CODEWITHSUNDEEP
elixirphoenix-framework
tmp dev
tmp dev

Reputation: 9193

elixir function taking a parameter with do

I'm trying to wrap my head around Elixir and am confused about the following

def fun_myfunc(clause, do: expression) do

Specifically I'm a bit confused about the do: expression part. Is this a parameter being passed into the function, and also why is there a :. Is do a keyword in this context ?

This also gives rise to the following, question on Phoenix. If I look at the pipeline function https://hexdocs.pm/phoenix/Phoenix.Router.html#pipeline/2 I see the following signature pipeline(plug, list). What is list in this context and how do I infer it by looking at the documentation. I know that they have given examples where list looks like a bunch of expressions, but how do I gather that just by looking at the documentaion.

Upvotes: 1

Views: 140

Answers (1)

Adam Millerchip
Adam Millerchip

Reputation: 23091

do: expression is a keyword list. This is syntax sugar in two forms:

  • As the last parameter to a function, you can omit the surrounding []
  • As a keyword list, you can write key: value instead of the equivalent {:key, :value}

Both of these are documented in the above link.

The function is equivalent to:

def fun_myfunc(clause, [{:do, expression}]) do

The :do is simply an atom. It's up to the fun_myfunc to decide how to handle it.

I suspect you are actually looking at a macro defined with defmacro and misquoted it in your question. This is also how the if macro works, for example.

if foo do bar else baz is equivalent to if(foo, do: bar, else: baz), which is equivalent to if(foo, [{:do, bar}, {:else, baz}]).

As for the Phoenix part, that should be a separate question.

Upvotes: 1

Related Questions