Entries tagged with scala

Entry tags:

fp,
scala

one more slide show to watch

https://drive.google.com/file/d/0B5I9qM5f_1cfeGlMRUllMnRsZGc/view

Entry tags:

Короче, есть, скажем, пять вопросов для экзамена, каждый в нескольких вариантах; задача - изготовить варианты, чтобы они максимально различались. Ну типа всех возможных будет 5⁵, а мне надо 27, ну вот взять первые 27 из таких.

С таким смаком навалял это на скале. Типа такого:

    def findFurthest(current: List[Index])(collection: List[Index]) = collection.map(i => (distance(current)(i), i)).max(order)._2

    def sortByDistance(source: List[Index], target:List[Index] = Nil): List[Index] = source match {
      case Nil => target
      case more => {
        val furthest = findFurthest(target)(source)
        sortByDistance(source.filterNot(furthest==), furthest::target)
      }
    }

    val sorted = sortByDistance(allIndexes).reverse

Entry tags:

code sample,
scala

casual currying

no oop

I wanted this:

  def from(location: String) = {
    def loadTable(name: String, ignoring: String*) {
      def ignoringColumns(row: String Map String) = row.filterKeys(k => !(ignoring contains k))
      val src = Source.fromFile(s"$location/$name.csv").getLines().mkString("\n")
      
      val data = parseText(src) map ignoringColumns

      insertInto(name, data)
    }
  }

But has to write this:

  case class from(location: String) { self =>
    def loadTable(name: String, ignoring: String*): from = {
      // actually, the load order is opposite to deletion order    update(s"delete from $name")
      def ignoringColumns(row: String Map String) = row.filterKeys(k => !(ignoring contains k))
      val src = Source.fromFile(s"$location/$name.csv").getLines().mkString("\n")
      val data = parseText(src) map ignoringColumns toList

      insertInto(name, data)
      self
    }
  }

Using it like this:

  from(location).
  loadTable("users").
  loadTable("abusers","historyOfAbuse").
  loadTable("WMD","rocks","stones").
  loadTable("passwordAndKeys")

Entry tags:

scala

map3-like

Guys,

If I introduce

 def mix[X1,X2,X3](r1: Result[X1], r2: Result[X2], r3: Result[X3]): Result[(X1,X2,X3)] = {
    (r1,r2,r3) match {
      case (Good(x1),Good(x2),Good(x3)) => Good((x1,x2,x3))
      case (b1,b2,b3)                   => bad(b1, b2, b3)
    }
  }

So that instead of ((a,b),c) <- result1 andAlso result2 andAlso result3 we could write (a,b,c) <- mix(result1,result2,result3)

Do you think mix is a good name? Other alternatives would be ‘blend’, ‘join’…
It is similar to map3 in Haskell, but map3 comes from lambda, and it also applies a function.

I'll have it for a bunch of ns, not bothering with macros yet.

Entry tags:

scala

scala question

I wonder if we can have an implicit isomorphism of tuples, so that, say,

val (x,y,z) = ((x0,y0),z0) would involve the right transformation.

Would Be Cool.

Entry tags:

linear logic,
scala

some new code

  val _1:Unit = ()
  val _0: Nothing = ???

  case object None extends Maybe[Nothing] {
    override def ¬ : Maybe[Nothing] = Just(_0)
...

Entry tags:

figuring out...

So, I kind of discovered that the stuff I'm doing with my Result class looks suspiciously close to linear logic, e.g., in LL we have !(A&B)≡!A⊗!B, and I have Good(a) <*> Good(b) == Good((a,b)).

Moving on.

Similarly, there's some connection between Good[Either[A,B]] and Good(a:A) orElse Good(b:B).

Actually, what I have, it seems to be a coaffine logic, but well, who cares right now. We will see.

"If Γ,Δ⊢Θ, then Γ,!A,Δ⊢Θ, for any A " maps to

Good(a) foreach (f()) is the same as f().

