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    public void CreateExpression()
    {
        Type argType = typeof (MyClass);
        string propertyName = "Name";

        ParameterExpression paramExpression = Expression.Parameter(argType, "item");

        //Create "item.Name" and "item.GetType()" expressions
        var propertyAccessExpression = Expression.Property(paramExpression, propertyName); 
        var getTypeExpression = Expression.Call(paramExpression, "GetType", Type.EmptyTypes);

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The problem

These programs are safe to refactor:

object p1 {
  val x = 1 + 123
  val y = 1 + 123
}

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{
  "envelope_id": "f34c6197-a7ef-45ed-acad-4d5a3147ec86",
  "payload": {
    "token": "Pct6Sm6JynybrFXkjEiH7hhX",
    "team_id": "T02NDBHSWSG",
    "api_app_id": "A03BLN935DK",
    "event": {
      "type": "message",
      "subtype": "message_changed",
      "message": {

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{
  "envelope_id": "012327ef-4c84-41e3-a952-09af25782c17",
  "payload": {
    "token": "Pct6Sm6JynybrFXkjEiH7hhX",
    "team_id": "T02NDBHSWSG",
    "api_app_id": "A03BLN935DK",
    "event": {
      "client_msg_id": "0837851c-2d34-4d4d-804c-7aed753c3421",
      "type": "message",
      "text": "Hello world",

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>>>>0: https://hangzhou.testnet.tezos.serokell.team/version
>>>>1: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/protocols
>>>>2: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/context/contracts/tz1ZSedNyGuqibEYCPbuMS3yEhhLHfZEuLtA/counter
>>>>3: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/context/contracts/tz1ZSedNyGuqibEYCPbuMS3yEhhLHfZEuLtA/manager_key
>>>>4: https://hangzhou.testnet.tezos.serokell.team/monitor/bootstrapped
>>>>5: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/context/constants
>>>>6: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/hash
>>>>7: https://hangzhou.testnet.tezos.serokell.team/chains/main/chain_id
>>>>8: https://hangzhou.testnet.tezos.serokell.team/chains/main/chain_id
>>>>9: https://hangzhou.testnet.tezos.serokell.team/chains/main/blocks/head/helpers/scripts/simulate_operation

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A type variable can be either universally ("for all x, then ...") or existentially quantified ("there exists some x, ...").

(If you're a maths persons, this corresponds to ∀x. x and ∃x. x, respectively)

In haskell, universally quantified type vars are represented with a forall:

head :: forall a. [a] -> Maybe a

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$ cabal run exe:coffer -- create diogo/google-work \
  --field user:dcastro@serokell.com \
  --field pw:123 \
  --field url:www.google.com

[SUCCESS] Entry created at '/diogo/google-work'

$ cabal run exe:coffer -- create diogo/google-home \

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import shapeless._
import shapeless.ops.record.Keys
import shapeless.ops.hlist.Selector
import shapeless.tag._

/**
  * Gets the name of a case class's field, in a type-safe way.
  * If the class does not have a field with the given name, the program won't compile.
  *
  * Kinda similar to C#'s `nameof` operator, but not bolted onto the language

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import shapeless._, record._
import io.circe._
import io.circe.syntax._
import io.circe.generic.encoding._

case class Person(name: String, age: Int)

object Person {
  implicit val encodePerson: Encoder[Person] =
    ReprObjectEncoder.deriveReprObjectEncoder.contramap { person =>

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This tutorial assumes you're already familiar with Haskell's kind system and extensions like DataKinds. If not, please read my blog post first </shameless-plug>.

Say you want to model a TCP connection, and it can be in either an "open" or "closed" status.

data Connection = MkConnection ...