The Pug Automatic

The case for multiple anonymous function bodies

Written June 12, 2020. Tagged Elixir.

Here's a dollop of developer delight in Elixir.

Named functions can have multiple bodies, as you probably know:

def present_result(:ok), do: "Success!"
def present_result(:error), do: "Failure!"

It's perhaps less well known that the same applies to anonymous functions. You can use this to simplify situations where you'd otherwise use case.

For example, instead of:

Enum.each(results, fn (result) ->
case result do
:ok -> IO.puts "Success!"
:error -> IO.puts "Failure!"

You can do:

Enum.each(results, fn
:ok -> IO.puts "Success!"
:error -> IO.puts "Failure!"

And you can pattern match just like in any function definition, of course. I did something like this recently:

results = [
{:ok, "It worked"},
{:ok, "It also worked"},
{:error, "It fell on its face"},

counts = Enum.frequencies_by(results, fn {status, _count} -> status end)
# => [{:ok, 2}, {:error, 1}]

Enum.each(counts, fn
{:ok, 1} -> IO.puts "1 success!"
{:ok, count} -> IO.puts "#{count} successes!"
{:error, 1} -> IO.puts "1 failure!"
{:error, count} -> IO.puts "#{count} failures!"

Pretty nice!