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Comment by anonymousDan | Hacker News Reader

I wish that elixir had some syntax to simplify variable rebinding when returning from an if statement (as opposed to an if else). For example, some way to say leave the variable unchanged if the if statement is false instead of having to clutter up the program with one line else clauses.

Eg. myvar = 5 myvar = if somepredicate() do 200 end

Will currently assign None to myvar if somepredicate is false.

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There are a couple of options to simplify and emulate a ternary operator:

if x, do: y, else: z

Or, though it's not very idiomatic Elixir, this also works:

x && y || z

The binary matching is relatively idiomatic in liveview - check the CoreComponents files.

I prefer explicit readability. Alternatives I can think of are unappealing.

if you're writing Elixir code you'll find that most of the times the assignment is close to where you need the variable, so you usually end up writing something along the line of

   var = if x, do: 200, else: 5

myvar = 5

myvar = if somepredicate() do 200 else myvar end

The wish of the OP is to avoid writing "else myvar". You could write a macro I guess. Something like the one below. Not that I have named the macro cond_assign for conditional assignment but there is no real assignement in Elixir, it is the match operator. Here we restrict its usage to "assignment" so expr1 should be a variable.

  defmodule OurMacro do
    defmacro cond_assign(expr1, expr2, do: block) do
      quote do
        unquote(expr1) = if unquote(expr2), do: unquote(block), else: unquote(expr1)
      end
    end
  end

  iex> import OurMacro
  OurMacro
  iex> myvar = 5
  5
  iex> cond_assign myvar, false, do: 200
  5
  iex> myvar
  5
  iex> cond_assign myvar, true, do: 200
  200
  iex> myvar
  200

Here is a better version that checks if expr1 is a variable. The condition "is_atom(x)" might be too strong.

  defmodule OurMacro do
    defmacro cond_assign(expr1, expr2, do: block) do
      case expr1 do
        {x, _, y} when is_atom(x) and is_atom(y) -> nil
        _ -> :erlang.error(RuntimeError.exception("The lvalue is not a variable: #{Macro.to_string(expr1)}"))
      end
      quote do
        unquote(expr1) = if unquote(expr2), do: unquote(block), else: unquote(expr1)
      end
    end
  end

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