Cat

Category Theory Abstractions

Inspired by cats library in Scala.

Monadic Syntax

Macro Syntax.monadic rewrites with clauses to nested Functor.map and Monad.flat_map applications. If clause has else expression, it's mapped to ``MonadError.recover`.

Syntax.monadic do
  with a <- Either.right(1),
       _ = IO.puts("x1 = #{a}"),
       b <- Either.left("!"),
       _ = IO.puts("b = #{b}")
    do a + b
  else
    failure ->
      IO.puts(failure)
      Either.right("-")
  end
end

Is rewritten to

MonadError.recover(Monad.flat_map(Either.right(1), fn a ->
  IO.puts("x1 = \#{a}")
  Functor.map(Either.left("!"), fn b ->
    IO.puts("b = \#{b}")
    a + b
  end)
end), fn failure ->
  IO.puts(failure)
  Either.right("-")
end)

Protocols

Delegates

---

• Functor
• Applicative
• Monad
• MonadError

---

• Semigroup
• Monoid.ex

---

• Reducible
• Foldable

Data

• Maybe
• Either