Alternative version of Host.fromString that returns error message?

[george-wilson-rea]

I recently had a problem where Host.fromString failed due to an underscore character (which seems reasonable). Could you provide an alternate version, eg. Host.fromStringEither which explains why host parsing failed?

[mpilquist]

We could follow the precedent from scodec-bits and add def fromStringDescriptive(s: String): Either[String, Host]. We'd need to do that for a bunch of types though, not just Host. We'd also need to ensure the error messages are useful and not just stuff like ""foo_bar" is not a valid ip address, hostname, or IDN"

[george-wilson-rea]

I had a go at implementing this and found it difficult. Since a host is one of three things, at least two of them will fail, so if all three fail (eg. something that's a hostname but an invalid one) then it's hard to know which one it was supposed to be. Something more specific would fix this, but then there'd be a proliferation of methods HostName.fromStringDescriptive Ipv4Address.fromStringDescriptive etc.