While Loop in Elixir by re-assigning a value to a variable

Question

I want to encode this algorithm In Elixir:

var name = generate_name();
while (check_if_exists(name)) {
  name = generate_name();
}

I can't encode that the same way in Elixir because there must more idiomatic and functional way. How can I do that then?

One approach is to try to convert your algorithm into map/list processing. Can either generate_name() or check_if_exists() be implemented as processing a map/list - say a map/list of possible/existing names? Two ways forward and key lookup in a map elixir-lang.org/getting-started/keywords-and-maps.html or a database query using Ecto hexdocs.pm/ecto/Ecto.Query.html — GavinBrelstaff
– GavinBrelstaff, Commented Apr 11, 2017 at 5:35

Community · Accepted Answer · 2017-05-23 12:17:39Z

8

Elixir is an Immutable programming language. That means you cannot modify the value of variable, only re-bind it. Hence, the classic while-loop doesn't exist in Elixir.

But, you can implement this using recursion:

def get_name do
  name = generate_name()

  case check_if_exists(name) do
    true  -> get_name()
    false -> name
  end
end

edited May 23, 2017 at 12:17

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answered Apr 11, 2017 at 4:19

Sheharyar

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5 Comments

Aleksei Matiushkin Over a year ago

Guidelines suggest using case for 3+ clauses only: if check_if_exists(name), do: get_name(), else: name.

Incerteza Over a year ago

I can very well change a value of a variable in Elixir

sevenseacat Over a year ago

no, you cannot change the value of a variable - you can only rebind it to a different value.

Fred the Magic Wonder Dog Over a year ago

If/else is just a macro for the case statement with true/false code above.

Sheharyar Over a year ago

I chose case instead of if-else because I like it more, even though it's a macro on top of case just like @FredtheMagicWonderDog said

Patrick Oscity · Accepted Answer · 2017-11-16 23:59:32Z

6

Another possibility is to create an infinite stream of names, then find the first name that is available:

Stream.repeatedly(&generate_name/0)
|> Enum.find(&check_if_exists/1)

edited Nov 16, 2017 at 23:59

answered Apr 11, 2017 at 9:26

Patrick Oscity

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