purescript-deprecated / purescript-monoid Goto Github PK

I need Zero but not Semigroup for one of my projects: https://github.com/michaelficarra/purescript-filterable/blob/577b4ef73697c1998219193b728a8b2a724a44a0/src/Data/Filterable.purs

PR incoming

This is more general and especially useful with Star.

newtype Endo c a = Endo (c a a)

instance Semigroupoid c => Semigroup (Endo c a) where
  append (Endo f) (Endo g) = Endo (f <<< g)

instance Category c => Monoid (Endo c a) where
  mempty = Endo id

Is it worth including something like newtype Transformation = Transformation (t -> t) with a Monoid over composition and mempty = id?

This would make it safe to foldMap into an Endofunctor. @natefaubion I recall you making something like this on Slack at some point.

edit: now toposorted

• purescript-tuples
• purescript-foldable-traversable
• purescript-foreign
• purescript-quickcheck
• purescript-arb-instances
• purescript-maps
• purescript-sets
• purescript-profunctor
• purescript-arrows
• purescript-const
• purescript-bifunctors
• purescript-identity
• purescript-distributive
• purescript-lens
• purescript-transformers
• purescript-lazy
• purescript-channels
• purescript-coproducts
• purescript-generics
• purescript-drawing
• purescript-unfoldable
• purescript-enums
• purescript-datetime
• purescript-lists
• purescript-inject
• purescript-free
• purescript-angular
• purescript-graphs
• purescript-jquery
• purescript-handlebars
• purescript-machines
• purescript-strongcheck
• purescript-argonaut
• purescript-base
• purescript-mongodbf
• purescript-node-fs
• purescript-oo-ffi
• purescript-parsing
• purescript-pattern-arrows
• purescript-sammy
• purescript-string-parsers
• purescript-yaml
• purescript-yargs

Sounds un-PureScript-y. @garyb suggested leaving Plus as is and picking something here when modules get renamed.

Should we release as v0.2.0 after this, or just v0.1.6? The latter has the advantage of us not having to rerelease that massive list of things I mentioned in the issue about Num, but as this will require a new version of the compiler it sort of is a breaking change.

Should there be Unfoldable instances for the Monoid newtypes?

It might be useful to add a CommutativeMonoid superclass of Monoid. This came up in the discussion here: purescript/purescript-prelude#87. It would not introduce any new operations, but require <> to be a commutative operation.

On the other hand, I currently cannot think of any function that would make use of the CommutativeMonoid constraint 😄

Note that another option would be to add CommutativeSemigroup and let CommutativeMonoid be derived from CommutativeSemigroup and Monoid.

Do you think this library should include a function mconcat :: Monoid a => [a] -> a, like Haskell's? I'd be happy to put a pull request together if so.

I only see 3.0.0 on Pursuit, and links from other modules are currently broken -- for examplefrom https://pursuit.purescript.org/packages/purescript-foldable-traversable/3.4.0/docs/Data.Semigroup.Foldable#v:foldMap1