Formulae.Combinators.permutations/2 wants an actual integer and not a variable

user_1175166 0
Viewed 21

The code:

require Formulae.Combinators

def permutations(trains, train_stations)
    when is_list(trains) and
          is_list(train_stations) do
  number_of_trains = length(trains)
  Formulae.Combinators.permutations(train_stations, number_of_trains)
end

The error:

** (ArgumentError) ranges (first..last) expect both sides to be integers, got: 
{:number_of_trains, [line: 86], nil}..1
(elixir 1.10.2) lib/range.ex:63: Range.new/2
expanding macro: Formulae.Combinators.permutations/2
lib/trains.ex:86: Trains.permutations/2

But https://hexdocs.pm/formulae/Formulae.Combinators.html says the in permutations(l, n) n should be an integer and length(trains) returns an integer. Formulae.Combinators.permutations(train_stations, 2) works fine.

What is my mistake? How can I fix it?

elixir
1 Answers
user_20352620
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