Can I concatenate strings in Elixir and use the pipe operator?

Question

In Elixir, you can concatenate strings with the <> operator, like in "Hello" <> " " <> "World".

You can also use the pipe operator |> to chain functions together.

I'm trying to write the Elixir code to format the currency for an online game.

def format_price(price) do
  price/10000
  |> Float.round(2)
  |> to_string
  |> <> "g"
end

The above results in a syntax error. Am I overlooking a basic function that can concatenate strings? I know I can define one myself, but that seems like creating unnecessary clutter in my code if I can avoid it.

I realize I can accomplish the same thing, by simply chaining the methods together like to_string(Float.round(price/10000, 2)) <> "g", but this syntax isn't as nice to read, and it makes it more difficult to extend the method in the future, if I want to add steps in between.

Does Elixir have ways to concatenate text using the pipe operator, or is that not possible without defining the method yourself?

FWIW, I find the way you don't like ( nested functions ) more comprehensible than your '|>' version. — Fred the Magic Wonder Dog
– Fred the Magic Wonder Dog, Commented Dec 5, 2016 at 20:27

Dogbert · Accepted Answer · 2016-07-25 04:38:34Z

58

Yes, you can, by passing the full path to the function, which in this case is Kernel.<>:

iex(1)> "foo" |> Kernel.<>("bar")
"foobar"

answered Jul 25, 2016 at 4:38

Dogbert

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2 Comments

Kevin Over a year ago

Thanks - it really threw me off that there's no String.concat method in the same way that there's an Enum.concat method. I didn't realize that you could call the Kernel methods by just including the full path to the function.

Behnam Moh Jan 15 at 22:05

@Kevin You can call kernel methods like this because everything in Elixir is macros all the way down, like: a |> foo() |> def, do a |> Kernel.*(2).

ryanwinchester · Accepted Answer · 2021-07-09 18:20:32Z

My two cents

I realize I can accomplish the same thing, by simply chaining the methods together like to_string(Float.round(price/10000, 2)) <> "g", but this syntax isn't as nice to read, and it makes it more difficult to extend the method in the future, if I want to add steps in between.

You could use interpolation instead of concatenation. For example, you could do it like this and it's still okay to read, and simple, so easy to modify:

def format_price(price) do
  price = (price / 10000) |> Float.round(2)
  "#{price}g"
end

Answering your question

To answer your question:

Does Elixir have ways to concatenate text using the pipe operator, or is that not possible without defining the method yourself?

As mentioned in the other answer by @Dogbert, you can use Kernel.<>/2

Another solution is to use then/2.

def format_price(price) do
  (price / 10000)
  |> Float.round(2)
  |> to_string()
  |> then(&"#{&1}g")
end

or

def format_price(price) do
  (price / 10000)
  |> Float.round(2)
  |> to_string()
  |> then(&(&1 <> "g"))
end

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