What is the binary compatibility story of algebra anyway?
I think algebra should follow cats typelevel/cats#1233 WRT binary compat, its similarly fundamental. It can still break binary compat when needed, but such changes should be deliberate and considered, not accidental, and signalled via version numbers.
Should every dependency in a project be tied to a specific algebra release?
Ideally, no, the tying mainly happens when there are compat breaks. At minimum, libs differing on the patch version of algebra they depend upon should never be a problem.
When you "take stock" of what syntax in Spire could be moved to Algebra, it becomes evident that a huge piece of it comes from kernel and not from Algebra.
To the point that there's little point trying to add Algebra syntax without first moving Kernel syntax somewhere that Algebra could reuse it.
Doing that amounts to a migration within cats, adding a syntax package to kernel and adding redirects from cats core.
Group[G].empty syntax used to describe the identity element, instead of the mathematical Group[G].id. But I'm not going to change the underlying cats.kernel typeclass. I'm going to add a short enrichment class to provide Group[G].id and Group[G].isId, and I don't need to break the binary compatibility -- in a sense I define partly my own syntax.
ARep written for GAP version 3. Because it's difficult to port ARep to GAP version 4, several research groups choose to maintain the whole GAP 3 computer algebra system (dating from 1997!) and provide builds for recent Linux distributions.
Algebra is all about compatibility of typeclasses, so it should be as small as possible.
@denisrosset We're in alignment that typeclass compat is important, I dont think Im proposing anything that contradicts that. But that's not all algebra could be about. It could, should IMO, also be useful in its own right.
And every useful typeclass lib in Scala ends up needing syntax enrichment. So if you leave syntax out of either Algebra or Cats Kernel we in effect say, "these libraries must be wrapped within another to be useful".
My position is that we should recognize, based on 10s of examples now, that useful Scala typeclass libs consist of 3 parts: typeclasses themselves, common instances, and syntax to enable infix and postfix operators. Keep the parts together! I see a tendency to treat syntax as a second class citizen, but in practice all the usage I see in the wild assumes syntax is enabled.
I didnt see the relevance of your Group[G].empty example to syntax, since the empty operator isn't provided via syntax but is on the typeclass?
To be clear, when Ive said "syntax" above I specifically refer to enrichment via implicit conversion to enable infix and postfix operators defined on the datatypes of the typeclass. Not "surface syntax" more generally.
Group[G].empty example I meant the following. When aligning algebra to cats, the identity element was renamed the empty element. This makes perfect sense when dealing with monoids such as list or concatenation, but renders group theoretical code difficult to read. For me this is not a big deal, as avoiding typeclass fragmentation is my number #1 goal. By not having the syntax in algebra, I can implement my own infix/postfix operators, as you defined.
algebra should have a syntax on its own and not depend on cats or spire to provide it.
The syntax module would carry a dependency on cats-core (for the reasons described above), and it would only "make sense" if Spire reused it. So the dependency on cats core would extend to Spire.
By not having the syntax in algebra, I can implement my own infix/postfix operators, as you defined.
Re above, I don't think syntax in algebra would or could compromise your ability to enrich Group with an id alias for empty if desired. The kind of syntax Im proposing would enrich data values (only) with typeclass operations
machinist, everything gets inlined)
discipline, the dependency on scalacheck and the laws encoding a lot of structure.