lens world and streamline RefType.

[julien-truffaut]

You’re completely right. Forget what I said, we should be able to create a Prism for all refined type

[fthomas]

Aha. But refined’s Xml predicate does not change a String to a scala.xml.Elem. It merely tags the source String without modifying it:

scala> "<div></div>": String Refined Xml
res0: eu.timepit.refined.api.Refined[String,eu.timepit.refined.string.Xml] = <div></div>

scala> res0.value
res1: String = <div></div>

scala.xml.XML.loadString is used in the Validate[String, Xml] instance only for checking that the source string is valid XML.