jrudolph

/*
 * This is the Towers of Hanoi example from the prolog tutorial [1]
 * converted into Scala, using implicits to unfold the algorithm at
 * compile-time. 
 * 
 * [1] http://www.csupomona.edu/~jrfisher/www/prolog_tutorial/2_3.html
 */

object TowersOfHanoi {
  import scala.reflect.Manifest

retronym

class A
class A2 extends A
class B

trait M[X]

//
// Upper Type Bound
//
def upperTypeBound[AA <: A](x: AA): A = x

retronym

scala> :power
** Power User mode enabled - BEEP BOOP      **
** scala.tools.nsc._ has been imported      **
** New vals! Try repl, global, power        **
** New cmds! :help to discover them         **
** New defs! Type power.<tab> to reveal     **

scala> val s = repl.stringToCompilerType("scala.Some")           
s: repl.compiler.Type = object Some

codedot

x ∈ Λ;                                                                          Лямбда-выражения строятся из переменных
M, N ∈ Λ ⇒ λx.M ∈ Λ ∧ M N ∈ Λ;                                                  с помощью абстракций и аппликаций;
(M) = M, M N P = (M N) P.                                                       причем аппликация лево-ассоциативна.

x[x := P] = P;                                                                  Подстановка заменяет вхождения переменной на другое выражение,
y[x := P] = y;                                                                  но только если переменная совпадает,
(λx.M)[x := P] = λx.M;                                                          при этом связанные переменные не подлежат подстановке;
(λy.M)[x := P] = λy.M[x := P];                                                  операция подстановки через абстракции
(M N)[x := P] = M[x := P] N[x := P].                                            и аппликации проходит выражение рекуррентно.

defunkt

All You Zombies

2217 Time Zone V (EST) 7 Nov. 1970--NTC-- "Pop's Place": I was polishing a brandy snifter when the Unmarried Mother came in. I noted the time---10:17 P. M. zone five, or eastern time, November 7th, 1970. Temporal agents always notice time and date; we must.

The Unmarried Mother was a man twenty--five years old, no taller than I am, childish features and a touchy temper. I didn't like his looks---I never had---but he was a lad I was here to recruit, he was my boy. I gave him my best barkeep's smile.

Maybe I'm too critical. He wasn't swish; his nickname came from what he always said when some nosy type asked him his line: "I'm an unmarried mother." If he felt less than murderous he would add: "at four cents a word. I write confession stories."

If he felt nasty, he would wait for somebody to make something of it. He had a lethal style of infighting, like a female cop---reason I wanted him. Not the only one.

viktorklang

trait Enum { //DIY enum type
  import java.util.concurrent.atomic.AtomicReference //Concurrency paranoia

  type EnumVal <: Value //This is a type that needs to be found in the implementing class

  private val _values = new AtomicReference(Vector[EnumVal]()) //Stores our enum values

  //Adds an EnumVal to our storage, uses CCAS to make sure it's thread safe, returns the ordinal
  private final def addEnumVal(newVal: EnumVal): Int = { import _values.{get, compareAndSet => CAS}
    val oldVec = get

copumpkin

module Prime where

open import Coinduction

open import Data.Empty
open import Data.Nat
open import Data.Nat.Properties
open import Data.Nat.Divisibility
open import Data.Fin hiding (pred; _+_; _<_; _≤_; compare)
open import Data.Fin.Props hiding (_≟_)

klapaucius

Ответ на вопрос в этом посте.

Для начала слегка модифицируем код, чтоб он компилировался.

import qualified Data.List.Stream as S
import qualified Data.Vector.Unboxed as U

f n = let arr = U.enumFromTo 1 n 
      in S.sum $ S.map (\i -> arr U.! (i `rem` n)) $ S.unfoldr (\i -> if i < n then Just (i, i+1) else Nothing) 0

SethRobertson

On undoing, fixing, or removing commits in git

The official and authoritative source for this document has moved. Please update your bookmarks.

You can still use the comments at the bottom of the page to register comments even for the new official location.

arosien

F[A]           // A is a Functor
M[A]           // A is a Monad
fa: F[A], a: A // variables used below

fa1 |+| fa2 // binary append (SemiGroup)
fa1  >| fa2 // map           (Functor)
fa1 >>= fa2 // flatmap       (Bind)
fa1 |>| fa2 // foreach       (Each)

fa <**> fb { (a, b) => c }                       // apply, produces F[C]