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typelevel / algebra

Experimental project to lay out basic algebra type classes
https://typelevel.org/algebra/
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Add Show typeclass #106

Closed rklaehn closed 8 years ago

rklaehn commented 8 years ago

This might be a bit controversial, since Show is not really "algebraic". But I think that algebra-core has the potential to become something like the predef for people working with typeclasses.

I would like to have a typeclass-based alternative to everything in java.lang.Object in algebra-core. Eq already exists. There is issue #38 for adding a simple hashing typeclass. So that leaves Show.

There is a Show in cats: https://github.com/non/cats/blob/master/core/src/main/scala/cats/Show.scala . Maybe just move that one level up?

johnynek commented 8 years ago

Eq and Hash are lawful and useful to algebraic code. I wish scala had a Show typeclass, but I'd tend say we should not have it here. You have a barrier against the slippery slope: adding only typeclasses implied by Object, but still I'm weakly opposed.

Next, other than style, I'm not sure what is that bad about .toString. I mean, I would not design a new language with .toString on everything, but given that Java and scala already did that, I'm not sure the win of having Show other style purity.

rklaehn commented 8 years ago

I see your point of view.

About why having Show: often implementing toString requires access to typeclass instances. So you have to capture the typeclass instances into your data structures in order to implement toString, which is inefficient, and also drives you to a more OO design.

tixxit commented 8 years ago

Yeah - a good point. I don't think toString is too bad, but an example in Spire is that we often have to use this really nasty hack to work with generic values when we don't have a type class available to help us. This shows up more when implementing equals and many of the ScalaNumber methods :\

That said, I'd rather not have Show here as well.