CODEWITHSUNDEEP
elixir
codedownforwhat
codedownforwhat

Reputation: 173

How would a for loop be done with Elixir recursion?

I have a simple Go for loop and i want to learn how to do this with Recursion in Elixir. I don't really know how the recursion loop works at this time but i am working on that part! I also don't know if this is even the right way to do recursive functions.

package main

import "fmt"

func main() {
    for i := 0; i < 10000000; i++ {
        fmt.Println(i)
    }
}



defmodule Looping do
      def loops(i, e) when e <= 0 do
        IO.puts i + e
      end

      def loops(i, e) do
        IO.puts i + e
        loops(i, e + 1)
      end
    end 

    Looping.loops(1, 1)

Produces 1 + 1 + 1 on going in Elixir.

Martin over at the beginners slack channel suggested the following.

 1..1_000_000 |> Enum.each(&IO.puts/1)

Upvotes: 1

Views: 1382

Answers (4)

jrichocean
jrichocean

Reputation: 31

In your case using a range & a simple comprehension would work very well, but if you wanted to use recursion specifically you could do something like

defmodule SomeName do
    def addr(range), do: addr(Enum.to_list(range), 0)
    def addr([first|rest], sum), do: addr(rest, sum + first)
    def addr([], sum), do: sum
end

if you wanted to print each line you could throw an IO.inspect/1 in addr/2 to print out the sum like 

def addr([first|rest], sum) do
  IO.inspect(sum)
  addr(rest, sum + first)
end

Upvotes: 0

GavinBrelstaff
GavinBrelstaff

Reputation: 3069

Well ignoring the main stuff and running your elixir code in Iex I get an infinite ascending series that begins

1
2
3
4

which suggests you may have intended to stop when you arrive at 10000000 not at zero - thus tidying up your code we have:

defmodule Looping do
  def loops(e) when e == 10000000 do
    IO.puts e
  end

  def loops(e) do
    IO.puts e
    loops(e + 1)
  end
end 

Looping.loops(0)

Upvotes: 3

Sasha Fonseca
Sasha Fonseca

Reputation: 2313

I'm not exactly sure what you're looking for, but simulating a for loop with recursion in Elixir would look something like this:

def my_func(param1, 5), do: param1
def my_func(param1, count) do 
  my_func param1 * 2, count + 1
end

and you would call the function like this to run the loop from 1 to 5:

my_func(input_for_param1, 1)

I think your problem is that you still don't understand what recursion is and how Elixir (and Functional Programming languages) work. Try to first grasp these concepts (including pattern matching) and everything will come easier to you.

Another way to do a for loop would be by creating a construct for it through metaprogramming.

Upvotes: 2

Wobbley
Wobbley

Reputation: 914

There are a lot of simple recursion examples found here: http://elixir-lang.org/getting-started/recursion.html That also explain recursion and going through lists. What are you specifically after? Take a look at those and let me know if you are having a hard time figuring it out.

Upvotes: 0

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