discussion: Making the Haskell track more idiomatic

[rbasso]

Making the Haskell track more interesting #192

Making the Haskell track more idiomatic

With #115 we started to review some exercises to make them feel more like Haskell. As a result, we did the following:

• Changed the return type of rna-transcription to a Maybe
• Changed the return type of phone-number to an Either String
• Changed the return type of nucleotide-count to a Maybe

There are many other unidiomatic things that can appear in the track:

• Single letters represented as Strings.
• Using Int when Integer makes more sense.
• Use Integer when any Integral can be used.
• Partial functions instead of returning Maybe.
• Requiring lists when any Foldable is possible.
• ...

This doesn't means that we should change everything that is not idiomatic, because sometimes unidiomatic code can be easier for beginners. But we should not allow it when it it not clear that it is the case.

List of unidiomatic things in the track we could fix

• grains is not a total function. Could return a Maybe. (grains: Change return type to Maybe #197)
• hamming is not defined for unequal lists. Could return a Maybe. (hamming: Change return to Maybe and match json #199)
• etl uses String to represent a single letter. Should use Char. (etl: Change letter representation to Char #198)
• roman-numerals could return a Maybe.
• crypto-square returns a matrix as a String, with spaces representing row breaks and missing elements. (crypto-square: Rewrite it to match x-common or to be more idiomatic. #259)

List of things we could do to promote idiomatic programming

• strain: change tests to enforce lazy processing of the lists. (discussion: Making the Haskell track more idiomatic #194)

Anyone knows of any specific thing that could/should be changed to make this track more idiomatic?

[rbasso]

Should roman-numerals return a Maybe, or Either, if n > 3000 or n < 1?

[petertseng]

I would find Maybe String good.

Note that if truly desired, 3999 could be allowed.

[rbasso]

Note that if truly desired, 3999 could be allowed.

Makes perfect sense. 😄
We should also change 3000 to 3999 in x-common.

[rbasso]

Considering that is issue is open for a while and that we have opened issues to deal with all the agreed changes, I'm closing this PR now, so that we can focus on the more practical issues.

If anyone opposes, I will reopen it immediately.