4 ms·

Great article, thanks! I'm not an expert Alchemist by any means, but whenever I see a `cond`, I try to see if it can be refactored out using pattern matching (

Great article, thanks! I'm not an expert Alchemist by any means, but whenever I see a `cond`, I try to see if it can be refactored out using pattern matching (after I was picked up on the same thing during an interview!) defp formatted_hour("AM", "12"), do: "00" defp formatted_hour("AM", hours), do: hours defp formatted_hour("PM", "12"), do: "12" defp formatted_hour("PM", hours), do: 12 + String.to_integer(hours)

Alacart 9y ago
Pattern matching is awesome and we should make use of it whenever appropriate, but not every situation is appropriate. For instance, if your formatted_hour functions were larger, or shared some amount of code between them, then cond might be a great option instead. Or case, or even the dreaded if statement. As a community, sometimes we overuse our cool special features just because we have them! Personally, I like the case statement as a middle ground for lots of scenarios. You still get pattern matching and it's pretty readable.
- midgetjones 9y ago
  If the formatted_hour functions were larger or shared some amount of code, I wouldn't have suggested it ;)
ericdouglas 9y ago
Awesome! Many thanks for the tip. I'll refactor the code :)
ulucs 9y ago
I personally like recursive pattern matching defp formatted_hour("AM", hours), do: rem(hours, 12) defp formatted_hour("PM", hours), do: 12 + formatted_hour("AM", hours)
- midgetjones 9y ago
  Nice!
hokiewv 9y ago
I agree though one thing I would caution is it is good practice to always return the same type from a function even though it is an untyped language. The whole thing can be boiled down even more if pattern matching is used in parsing the initial string. def convert(<<h::bytes-size(2)>> <> ":" <> <<m::bytes-size(2)>> <> ":" <> <<s::bytes-size(2)>> <> <<period::bytes-size(2)>>) do "#{formatted_hour(h,period)}:#{m}:#{s}" end defp formatted_hour(hours,"PM"), do: "#{String.to_integer(hours) + 12}" defp formatted_hour("12","AM"), do: "00" defp formatted_hour(hours, "AM"), do: hours
- midgetjones 9y ago
  Good point! If you're going to pattern match in the initial string then who even needs the second function? def convert("12:" <> <<m::bytes-size(2)>> <> ":" <> <<s::bytes-size(2)>> <> "AM") do "00:#{m}:#{s}" end def convert(<<h::bytes-size(2)>> <> ":" <> <<m::bytes-size(2)>> <> ":" <> <<s::bytes-size(2)>> <> "PM") do h = 12 + String.to_integer(h) "#{h}:#{m}:#{s}" end def convert(<<h::bytes-size(2)>> <> ":" <> <<m::bytes-size(2)>> <> ":" <> <<s::bytes-size(2)>> <> "AM") do "#{h}:#{m}:#{s}" end Whether that's an improvement or not is another matter :)
  - ericdouglas 9y ago
    Crazy stuff! :D I'm wondering how our future-self would feel about such cleverness haha
- ericdouglas 9y ago
  I really liked this: "#{String.to_integer(hours) + 12}" Used it now refactoring the code, many thanks for your suggestion!

Alacart 9y ago

Pattern matching is awesome and we should make use of it whenever appropriate, but not every situation is appropriate. For instance, if your formatted_hour functions were larger, or shared some amount of code between them, then cond might be a great option instead. Or case, or even the dreaded if statement. As a community, sometimes we overuse our cool special features just because we have them! Personally, I like the case statement as a middle ground for lots of scenarios. You still get pattern matching and it's pretty readable.

midgetjones 9y ago
If the formatted_hour functions were larger or shared some amount of code, I wouldn't have suggested it ;)

ericdouglas 9y ago

Awesome! Many thanks for the tip. I'll refactor the code :)

ulucs 9y ago

I personally like recursive pattern matching defp formatted_hour("AM", hours), do: rem(hours, 12) defp formatted_hour("PM", hours), do: 12 + formatted_hour("AM", hours)

midgetjones 9y ago
Nice!

hokiewv 9y ago

I agree though one thing I would caution is it is good practice to always return the same type from a function even though it is an untyped language. The whole thing can be boiled down even more if pattern matching is used in parsing the initial string. def convert(<<h::bytes-size(2)>> <> ":" <> <<m::bytes-size(2)>> <> ":" <> <<s::bytes-size(2)>> <> <<period::bytes-size(2)>>) do "#{formatted_hour(h,period)}:#{m}:#{s}" end defp formatted_hour(hours,"PM"), do: "#{String.to_integer(hours) + 12}" defp formatted_hour("12","AM"), do: "00" defp formatted_hour(hours, "AM"), do: hours

midgetjones 9y ago
Good point! If you're going to pattern match in the initial string then who even needs the second function? def convert("12:" <> <<m::bytes-size(2)>> <> ":" <> <<s::bytes-size(2)>> <> "AM") do "00:#{m}:#{s}" end def convert(<<h::bytes-size(2)>> <> ":" <> <<m::bytes-size(2)>> <> ":" <> <<s::bytes-size(2)>> <> "PM") do h = 12 + String.to_integer(h) "#{h}:#{m}:#{s}" end def convert(<<h::bytes-size(2)>> <> ":" <> <<m::bytes-size(2)>> <> ":" <> <<s::bytes-size(2)>> <> "AM") do "#{h}:#{m}:#{s}" end Whether that's an improvement or not is another matter :)
- ericdouglas 9y ago
  Crazy stuff! :D I'm wondering how our future-self would feel about such cleverness haha
ericdouglas 9y ago
I really liked this: "#{String.to_integer(hours) + 12}" Used it now refactoring the code, many thanks for your suggestion!