Recursion is considered as to be important in functional programming. You can now safely call sum with a list that has 10,000 elements, 100,000 elements, etc., and it will work just fine without blowing the stack. We say a function is tail recursive when the recursive call is the last thing executed by the function. To help in your efforts, the next lesson will show more examples of tail-recursive for different types of algorithms. Java Project Tutorial - Make Login and Register Form Step by Step Using NetBeans And MySQL Database - Duration: 3:43:32. No. This is a two part series on Recursion, please complete part-1 before you proceed further. Explaining tail recursion in scala with proper example. The tail recursive functions considered better than non tail recursive functions as tail-recursion can be optimized by compiler. Earlier this week, I gave a talk about Scala with Bill Venners and David Pollak.In my slides, I had an example of a factorial function in Scala and in Java.I made that point that not only is Scala usually almost as fast as Java, but sometimes it is even faster. On Stack Overflow, Martin Odersky explains tail-recursion in Scala: “Functions which call themselves as their last action are called tail-recursive. You signed in with another tab or window. In this tutorial, we’ll show how Scala’s tail recursion optimizations can address this issue by reducing the call stack to just one frame. output file. Tail Recursion in Scala. The identity value for a product algorithm is 1. For instance, in the Sum example below, when I get to the Nil element in a List, I return 0and let the recursive method calls u… The Scala compiler detects tail recursion and replaces it with a jump back to the beginning of the function, after updating the function parameters with the new values ... as long as the last thing you do is calling yourself, it’s automatically tail-recursive (i.e., optimized).”. That is, it simply means function calling itself. From the “Functional” cartoon on xkcd.com. Learn more. This article presents a really good simple example of how tail recursion in the source code is translated to a loop in the byte code. Appendix: Recursion is great, but check out Scala’s fold and reduce! I will start with a very simple example; by summing a list of integers with fold. ... Scala Example: We’ve got a sequence of first names and a sequence of last names, and we want to put them together to make people. Scala supports Recursion very well. I hope you already understand the notion of a head and the tail. Learn more. ), Note: The upper limit of a Scala Int is 2,147,483,647, so at some point you’ll create a number that’s too large for that. You can always update your selection by clicking Cookie Preferences at the bottom of the page. Overview. In this tutorial on tail recursion in Scala, we will learn about tail recursion in depth along with examples. Case 3: Tail Recursion – Optimized by the compiler. Let us understand using the simple factorial example. ... A fairly standard example is tree traversal: the recursion is bounded to the height of the tree, ... tail-recursive functions for tree exploration are far more complicated than non tail-recursive ones. It is used by defining the name of the list followed by the keyword List and in parentheses the values of the List separated by comma. Head recursion carries the risk of a stack overflow error, should the recursion go quite deep. tries to match the incoming List(1,2,3,4) with something in the form h::tail, which means "a list with a single element head and a list tail".Using the :: operator ensures that h is considered a single element.. For example: val myList = List(1,2,3,4,5,6,7,8,9) A list of examples of how to properly implement tail call optimization in scala. Learn more, We use analytics cookies to understand how you use our websites so we can make them better, e.g. This is a demonstration of a tree-traversal algorithm to calculate the size of a binary tree, in Scala. Submitted by Shivang Yadav, on September 04, 2019 . the expected output. Now that you are a tail recursion expert, let’s look at some code: (If that’s not big enough, use a BigInt.). The second parameter is new. various situation using scala. The 'LazyList' type (previously known as 'Stream' in Scala) is used to describe a potentially infinite list that evaluates only when necessary ('lazily'). A tail-recursive function is just a function whose very last action is a call to itself. All they’ll see is sum’s signature: Tail-recursive algorithms that use accumulators are typically written in the manner shown, with one exception: Rather than mark the new accumulator function as private, most Scala/FP developers like to put that function inside the original function as a way to limit its scope. We also looked at Scala’s slice-and-dice technique and how to split the list so that we can visit each element. 2. One important difference is that in the case of gcd, we see thatthe reduction sequence essentially oscillates. 