defmodule LangUtil do
		@doc ~S"""
		For use in a pipeline like so:

			{s, &Kernel.<>/2}
				|> oper_if(c.section,          "Section: #{c.section}\n")
				|> oper_if(true,               "Description: #{c.short_description}\n")
				|> oper_if(c.long_description, prefix_every_line(c.long_description, " ") <> "\n")
				|> elem(0)

		`expression` is not evaluated unless evaluation of `clause` is truthy.  This avoids
		blowing up on nils and other unexpected values.
		"""
		defmacro oper_if(state, clause, expression) do
			quote do
				{acc, operator} = unquote(state)
				result = if unquote(clause) do
					operator.(acc, unquote(expression))
				else
					acc
				end
				{result, operator}
			end
		end
	end