Added Rational Numbers exercise

[tofische]

Added a new Haskell practice exercise Rational Numbers based on the available problem specification.

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[MatthijsBlom]

I don't think reduce should be exported. Going by the instructions there shouldn't be a need for that either:

Your implementation of rational numbers should always be reduced to lowest terms.

I understand this to mean that it should be impossible for a user of this module to construct unreduced fractions.

To still be able to test proper reduction, we could require export of projections numerator and denominator.

[ErikSchierboom]

@MatthijsBlom Ping me when you've approved!

[MatthijsBlom]

We now have rational :: (a, a) -> Rational a, but this allows creating fractions with 0 as denominator. Seemingly, having rational :: (a, a) -> Maybe (Rational a) would be more idiomatic. However, then div would still allow us to commit division by zero, so I think we might as well keep the present rational :: (a, a) -> Rational a.

[tofische]

I don't think reduce should be exported. Going by the instructions there shouldn't be a need for that either:

Your implementation of rational numbers should always be reduced to lowest terms.

I understand this to mean that it should be impossible for a user of this module to construct unreduced fractions.

To still be able to test proper reduction, we could require export of projections numerator and denominator.

You are correct, I'll update the exercise.

[ErikSchierboom]

@MatthijsBlom could you review again?

[tofische]

I'm now a little bit confused - shall I do something in order to enable this PR to be merged?

[MatthijsBlom]

Sorry, I haven't been able to find the energy to review properly again.

[tofische]

Sorry, I haven't been able to find the energy to review properly again.

No problem, I was just unsure because one check (although not required) failed.

[ErikSchierboom]

@MatthijsBlom if you haven't found the time in the next couple of days, I'll look into it

[ErikSchierboom]

LGTM! @MatthijsBlom If you find time and find things to improve, we can do that as a follow-up PR.