1) Leave the original function signature the same. Generally speaking, we can separate recursion problems into head and tail recursion. But on a List the cons method is more efficient than the append method so it is usually better to build-and-reverse.. Q2. I have compiled and tested the programs using Scala compiler version 2.11.6. The identity value for a sum algorithm is 0. A special type of recursion which does the recursive call as the last thing in the execution of the code. Scala automatically optimizes tail recursive functions by converting the recursion into a loop. Tail recursion is little tricky concept in Scala and takes time to master it completely. Is my rec function tail recursive? In this tutorial, we will learn how to create trampoline tail recursive function by making use of utilities that Scala provides for tail recursions in the package scala.util.control.TailCalls._. One reason for this is that the Scala compiler can perform tail recursion optimizations on your code. Overview. In this example, we can see the fib_tail call being applied in the last line of code. You can reverse the List before it is returned, as @Mahesh Chand Kandpal has pointed out, or you can build the list with the append method, accum :+ x, instead of the pre-pend ("cons") method, x :: accum.. Convert normal recursion to tail recursion (4) I was wondering if there ... but a recursive implementation won't be efficient even with tail-recursion. A list of examples of how to properly implement tail call optimization in scala - supalogix/scala-tail-recursion-example If the command above does not produce output then the expected input yields Here’s the source code for the new version of sum: Note that this “seed” value is the same as the identity value I wrote about in the previous recursion lessons. 3. Scala Best Practices. takes an input file as an argument and writes its results to standard Here's a typical, if trivial, example of the kind of thing that new Scala programmers want to do: val data = List(0.1, 0.4, 0.2, 0.7, - 0.1, 1.1, 0.5) { var sum = 0.0 Recursion is a method which breaks the problem into smaller sub problems and calls itself for each of the problems. This article presents a really good simple example of how tail recursion in the source code is translated to a loop in the byte code. download the GitHub extension for Visual Studio. This example is not tail recursive because when the recursive call is made, the function needs to keep track of the multiplication it needs to do with the result after the call returns. val numbers = List(5, 4, 8, 6, 2) numbers.fold(0) { (z, i) => a + i } // result = 25 The fold method for a List takes two arguments; the start value and a function. “Hmm,” you might say, “if I understand Mr. Odersky’s quote, the sum function you wrote at the end of the last lesson sure looks tail-recursive to me”: “Isn’t the ‘last action’ a call to itself, making it tail-recursive?”. gcd(14, 21)is evaluated as follows: Now, consider factorial: factorial(4)is evaluated as follows: What are the differences between the two sequences? In this tutorial, we will learn how to use the tail function with examples on collection data structures in Scala.The tail function is applicable to both Scala's Mutable and Immutable collection data structures.. A recursive function is said to be tail recursive if the recursive call is the last thing done by the function. Reading Odersky's "Programming in Scala 2nd edition", it seems that Scala (now) detects tail-recursion automatically. Instead we use the List as a higher structure. Use of recursion in Scala when run in the JVM (4) From searching elsewhere on this site and the web, tail call optimization is not supported by the JVM. In one case, when I’m handling the situation of being at the last element of the collection, I do some “ending” operation. the - tail recursion scala examples . Tail recursion implementation via Scala: Using regular recursion, each recursive call pushes another entry onto the call stack. Scala Recursion Example (Tail Recursion) - Dot Net Perls. (Go ahead and test it! We saw how recursive calls and associated context are remembered on stack frames and the need for tail recursion. Work fast with our official CLI. directory. The first proof is already in the code. Scala tail recursion by example A tail recursive function in Scala is remedy if your recursive functions causes a stack overflow. We use essential cookies to perform essential website functions, e.g. With change () we compute possible arrangements of coins until we meet our goal amount. Example : Tail-recursive algorithms that use accumulators are typically written in the manner shown, with one exception: Rather than mark the new accumulator function as private , most Scala/FP developers like to put that function inside the original function as a way to limit its scope. In the directory FizzBuzz, you will find the following files: Compile FizzBuzz.scala with the following command, Run the application with the following command, Test the correctness of the program with the following command. example - tail recursion scala . For some reason I didn't use it very often in Ruby, but I use it all the time with Scala. Example: How to make sum tail-recursive. The third step is to modify the algorithm of the newly-created function to use the accumulator parameter. Functional Programming, Simplified (Scala edition), Functional Programming Background (Section), Scala and Functional Programming (Section), A First Look at “State” in Functional Programming, A Functional Game (With a Little Bit of State), Scala/FP Idiom: Update as You Copy, Don’t Mutate, A Quick Review of Scala’s for-expressions (for-comprehensions), How to Write a Scala Class That Can Be Used in a `for` Expression, How to Create a Scala Sequence Class to be Used in a ‘for’ Expression, How to Make Sequence Work in a Simple Scala `for` Loop, How To Make Sequence Work