liftMaybe, liftEither, liftExceptT

[jamesdbrock]

Add “validation” functions.

#196

---

Checklist:

• Added the change to the changelog's "Unreleased" section with a link to this PR and your username
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation in the README and/or documentation directory
• Added a test for the contribution (if applicable)

[jamesdbrock]

Any advice @natefaubion ? Is this a good use of Lazy?

[natefaubion]

In general, I consider Lazy to be unnecessary unless you need to rely on memoization of work. Since you only want to defer an argument to potentially evaluate once in a conditional branch, I would use Unit -> a rather than Lazy a. Lazy has overhead in comparison to Unit -> a because it needs to allocate both a mutable reference box and a closure for the work.

[jamesdbrock]

I would use Unit -> a rather than Lazy a

Thx I'll do that.