Thank you for your response. When trying to use ?as follows:
def to_rna(dna) do
Enum.map_join(dna, &convert(&1))
end
defp convert(?G) do
'C'
end
the test:
assert RNATranscription.to_rna('G') == 'C'
fails with:
Assertion with == failed
code: assert RNATranscription.to_rna('G') == 'C'
left: "C"
right: 'C'
stacktrace:
I think it’s because of Enum.map_join joiner 
map_join(enumerable, joiner \\ "", mapper) View Source
map_join(t(), String.t(), (element() -> String.Chars.t())) :: String.t()
i.e. it returns a String.t(), you’re looking for charlist() (or [char()]).
map(enumerable, fun) View Source
map(t(), (element() -> any())) :: list()
returns list() or [any()] or more accurately a list of the type returned by the mapping function, e.g.:
map([char()], (char() -> char())) :: [char()]
something like
map([typeA()], (typeA() -> typeB())) :: [typeB()]
It’s just that Enumerable.t() is anything that has an implementation of the Enumerable protocol (which list() does).
charlist() is literally a list of character valued integersString.t() is a binary(), a contiguous chunk of memory where each byte is a UTF-8 codepoint.
Is it one of the solutions would as follows or there are other Enum, String, Enumerable, etc. hiddent functions ?
def to_rna(dna) do
Enum.map(dna, &convert(&1))
end
defp convert(?G) do
?C
end
test "transcribes guanine to cytosine" do
assert RNATranscription.to_rna('G') == 'C'
end
By the way, where does it come from, this ? sign, - I find it nowhere in official guides.
The complete module:
@spec to_rna([char]) :: [char]
def to_rna(dna) do
Enum.map(dna, &convert(&1))
end
defp convert(?G) do
?C
end
defp convert(?C) do
?G
end
defp convert(?T) do
?A
end
defp convert(?A) do
?U
end
defp convert(letter) do
IO.puts(:stderr, "Couldn't find matching for #{letter}")
letter
end
In Elixir, you can get a character’s code point by using
?
There are a couple of ways to retrieve a character integer codepoint. One may use the
?construct:
or there are other Enum, String, Enumerable, etc. hidden functions ?
I’m not sure what you are asking …
I asked because it looked a little bit weird for me to compare two characters by using ? sign instead of === or == or just equals that exist in other languages. More of that, I also have to return the character to replace with using the same ? sign.
? simply generates the integer (codepoints) that is equivalent to the character, which in the case of ASCII will fit into 8 bits. What you call a comparison is actually a pattern match.
defp convert(letter) do
case letter do
?G ->
?C
?C ->
?U
?T ->
?A
?A ->
?U
_ ->
IO.puts(:stderr, "Couldn't find matching for #{letter}")
letter
end
end