Well, when you use Emacs, every key is a λ key...

When you use haskell-mode in Emacs, \ renders as λ. (And only when you're using it as a lambda. '\n' still renders as '\n', not 'λn'.)

I assume the λ is just a placeholder for any character.

In vim I used digraph.

<C-k>l*

You can have the complete list with :dig