Baccata

Explaining Miles's Magic

Miles Sabin recently opened a pull request fixing the infamous SI-2712. First off, this is remarkable and, if merged, will make everyone's life enormously easier. This is a bug that a lot of people hit often without even realizing it, and they just assume that either they did something wrong or the compiler is broken in some weird way. It is especially common for users of scalaz or cats.

But that's not what I wanted to write about. What I want to write about is the exact semantics of Miles's fix, because it does impose some very specific assumptions about the way that type constructors work, and understanding those assumptions is the key to getting the most of it his fix.

For starters, here is the sort of thing that SI-2712 affects:

def foo[F[_], A](fa: F[A]): String = fa.toString

Baccata

// Look up ammonite if you're wondering what this syntax is
import $ivy.`org.typelevel::cats-core:1.0.0-MF`

import cats._
import cats.syntax.functor._
import cats.syntax.traverse._

sealed trait Nat[+A]
case object Zero extends Nat[Nothing]
case class Succ[A](a : A) extends Nat[A]

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package presentation

import matryoshka.data.Fix

import scalaz.Functor

object Presentation extends App {

  // 1 : abstract recursion away

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# See https://debian-administration.org/article/317/An_introduction_to_bash_completion_part_2
__mill()
{
  local cur prev opts
  COMPREPLY=()
  cur="${COMP_WORDS[COMP_CWORD]}"
  prev="${COMP_WORDS[COMP_CWORD-1]}"
  opts="$(echo $(mill resolve __ 2>/dev/null ) | sed 's/ / /g')"
  COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
  return 0

Baccata

import $ivy.`org.typelevel::cats-core:1.0.1`
import cats.data.NonEmptyList

case class ABC(a : Int, b : Long, c : String)

case class NelWrapper(nel: NonEmptyList[Int])

val w = NelWrapper(NonEmptyList.of(1,2,3,4))

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package ammonite
package $file
import _root_.ammonite.interp.InterpBridge.{
  value => interp
}
import _root_.ammonite.interp.InterpBridge.value.{
  exit
}
import _root_.ammonite.main.Router.{
  doc,

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/**
  * Function that allows values to be discarded in a visible way
  *
  * Thanks https://github.com/tabdulradi for the Trick
  */
object ValueDiscard {

  /**

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abstract class FoldableFromTraverse[F[_]] extends Traverse[F] {

  override def foldMap[A, B: Monoid](fa: F[A])(f: A => B): B =
    traverse[Const[B, ?], A, B](fa)(a => Const(f(a))).getConst

  private def andThenMonoid[A]: Monoid[A => A] = new Monoid[A => A] {
    def combine(f: A => A, g: A => A) = f andThen g
    def empty: A => A                 = (a: A) => a
  }

Baccata

package teikametrics

import cats.effect.{Sync, Timer}

import scala.concurrent.duration.FiniteDuration
import scala.concurrent.blocking
import cats.syntax.all._

object JavaFuture {
  // Alias for more friendly imports

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#!/usr/bin/env bash

HOST="???" # address of the vpn 
LASTPASS_ENTRY="???" # entry under which the password is saved in last pass

USERNAME=$(lpass show --sync=auto --username $LASTPASS_ENTRY)
PASSWORD=$(lpass show --sync=auto --password $LASTPASS_ENTRY)
# escaping the special chars in the password to allow sed-ing it
ESC_PWD=$(echo $PASSWORD | sed -e 's/[]\/$*.^[]/\\&/g')