as a Single Generator in a `for` Expression, How to Enable Filtering in a Scala `for` Expression, How to Enable the Use of Multiple Generators in a Scala `for` Expression, Lessons that didn’t fit in the printed book, Using Scala Methods As If They Were Functions (Eta Expansion), How to Write Scala Functions That Take Functions as Input Parameters, Functional Programming, Simplified (Introduction), How to Write a ‘map’ Function in Scala, Scala/FP: Pure Function Signatures Tell All, Goals, Part 1: “Soft” Goals of This Book, Recursion: How to Write a ‘sum’ Function in Scala, A Note About Expression-Oriented Programming, How to Write and Use Scala Functions That Have Multiple Parameter Groups, Goals, Part 2: Concrete Goals of This Book, Functional Programming is Like Unix Pipelines, Recursion: How Recursive Scala Function Calls Work, Partially-Applied Functions (and Currying) in Scala, Recursion: Visualizing the recursive `sum` Function, Recursion: A Conversation Between Two Developers, Introduction to ScalaCheck, Part 2 (A more complicated example), Scala: The Differences Between `val` and `def` When Creating Functions, Appendix: Scala `for` expression translation examples, On Using `def` vs `val` To Define Abstract Members in Scala Traits. I’m usually not smart enough to write a tail-recursive function right away, so I usually write my algorithms using simple recursion, then convert them to use tail-recursion. For: In the for-loop we try to add coins. A solution. Now that you know the current approach isn’t tail-recursive, the question becomes, “How do I make it tail-recursive?”. This, however, is just a mnemonic. We saw examples where tail recursion enables TCO. If you have a list like (5,4,3,2,1,0) , the first element is the head, and the rest is the tail. The fourth step in the process is to modify the original function to call the new function. Fortunately a Long goes to 2^63-1 (which is 9,223,372,036,854,775,807), so that problem is easily remedied. Tail position means the caller returns the result from its callee directly. Overview. (Don’t tell anyone, but I prefer the first approach; I think it reads more easily.). The easiest way to explain this is to show the code for the solution, and then explain the changes. The main goal of this lesson is to solve the problem shown in the previous lessons: Simple recursion creates a series of stack frames, and for algorithms that require deep levels of recursion, this creates a StackOverflowError (and crashes your program). This annotation won’t compile unless the function is tail-recursive. Recursion is quite common in functional programming and provides a natural way to describe many Algorithms. And thus for example the model browser can then do some optimization on those useless stack frames. Each program It goes from one call t… If that’s what you’re thinking, fear not, that’s an easy mistake to make. We only add equal or larger coins. Tail recursion in Scala is a recursive method that was created to make the Classic recursion more efficient. That is, it simply means function calling itself. GitHub is home to over 50 million developers working together to host and review code, manage projects, and build software together. def listLength1(list: List[_]): Int = { if (list == Nil) 0 else 1 + listLength1(list.tail) } var list1 = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) var list2 = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) 1 to 15 foreach( x => list2 = list2 ++ list2 ) println( listLength1( list1 ) ) … If some action is repetitive, we can call the same piece of code again. The tail method returns a collection consisting of all elements except the first one.. As per the Scala documentation, the definition of the tail method is as follows: The JVM output shows the sum method is called once for each step in the recursion, so it’s clear that the JVM feels the need to create a new instance of sum for each element in the collection. Of course you can also name the inner function whatever you’d like to call it. The truth is that :: in Scala is also a class derived from List which is constructed passing a single element and a list. Keep the original function signature the same (i.e., Create a second function by (a) copying the original function, (b) giving it a new name, (c) making it, Modify the second function’s algorithm so it uses the new accumulator. they're used to gather information about the pages you visit and how many clicks you need to accomplish a task. If you don’t like the name accumulator for the new parameter, it may help to see the function with a different name. November 11, 2018 November 12, 2018 / thehadoopblog. Scala automatically optimizes tail recursive functions by converting the recursion into a loop. If for some reason you don’t believe the compiler, a second way to prove this is to add some debug code to the new sum function, just like we did in the previous lessons. Intent: To repeat a computation without using mutable state and without overflowing the stack. A Recursive function is the function which calls itself. When you write your recursive function in this way, the Scala compiler can optimize the resulting JVM bytecode so that the function requires only one stack frame — as opposed to one stack frame for each level of recursion! Martin Odersky explaining tail recursion on Stack Overflow, When that function call returns, add its value to. This repository contains examples of how to use tail call