hobwekiva

/////////////////////////////////////////////////////////////
// A direct translation of this tweet
// https://twitter.com/tiarkrompf/status/963314799521222656
// to pure functional style.
/////////////////////////////////////////////////////////////

import cats.{Functor, Applicative, Monad}
import cats.effect.{ IO }
import cats.instances.list._
import cats.syntax.all._

aaronlevin

package cats

import cats.data.{StateT, WriterT}
import cats.implicits._

/**
 * TypeLevel is working on some alternative encodings of the Monad Transformer
 * Library (MTL). The existing solution in cats was broken for a few reasons.
 * One annoying issue made it imposisible to use for-comprehension with more
 * than one Monad$FOO constraint owing to implicit resolution ambiguities.

paulp

// These lines go in ~/.sbt/0.13/global.sbt
watchSources ++= (
     (baseDirectory.value * "*.sbt").get
  ++ (baseDirectory.value / "project" * "*.scala").get
  ++ (baseDirectory.value / "project" * "*.sbt").get
)

addCommandAlias("rtu", "; reload ; test:update")
addCommandAlias("rtc", "; reload ; test:compile")
addCommandAlias("ru", "; reload ; update")

gkossakowski

Scala's "type T in class C as seen from a prefix type S" with examples

Introduction

Recently, I found myself in need to precisely understand Scala's core typechecking rules. I was particulary interested in understanding rules responsible for typechecking signatures of members defined in classes (and all types derived from them). Scala Language Specification (SLS) contains definition of the rules but lacks any examples. The definition of the rules uses mutual recursion and nested switch-like constructs that make it hard to follow. I've written down examples together with explanation how specific set of rules (grouped thematically) is applied. These notes helped me gain confidence that I fully understand Scala's core typechecking algorithm.

As Seen From

Let's quote the Scala spec for As Seen From (ASF) rules numbered for an easier reference:

rodolfo42

package transactions

import com.twitter.finagle.exp.mysql.{Client, OK, Result}

class Db(mysqlClient: Client) {

    val insertOrder     = "INSERT INTO orders (ref) VALUES(?)"
    val insertOrderItem = "INSERT INTO order_items (order_id, item_id) VALUES(?, ?)"

    def persistOrderWithItems[T](order: Order)(whenDone: (OK, Seq[Result]) => T): Future[T] = {