Why can't I chain String.replace?

Question

I'm working on a price format function, which takes a float, and represent it properly.

ex. 190.5, should be 190,50

This is what i came up with

  def format_price(price) do     price     |> to_string     |> String.replace ".", ","     |> String.replace ~r/,(\d)$/, ",\\1 0"     |> String.replace " ", ""   end 

If i run the following.

format_price(299.0) # -> 299,0 

It looks like it only ran through the first replace. Now if i change this to the following.

  def format_price(price) do     formatted = price     |> to_string     |> String.replace ".", ","      formatted = formatted     |> String.replace ~r/,(\d)$/, ",\\1 0"      formatted = formatted     |> String.replace " ", ""   end 

Then everything seems to work just fine.

format_price(299.0) # -> 299,00 

Why is this?

Answer 1

EDIT On the master branch of Elixir, the compiler will warn if a function is piped into without parentheses if there are arguments.

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This is an issue of precedence that can be fixed with explicit brackets:

price |> to_string |> String.replace(".", ",") |> String.replace(~r/,(\d)$/, ",\\1 0") |> String.replace(" ", "") 

Because function calls have a higher precedence than the |> operator your code is the same as:

price |> to_string |> String.replace(".",   ("," |> String.replace ~r/,(\d)$/,     (",\\1 0" |> String.replace " ", ""))) 

Which if we substitute the last clause:

price |> to_string |> String.replace(".",   ("," |> String.replace ~r/,(\d)$/, ".\\10")) 

And again:

price |> to_string |> String.replace(".", ",") 

Should explain why you get that result.