optimization in Personally I prefer currentSum for this algorithm, but you’ll often hear this approach referred to as using an “accumulator,” which is why I used that name first. The tail recursive functions better than non tail recursive functions because tail-recursion can be optimized by compiler. A tail recursive function in Scala is remedy if your recursive functions causes a stack overflow. And thus for example the model browser can then do some optimization on those useless stack frames. If a recursive function is not tail-recursive, each time the function is… If there are much recursive function calls it can end up with a huge stack. A common pattern used to make a recursive function that “accumulates a result” into a tail-recursive function is to follow a series of simple steps: Let’s jump into an example to see how this works. Here’s the source code: Here’s a description of how that code works: The result of this approach is that the “last action” of the sumWithAccumulator function is this call: Because this last action really is a call back to the same function, the JVM can optimize this code as Mr. Odersky described earlier. Furthermore, tail recursion is a great way if to make your code faster and memory constant. If nothing happens, download the GitHub extension for Visual Studio and try again. One way to “prove” that the sum algorithm is not tail-recursive is with the “stack trace” output from the previous lesson. With Scala you can work around this problem by making sure that your recursive functions are written in a tail-recursive style. First, consider gcd, a method that computes the greatest common divisor oftwo numbers. The identity value for a string concatenation algorithm is, Showed how to write a tail-recursive function, Showed a formula you can use to convert a simple recursive function to a tail-recursive function. We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. A solution. The two implementations are recursive, as one should try to do in functional programming, but the first implementation is not tail-recursive, and the second is. The tail method returns a collection consisting of all elements except the first one.. As per the Scala documentation, the definition of the tail method is as follows: In fact, they won’t know that the internal algorithm uses a seed value. Each directory has Scala Recursion Example (Tail Recursion) - Dot Net Perls. The base case is needed so that the process eventually gets terminates. It contains the following programs. When the recursion is completed, the application has to pop each entry off all the way back down. Observe the stack frame for tail recursion step by step: stack popped up: When N = 20, the tail recursion has a far better performance than the normal recursion: Update 2016-01-11. I have placed the programs in dedicated directories. Use Git or checkout with SVN using the web URL. Recursion could be applied to problems where you use regular loops to solve it. We use optional third-party analytics cookies to understand how you use GitHub.com so we can build better products. Although sum(tail) is at the end of the second case expression, you have to think like a compiler here, and when you do that you’ll see that the last two actions of this function are: When I make that code more explicit and write it as a series of one-line statements, you see that it looks like this: As shown, the last calculation that happens before the return statement is that the sum of x and s is calculated. they're used to log you in. This lesson covered the basics of converting a simple recursive function into a tail-recursive function. It’s the “accumulator” that I mentioned earlier. Tail Recursion – SCALA. Tail recursion implementation via Scala: Key example. Although the previous lesson showed that algorithms with deep levels of recursion can crash with a StackOverflowError, all is not lost. Try computing pascal(30, 60), for example. @tailrec shouldn't be necessary. To begin the process of converting the recursive sum function into a tail-recursive sum algorithm, leave the external signature of sum the same as it was before: Now create the second function by copying the first function, giving it a new name, marking it private, giving it a new “accumulator” parameter, and adding the @tailrec annotation to it. (a) a scala file, (b) an input file, and (c) and an output file. Let us understand it by a example: Example : (5) ... Tail recursion is when recursive calls all appear in tail position. There is no need to keep record of the previous state. (More on this shortly. Before we get into Tail recursion, lets try to look into recursion. In this example, we can see the fib_tail call being applied in the last line of code. For a “sum” algorithm a name like runningTotal or currentSum may be more meaningful: I encourage you to use whatever name makes sense to you. This is a demonstration of a tree-traversal algorithm to calculate the size of a binary tree, in Scala. Tail recursion in Scala is a recursive method that was created to make the Classic recursion more efficient. I know I want to do something with a collection of data elements. The benefit of this is that other programmers won’t have to provide the initial seed value. The output files represent the expected output for the program in their Let’s look at an example recursive function in scala. List Processing in Scala. Q1. If you’re not 100% sure that you believe that, there are a few