Circular newtype wrapper: Enables all enum methods

[Hyalunar]

I wrote this code sometime and figured I might contribute it back after polishing it up.

Creates a newtype called Circular and implements the Enum typeclass for it.
All operations using the Enum instance are now circular, none call error (something that often annoyed me), but some may produce infinite lists, when given the right arguments.

I also added some tests, but I'm not very versed with unit testing.
Feel free to suggest more test cases, I could also add QuickCheck tests.

If desired, I could also imagine adding more methods like already present (csucc and cpred), which just wrap to Circular internally.

[memowe]

Thank you very much for your contribution, I like your work! 🚀 I just checked it out locally and start reading it in detail, let's work together on this.

Maybe let's discuss some things first:

I could also add QuickCheck tests.

What property tests do you suggest?

I could also imagine adding more methods like already present (csucc and cpred), which just wrap to Circular internally.

As there's no runtime penalty for using newtypes, I think it makes sense to go all in use it internally for csucc/cpred. What other functions to you suggest?

[Hyalunar]

What property tests do you suggest?

Sadly, I don't have Ideas for meaningful property based testing, since the Enum must be defined in the source code which would not allow for much randomness.
Sorry if this was confusing, I wanted to advertise my ability to add QuickCheck tests if you wanted some.

As there's no runtime penalty for using newtypes, I think it makes sense to go all in use it internally for csucc/cpred. What other functions to you suggest?

I thought about the other enum functions which would then do the wrapping for you, namely:

• toEnum: using mod on maxBound
• fromEnum, this one is not very useful, but could be included for completeness
• enumFrom
• enumFromThen
• enumFromTo
• enumFromThenTo

For consistency with the current API, these could all be prefixed with c.

[memowe]

Actually, I don't know if we should derive Bounded here as the whole point of this newtype is to go beyond boundaries.

[memowe]

I tried to address this in 2ca189e

[memowe]

When/If this is ready to join,

• move GHC extensions to cabal file

[Hyalunar]

I have moved the Language Extensions to circular-enum.cabal. As a Bonus: It seems like this is compatible with MicroHS.

[memowe]

I'm working on it. :) Stay tuned. :)