[Haskell-cafe] Very binding semicolon

From the department of improbable syntax/I don't get how this works, but it does:

f :: [a] -> [a] ;; f xs = xs ++ reverse xs

Nicely (to my eye) groups/indents the binding under the signature. Especially handy with ScopedTypeVariables, to show how the scoped vars 'belong'

f :: forall a. [a] -> [a] ;; f xs = xs ++ ys where ys :: [a] ys = reverse xs

The doubled `;;` stands out like a ditto. It could be a single semicolon (which means there's an empty decl/binding between the semis -- I don't see that's allowed by the syntax). Unfortunately, for multi-line bindings you need to repeat the `;;`

f :: [a] -> [a] ;; f [] = [] ;; f xs = xs ++ reverse xs