Pattern match using smart constructor

Question

Is there a way to pattern match smart constructors, outside of its module?

Something like this:

import MyModule (thing)

fn (thing 3) = True

without being able to write this:

fn (Thing 3) = True

where thing is a smart constructor for Thing.

Answer 1

Define this in MyModule and export it:

extract :: Thing -> Int
extract (Thing x) = x

Use the view patterns extension:

{-# LANGUAGE ViewPatterns #-}

fn :: Thing -> Bool
fn (extract -> 3) = True