ways you can prove it to yourself. Scala automatically removes the recursion in case it finds the recursive call in tail position. A recursive function is said to be tail recursive if the recursive call is the last thing done by the function. Calculating List Length When you make this change, the final code looks like this: Feel free to use either approach. When you compile this code with the @tailrec annotation and the compiler doesn’t complain, you know that the compiler believes the code is tail-recursive. Before moving on, notice that the data type for the accumulator (Int) is the same as the data type held in the List that we’re iterating over. If nothing happens, download Xcode and try again. Now let’s prove that the compiler thinks this code is tail-recursive. Scala Language Tail Recursion Example. It began with LISP, which saw symbol manipulation (i.e., processing lists of symbols) as the key to artificial intelligence. Scala Tail recursion. Furthermore, tail recursion is a great way if to make your code faster and memory constant. This code includes a few ScalaTest tests, including one test with a List of 100,000 integers. Now that you are a tail recursion expert, let’s look at some code: In those lessons I noted: It has the same function signature as the previous version of sum. We introduce the change () and display () functions. Millions of developers and companies build, ship, and maintain their software on GitHub — the largest and most advanced development platform in the world. A special type of recursion which does the recursive call as the last thing in the execution of the code. import scala.annotation.tailrec object SumTailRecursive extends App { // call sum println(sum(List.range(1, 10))) // the tail-recursive version of sum def sum(list: List[Int]): Int = { @tailrec def sumWithAccumulator(list: List[Int], currentSum: Int): Int = { list match { case Nil => { val stackTraceAsArray = Thread.currentThread.getStackTrace stackTraceAsArray.foreach(println) … If you alter the input files then you must make an associated change to the Let’s compare the evaluation steps of the application of two recursivemethods. A second way to prove that sum isn’t tail-recursive is to attempt to tag the function with a Scala annotation named @tailrec. output. Here's an implementation of gcdusing Euclid's algorithm. Submitted by Shivang Yadav, on September 04, 2019 . optimization - than - tail recursion scala examples . Make recursive functions tail-recursive. Within the function I usually have two branches: 3.1. Here’s the source code for a full Scala App that shows this approach: Note: You can find this code at this Github link. When doing this, the thought process is, “Don’t expose the scope of sumWithAccumulator unless you want other functions to call it.”. (More on this later in this lesson.). in the following, what is that last call? If a recursive function is not tail-recursive, each time the function is… But the answer is no, this function is not tail-recursive. If you attempt to add the @tailrec annotation to sum, like this: the scalac compiler (or your IDE) will show an error message like this: This is another way to “prove” that the Scala compiler doesn’t think sum is tail-recursive. I get a lot of output, but if I narrow that output down to just the sum-related code, I see this: As you can see, although the List in the code has 10 elements, there’s only one call to sum, and more importantly in this case, only one call to sumAccumulator. package com. The List is implemented in the scala.collection.immutable library but importing the library is not necessary. Function with a StackOverflowError, all is not lost menos que un método definitivo! For some reason I did n't use it all the time with Scala for the new.. In Ruby, but I prefer the first approach ; I think it reads easily. Usually take this collection as an argument of gcd, a method that computes the greatest divisor. Euclid 's algorithm same function signature the same piece of code again Form. Reason I did n't use it very often in Ruby, but I prefer the first element is last. Of course you can prove it to yourself you know the current approach isn’t tail-recursive, the becomes! Is the last thing in the scala.collection.immutable library but importing the library is not tail-recursive is with “stack! Website functions, e.g the rest is the function means scala tail recursion list example caller returns the result its. Calls it can end up with a List of 100,000 integers separate recursion problems into head and need! Think about it like this: Feel free to use the accumulator.! You Don’t like the name accumulator for the program in their directory calculating List Length this is to show code! With change ( ) functions get into tail recursion is a method that was created to your., fear not, that’s an easy mistake to make Cookie Preferences the... Piece of code the first approach ; I think it reads more easily. ) lets try look. That your recursive functions better than non tail recursive functions causes a stack Overflow, Martin explains! Appendix: recursion is a call to itself Scala’s fold and reduce ( we... A Long goes to 2^63-1 ( which is 9,223,372,036,854,775,807 ), call same. To be tail recursive functions scala tail recursion list example a stack Overflow, Martin Odersky explains tail-recursion in.! Trace” output from the previous state Desktop and try again way to prove that sum isn’t tail-recursive is the. Of sumWithAccumulator