"If Γ,!A,!A,Δ⊢Θ, then Γ,!A,Δ⊢Θ" maps to
Good(Good(a)).flatten == Good(a)

Not everything works. But is not it weird.

Entry tags:

DoggyEnglish

object DoggyEnglish {
  val meaningless = Set("name", "of", "the", "my", "your", "in", "what", "which", "was", "is")

  val synonyms = Set("city, town", "sibling, siblings", "job, work") .map {
    word => word.split(", ").toList
  } .collect {
    case main::tail => tail map (w => w -> main)
  } .flatten .toMap withDefault identity


  def simplifyQuestion(question: String) = {
    val noPunctuation = question.toLowerCase.replaceAll("[^a-z ]", "")
    val words = noPunctuation split " "
    val meaningfulWords = words filterNot meaningless
    val standardized = meaningfulWords map synonyms
    standardized mkString " "
  }

}

Entry tags:

funny stuff worth reading

http://dreamsongs.com/Files/worse-is-worse.pdf

Those were the days when I was debugging into the microcode of a stupid machine from Severodonetsk, which was losing interrupt stack trace from time to time, and so we were out of luck: I did lose some significant money on trying to fix this, but figure it was theoretically impossible.

Anyway, the source of inspiration is this: http://pchiusano.github.io/2014-10-13/worseisworse

Entry tags:

named tuple

Looking for a way to have and pass around named tuples, I'm kind of coming to a conclusion that this belongs to dependent types, roughly speaking. Or? Of course I'm only interested in Scala.

Entry tags:

just found a bug

I had a function checking if a collection of sets (of keys) has any common elements (if they do, have to add prefixes to the keys, to disambiguate). Imagine, I was just calculating their intersection. OMFG, in short.

Entry tags:

scala

one specific isomorphism

implicit def flatten1[A,B,C]:(((a:A,b:B),c:C)) => (a,b,c)
implicit def flatten2[A,B,C]:((a:A,(b:B,c:C))) => (a,b,c)

Of course we cannot seriously count on applying it implicitly to all kinds of tuples, but still... It's an isomorphism.

Entry tags:

a pretty interesting suggestion

I have an applicative Result class.

Result[A] <*> Result[B] gives a Result[(A,B)].

Now Csaba, who does not like this ascii soup, and does not like the phrase "tensor product" either (do you see tensors around here?) suggested to call this construct 'andAlso'.

I like this idea a lot.

  for ((name, dob) <- findValue(html, “user”) andAlso findValue(html, “date of birth”))

Entry tags:

scala

NPE in Scala

I'm REALLY tired of them.

Entry tags:

propaganda,
scala

obvious

src: http://www.toptal.com/scala/why-should-i-learn-scala

Entry tags:

wired funny

http://www.wired.com/2013/09/the-second-coming-of-java/all/

What I read here:
- Java's back
- Twitter uses Java
- Java is the fastest
- Bob Lee sees no choice
- Medvedev visited Twitter office 4 years ago

Any ideas what it was about?

Entry tags:

oops,
scala

akka

Sitting at SF Scala listening to Jonas Boner's talk. First I was absolutely impressed. Then Sergey W told me, wtf, no definitions, just vague talk. Kaboom.

Now I think I'm not much interested in Akka actually. Seems like a sleazy bs; and if you want to model pi-calculus, use Erlang.

Entry tags:

here "about categories"

my 6 chapters, math for programmers, categories from start to adjoints, with code samples in Scala.

Probably it's hard to read, formatting problems. Let me know if it's totally unreadable. Or if you think something should be fixed.

(updated)
http://orm-atlas2-prod.s3.amazonaws.com/pdf/455a990ff6b670a08f0ab9365538d284.pdf

robustness

one more slide show to watch

а вот и весь мой рендеринг

навалял в духе проекта Эйлер

casual currying

map3-like

scala question

some new code

figuring out...

DoggyEnglish

funny stuff worth reading

named tuple

just found a bug

one specific isomorphism

a pretty interesting suggestion

NPE in Scala

obvious

wired funny

akka

here "about categories"