https://github.com/shpota/do-while-loop-implementation-in-scala

'Handmade' implementation of DO-WHILE loop using only build-in Scala features.
https://github.com/shpota/do-while-loop-implementation-in-scala

example loop scala scala-example scala-features

Last synced: 18 days ago
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'Handmade' implementation of DO-WHILE loop using only build-in Scala features.

• Host: GitHub
• URL: https://github.com/shpota/do-while-loop-implementation-in-scala
• Owner: Shpota
• Created: 2016-10-06T17:46:01.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2016-10-16T20:12:27.000Z (over 8 years ago)
• Last Synced: 2025-01-08T12:02:26.871Z (21 days ago)
• Topics: example, loop, scala, scala-example, scala-features
• Language: Scala
• Homepage:
• Size: 7.81 KB
• Stars: 2
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
'Handmade' implementation of DO-WHILE loop in Scala

===================================================

Scala is wery powerfool language. Almost every scala feature may be implemented using only built in language features. I want to demonstrate how to implementat a loop.

Scala already has ```do-while``` loop, that is why I'm using ```repeat-until``` naming in the example.

We want to implement something like this:

```scala

repeat {

  // do some stuff

} until (condition)

```

To achive this goal we have to declare a function ```repeat``` which will repeat some actions. The second part is the  function ```until```. It will have ```condition``` as an argument to contorol the loop. Finally we need to wire both the functions. To be able to do that we'll declare ```until``` function as a method inside the object returned by ```repeat``` function. 

Sounds complicated, let's take a look on the code:

```scala

def repeat(command: => Unit) = {

  new {

    def until(condition: => Boolean): Unit = {

      command

      if (condition)

        until(condition)

      else ()

    }

  }

}

```

As you can see we have anonymous object inside function body and one more functions inside. That means that the object will be returned by ```repeat``` so we can invoke ```until``` directly after ```repeat``` invocation.

The function body itself is pretty simple. First we invoke ```command``` and then depending on ```condition``` we decide if we need to terminate or we need to make one more recursive call.

Let's see how it works on example:

```scala

var i = 0

repeat {

  println("Iteration #" + i)

  i = i + 1

} until (i < 5)

```

The output as you may expect will be:

```

Iteration #0

Iteration #1

Iteration #2

Iteration #3

Iteration #4

```

## How to run the code

1) You need to have Scala SDK installed on your machine

2) Run Scala console

```bash

$ scala

```

3) Run the code

```bash

scala> :load loop.scala

```