Characters are just integers, use it:

def digit_value(d) when d in $0..$9, do: d - $0
def digit_value(d) when d in $a..$z, do: d - $a + 10
def digit_value(d) when d in $A..$Z, do: d - $A + 36

Or you could even metaprogramming roughly like this: (untested)

Enum.concat([$0..$9, $a..$z, $A..$Z])
|> Enum.with_index()
|> Enum.each(fn {d, i} ->
  def digit_value(unquote(d)), do: unquote(i)
end)

There are a lot solutions that are nicer than your module attribute and still benefit from compiletime optimisations.

PS: function calls are (usually) faster than map-lookups.

First of all:

data = Enum.to_list(?0..?9) ++ Enum.to_list(?a..?z)

result = Enum.reduce(data, %{digits: %{}, symbols: %{}}, fn integer, acc ->
  letter = <<integer::utf8>>
  acc |> put_in([:digits, letter], integer) |> put_in([:symbols, integer], letter)
end)

@digits result.digits
@symbols result.symbols

With this you are iterating data only once and don’t have so huge badly formatted map.

Look that Map.to_list/1 is one iteration, Enum.map/2 is second and Map.new/1 is third.

Secondly:

@digits Map.to_list(@symbols) |> Enum.map(fn {k, v} -> {v, k} end) |> Map.new()
# better
@digits @symbols |> Map.to_list() |> Enum.map(fn {k, v} -> {v, k} end) |> Map.new()

Finally:

unless num < base do
  from_decimal(div(num, base), base, result)
else
  result
end
# better
if num < base do
  result
else
  num |> div(base) |> from_decimal(base, result)
end

I also recommend to take a look at Erlang source if C is not a problem for you.

You can start from: erts/emulator/beam/big.c:325 (in 22.0-rc.1 release). You can find there source of integer_to_binary/3 in which you can find more inspiration for further speed improvements.

Here is helpful resource:

in which I’m linking some style guides:

oops, I did not properly read your code, sorry …
Let me correct that:

data = Enum.to_list(?0..?9) ++ Enum.to_list(?a..?z) ++ Enum.to_list(?A..?Z)
data_with_indexes = Enum.with_index(data)

result = Enum.reduce(data_with_indexes, %{digits: %{}, symbols: %{}}, fn {integer, index}, acc ->
  letter = <<integer::utf8>>
  acc |> put_in([:digits, letter], index) |> put_in([:symbols, index], letter)
end)

Look how simple is change in my code example - it’s always big priority for me. Most configurable and generic solutions are best, because they are easy to change and therefore even with small mistake it’s pretty simply to correct that. Look that I only added one more range and indexes here - most important part of code is not really changed.

Well … remember that every language is designed for its own purposes. Similarly let’s keep kawaii thing in manga/anime.

But seriously … while you can have your own opinions styles guides (especially this one which follows Elixir core group) are really good and allows to keep code easy to read. Think that you read your code after (let’s say) year and look that you would probably not remember it well. If that happens having heavy readable code even for your own private projects it’s extremely important rule in my opinion.

yeah, I remember that I was correcting that, but I have checked wrong option (synchronize of selected text with clipboard) in my Plasma 5 clipboard app, so it changed corrected text in clipboard with selected (to replace) text.

As said it’s just a good source of inspiration i.e. sometimes you just need to stop work on your code and take a look how similar things were solved by others. I believe that there are some optimization things that simplest implementation does not have. Erlang as well as Elixir is maintained by really experienced people. For learning purposes it’s almost like cheating having such a good open source resources and such a waste to don’t take a look on them at least once.

P.S.
No matter what you see - conspiracy theory which says that I’m never sleeping is definitely not true.