unless you want other functions to call the same function signature the same piece code. By compiler using NetBeans and MySQL Database - Duration: 3:43:32 in the scala.collection.immutable library importing! That’S what you’re thinking, fear not, that’s an easy mistake to make your code faster and constant! Explain this is that the Scala compiler can perform tail recursion ) - Dot Net Perls from previous... ) and display ( ) functions repository contains examples of how to properly implement tail call optimization in various using! Seems to be important in functional programming and provides a natural way to “prove” that Scala! If you have a List the cons method is more efficient than the append method so it is better! Around this problem by making sure that your recursive functions by converting the into! Very last action are called tail-recursive memory constant example - tail recursion -. Using mutable state and without overflowing the stack is tail recursive functions causes a stack Overflow, Odersky. Won’T compile as shown, so that problem is easily remedied to solve it piece of code position. This collection as an argument and writes its results to standard output files! Output files represent the expected output for the program in their directory isn’t tail-recursive is to the. Can see the fib_tail call being applied in the scala.collection.immutable library but importing the is... Code, manage projects, and the tail value to Git or checkout with SVN the. Than non tail recursive if the recursive call is the last thing done by function! 1 ) Leave the original function signature as the key to artificial intelligence associated context are on. - tail recursion ) - Dot Net Perls by clicking Cookie Preferences at the bottom of the for! Of tail-recursive for different types of Algorithms part-1 before you proceed further ). Instead we use the accumulator parameter scala tail recursion list example see the function from the previous version of sum now that believe! Your efforts, the first approach ; I think it reads more easily. ) you need to accomplish task..., processing lists of symbols ) as the previous state attempt to tag the function method I! Lesson will show more examples of tail-recursive for different types of Algorithms Login and Form... Thinking, fear not, that’s an easy mistake to make the Classic recursion more efficient the! Writes its results to standard output into tail recursion is when recursive calls appear. Furthermore, tail recursion optimizations on your code faster and memory constant speaking, we can call the.... To yourself, use a BigInt. ) make an associated change to the files! Add coins the caller returns the result from its callee directly no aplica la optimización de llamadas de cola menos... Is just a function whose very last action are called tail-recursive will start with a name! Difference is that other programmers won’t have to provide the initial seed value a higher.. On those useless stack frames function will usually take this collection as an argument and writes its results to output. Basics of converting a simple recursive function calls it can end up with a collection of elements. Returns the result from its callee directly how many clicks you need keep! Be important in functional programming and provides a natural way to “prove” that the algorithm... So that we can visit each element binary tree, in Scala the Scala compiler can perform recursion... Expected input yields the expected input yields the expected output for the program in their directory of... My function will usually take this collection as an argument and writes its results to standard output you’re 100! If the command above does not produce output scala tail recursion list example the expected input yields the expected output for the parameter! You’D like to call it Scala ’ s slice-and-dice technique and how many clicks you need to accomplish a.. Let’S prove that the process is, “Don’t expose the scope of sumWithAccumulator unless want... Part-1 before you proceed further of recursion which does the recursive call tail... Recursive when the recursive call pushes another entry onto the call stack of sumWithAccumulator you! In tail position into tail recursion optimizations on your code faster and memory constant includes a ScalaTest. Said to be tail recursive if the command above does not produce output then expected! Types of Algorithms how tail recursion is quite common in functional programming and provides a natural to., lets try to scala tail recursion list example coins previous state the time with Scala you can work this! To artificial intelligence subproblems and calls itself for each of the newly-created function to use tail call optimization various... Said to be important in functional programming and provides a natural way to many! Mylist = List ( 1,2,3,4,5,6,7,8,9 ) Overview update your selection by clicking Preferences... My function will usually take this collection as an argument alter the input files then you must an... In a tail-recursive style their directory checkout with SVN using the web URL in. Check out Scala’s fold and reduce Scala Best Practices clicking Cookie Preferences at bottom! That’S an easy mistake to make your code Ruby, but check out Scala’s fold and reduce I know want. A sum algorithm is not tail-recursive is to attempt to tag the function I have... Before we get into tail recursion in depth along with examples explain this is that last call,!