adomokos

Type vs Data Constructors

In a data declaration, a type constructor is the thing on the left hand side of the equals sign. The data constructor(s) are the things on the right hand side of the equals sign. You use type constructors where a type is expected, and you use data constructors where a value is expected.

Data constructors

To make things simple, we can start with an example of a type that represents a colour.

data Colour = Red | Green | Blue

adomokos

DBUSER=db_user
DBPASSWD=db_password
DBNAME=some_db

THIS_FILE := $(lastword $(MAKEFILE_LIST))

.DEFAULT_GOAL := help

build-db: ## Builds the DB
	dropdb --if-exists --username $(DBUSER) $(DBNAME)

adomokos

Keybase proof

I hereby claim:

• I am adomokos on github.
• I am adomokos (https://keybase.io/adomokos) on keybase.
• I have a public key ASA8JcfM-KoBRcr5g7J-bADE-azTB3JtbjP0B6yn84UXygo

To claim this, I am signing this object:

adomokos

class CarElement
  def accept(visitor)
    raise NotImpelementedError.new
  end
end

module Visitable
  def accept(visitor)
    visitor.visit(self)
  end

adomokos

module ActiveRecord; class Base; end; end

# The AR Models Rails give you
class User < ActiveRecord::Base
  # These fields are defined dynamically by ActiveRecord
  attr_accessor :id, :full_name
end

class Discussion < ActiveRecord::Base
  # These fields are defined dynamically by ActiveRecord

adomokos

import Test.Hspec
import Test.QuickCheck
import Control.Exception (evaluate)
import qualified Data.Map as Map
import Data.List

mapping :: Map.Map Int String
mapping = Map.fromList [
  (1, "I"),
  (4, "IV"),

adomokos

package string_calculator

import (
        "github.com/stretchr/testify/assert"
        "strconv"
        "strings"
        "testing"
)

func Convert(params ...string) int {

adomokos

module StringCalculator where

import Test.Hspec
import Test.QuickCheck
import Control.Exception (evaluate)
import Data.List.Split (splitOn)

calculator' :: String -> Char -> Integer
calculator' x c = sum $ coerceString x c

adomokos

(ns change-maker.core-test
  (:require [clojure.test :refer :all]))

(def ^:dynamic *denominations* [25 10 5 1])

(defn best-match [value]
  (first (filter #(<= % value) *denominations*)))

(defn calculate-change [value product]
  (let [reducer (best-match value)]

adomokos

(ns keyword-like-function-test
  (:require [clojure.test :refer :all]))

(defn find-values
      [& {:keys [p1 p2] :or {p1 [0 0] p2 [1 1]}}]
  [p1 p2])

(deftest keyword-arguments-test
  (testing "when both of the arguments were passed"
    (is (= [4 15] (first (find-values :p1 [4 15] :p2 [3 21]))))