Why doesn't this functional call match in Elixir?

Question

What about this function is wrong ?

  @spec of_rna(String.t()) :: {atom, list(String.t())}
  def of_rna(rna) do
        data = rna |> String.codepoints 
                   |> Enum.chunk_every(3)
                   |> Enum.map(fn(x) -> Enum.join(x) end)
        do_rna(data, [])
  end

  def do_rna([head | tail] , Result) do
        case  @proteins[head] do
                STOP -> {:ok, Result}
                _ -> do_rna(tail, Result ++ [@proteins[head]])
        end
  end

The test I am using is:

test "stops translation if stop codon present" do
    strand = "AUGUUUUAA"
    assert ProteinTranslation.of_rna(strand) == {:ok, ~w(Methionine Phenylalanine)}
  end

The error I am seeing is:

1) test stops translation if stop codon present (ProteinTranslationTest)
     protein_translation_test.exs:67
     ** (FunctionClauseError) no function clause matching in ProteinTranslation.do_rna/2

     The following arguments were given to ProteinTranslation.do_rna/2:

         # 1
         ["AUG", "UUU", "UAA"]

         # 2
         []

     code: assert ProteinTranslation.of_rna(strand) == {:ok, ~w(Methionine Phenylalanine)}
     stacktrace:
       protein_translation.exs:37: ProteinTranslation.do_rna/2
       protein_translation_test.exs:69: (test)

I don't understand why the function call does not match. Please help.

Variabels in elixir are lower case. You have Result in the second argument of do_rna/2. That is an atom in Elixir. — Justin Wood

Dogbert Dogbert · Accepted Answer · 2018-04-03T15:08:21

You probably meant to write result instead of Result in do_rna. An identifier starting with a capital letter is an atom in Elixir. With Result, that clause will only match if the second value is literally Result or :"Elixir.Result".

Why doesn't this functional call match in Elixir?

1 Answers