fthomas

trait InvariantLaws[F[_]] {
  implicit def F: Invariant[F]

  ...
}

object InvariantLaws {
  apply[F[_]](implicit ev: Invariant[F]): InvariantLaws[F] =
    new InvariantLaws { def F = ev }
}

fthomas

import Control.Arrow

type IsEq a = (a, a)

splitInterchange :: (Arrow f) => f a1 a2 -> f a2 a3 -> f b1 b2 -> f b2 b3
                              -> IsEq (f (a1, b1) (a3, b3)) 
splitInterchange f1 f2 g1 g2 = (lhs, rhs)
  where
    lhs = (f1 >>> f2) *** (g1 >>> g2)
    rhs = (f1 *** g1) >>> (f2 *** g2)

fthomas

case class A(i: Int)

object A {
  implicit class ASyntax(val self: A) extends AnyVal {
    def twice: Int = self.i * 2
  }

  implicit def toASyntax2(a: A): ASyntax2 =
    new ASyntax2(a)
}

fthomas

trait Semigroup[A] {
  def op(a1: A, a2: A): A // op is associative
}

trait Monoid[A] extends Semigroup[A] {
  def id: A // id is the identity of op: op(a, id) == op(id, a) == a
}

trait SemigroupZero[A] extends Semigroup[A] {
  def zero: A // zero is the absorbing element of op: op(a, zero) == op(zero, a) == zero

fthomas

isSorted : Ord a => List a -> Bool
isSorted []  = True
isSorted [x] = True
isSorted (x :: t @ (y :: ys)) = x <= y && isSorted t

minElem : Ord a => (l : List a) -> { auto p : isSorted l = True } -> Maybe a
minElem l = head' l

prove : Ord a => (l : List a) -> Maybe (isSorted l = True)
prove []  = Just $ Refl

fthomas

object AsyncCallbackInstances {
  implicit val asyncCallbackAsync: Async[AsyncCallback] = new Async[AsyncCallback] {
    override def async[A](k: (Either[Throwable, A] => Unit) => Unit): AsyncCallback[A] =
      AsyncCallback((cb: Try[A] => Callback) => Callback(k(r => cb(r.toTry).runNow())))

    override def asyncF[A](k: (Either[Throwable, A] => Unit) => AsyncCallback[Unit]): AsyncCallback[A] =
      AsyncCallback((cb: Try[A] => Callback) => k(r => cb(r.toTry).runNow()).toCallback)

    override def suspend[A](thunk: => AsyncCallback[A]): AsyncCallback[A] =
      AsyncCallback.byName(thunk)

fthomas

https://www.umsu.de/trees/#((a%E2%86%92c)%E2%88%A7(b%E2%86%92d))%E2%86%92((a%E2%88%A7b)%E2%86%92(c%E2%88%A7d))

---

A -> C
B -> D
A & B
---
C & D

fthomas

package fix

import scalafix.v1._
import scala.meta._

class v1_2_0 extends SemanticRule("v1_2_0") {
  override def fix(implicit doc: SemanticDocument): Patch = {
    doc.tree.collect {
      case t @ Term.Select(Term.Select(Term.Select(Term.Name("_root_"), Term.Name("io")), Term.Name("chrisdavenport")), Term.Name("log4cats")) =>
        Patch.replaceTree(t, "_root_.org.typelevel.log4cats")