6. Elixir: Function Clauses

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HTTP Request in Elixir

Request Example

Here’s the request we pasted in the video:

request = """
GET /bears HTTP/1.1
Host: example.com
User-Agent: ExampleBrowser/1.0
Accept: */*
 
"""

There’s Another Way!

If you’ve played around with Elixir before this course, then you might be thinking: “Hey, there’s another way to do this!” And you’d be right! Instead of passing three arguments to the route function clauses, you can pass just the conv map and pattern match on it, like so:

def route(%{method: "GET", path: "/wildthings"} = conv) do
  %{ conv | resp_body: "Bears, Lions, Tigers" }
end
 
def route(%{method: "GET", path: "/bears"} = conv) do
  %{ conv | resp_body: "Teddy, Smokey, Paddington" }
end

If, however, you’re new to Elixir, we haven’t yet learned how to pattern match maps in this course. Hang with us! We’ll explore this technique in depth starting in Module 8.

Parentheses

When calling a function with arguments, parentheses are optional as long as their absence does not introduce ambiguity.

For example, in the video we used parentheses when calling the route/3 function which takes three arguments:

route(conv, conv.method, conv.path)

If you prefer, you can remove the parentheses:

route conv, conv.method, conv.path

There’s no ambiguity there.

Parentheses with Piping

However, parentheses are required when piping into a function call. For example, you’ll get a warning about the following code being ambiguous:

[method, path, _] =
  request
  |> String.split "\n"
  |> List.first
  |> String.split " "

Using parentheses makes it unambiguous:

[method, path, _] =
  request
  |> String.split("\n")
  |> List.first()
  |> String.split(" ")

Our general rule is to use parentheses when calling functions to avoid any ambiguity. However, sometimes we’re inconsistent. For example, when calling IO.puts it just feels more natural to omit the parentheses.

Code So Far

The code for this section is in the appropriate function-clauses directory found within the video-code directory of the code bundle

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