Why use null function instead of == [] to check for empty list in Haskell?

You should use null. In most cases it doesn’t matter, but it is a good habit to get into anyway, because occasionally you may want to check if a list of non-comparable things is empty. Here is a short, crisp example showing this difference:

> null [id]
False
> [id] == []
<interactive>:1:1: error:
    • No instance for (Eq (a0 -> a0)) arising from a use of ‘==’
        (maybe you haven't applied a function to enough arguments?)
    • In the expression: [id] == []
      In an equation for ‘it’: it = [id] == []