Defines a quasi-quoter for writing patterns that match the bodies of
multi-bindings. Uses the haskell-src-exts parser.
[nuP| P ] defines a
pattern that will match a multi-binding whose body matches
variables matched by
P will remain inside the binding; thus, for example,
in the pattern
[nuP| x |],
x matches the entire multi-binding.
case (nu Left) of [nuP| Left x |] -> x == nu id
- clP| P |
- does the same for the Cl type, and [clNuP| P |] works for both simultaneously: Cl (Mb ctx a).