symbol : String -> Parser ()

Parse symbols like ( and ,. page

The symbol function has type String -> Parser (). This means it must take in a String argument, and it will definitely return an Parser () value.

Note: This is good for stuff like Brackets and semicolons, but it probably should not be used for binary operators like + and - because you can find yourself in weird situations. For example, is 3--4 a typo? Or is it 3 - -4? I have had better luck with chompWhile isSymbol and sorting out which operator it is afterwards.

The empty tuple () is called the Unit type in Elm.

What does () mean? faq : It is the empty tuple or Unit Type. It serves much like void, null, or None in other languages.

⇒ Unit type