protein_translation.exs

defmodule ProteinTranslation do
  @codons %{
    "UGU" => "Cysteine",
    "UGC" => "Cysteine",
    "UUA" => "Leucine",
    "UUG" => "Leucine",
    "AUG" => "Methionine",
    "UUU" => "Phenylalanine",
    "UUC" => "Phenylalanine",
    "UCU" => "Serine",
    "UCC" => "Serine",
    "UCA" => "Serine",
    "UCG" => "Serine",
    "UGG" => "Tryptophan",
    "UAU" => "Tyrosine",
    "UAC" => "Tyrosine",
    "UAA" => "STOP",
    "UAG" => "STOP",
    "UGA" => "STOP"
  }
  @invalid_codon "invalid codon"
  @invalid_rna "invalid RNA"

  @doc """
  Given an RNA string, return a list of proteins specified by codons, in order.
  """
  @spec of_rna(String.t()) :: {atom, list(String.t())}
  def of_rna(rna), do: of_rna(rna, [])

  defp of_rna("", []), do: { :error, @invalid_rna }
  defp of_rna("", proteins), do: { :ok, proteins }
  defp of_rna(<<codon::binary-size(3), tail::binary>>, proteins) do
    case of_codon(codon) do
      { :ok, "STOP" } -> of_rna("", proteins)
      { :ok, protein } -> of_rna(tail, proteins ++ [protein])
      { :error, _ } -> of_rna("", [])
    end
  end

  @doc """
  Given a codon, return the corresponding protein

  UGU -> Cysteine
  UGC -> Cysteine
  UUA -> Leucine
  UUG -> Leucine
  AUG -> Methionine
  UUU -> Phenylalanine
  UUC -> Phenylalanine
  UCU -> Serine
  UCC -> Serine
  UCA -> Serine
  UCG -> Serine
  UGG -> Tryptophan
  UAU -> Tyrosine
  UAC -> Tyrosine
  UAA -> STOP
  UAG -> STOP
  UGA -> STOP
  """
  @spec of_codon(String.t()) :: {atom, String.t()}
  def of_codon(codon) do
    case @codons[codon] do
      nil -> { :error, @invalid_codon }
      protein -> { :ok, protein }
    end
  end
end