import Data.List
    primes = Data.List.nubBy (\a b -> gcd a b > 1) [2..]
    findTwins primes = [(p,q) | (p:q:_) <- tails primes, q == p+2]
    main = mapM_ print . take 10 . findTwins $ primes

    findBigTwins gap primes = [(p,q) | (p:qs) <- tails primes, let q = p+gap, q `elem` takeWhile (<= q) qs]

The power of Egison's pattern matching becomes more obvious when we consider more general pattern such as (p, p+ 100) not only (p, p+2).

We can write the first 5 prime pairs whose form is (p, p+100) with a small modification for pattern matching for twin primes.

  (take 5
       (match-all primes (list integer)
         [<join _ <cons $p <join _ <cons ,(+ p 100) _>>>>
          [p (+ p 100)]]))
  ;=>{[3 103] [7 107] [13 113] [31 131] [37 137]}

Not only that, but you have redundancy between the ,(+ p n) part of the pattern and the emitted result of [p (+ p n)].

Point being: I applaud the attempt here, but it's not something I'll ever want to use.

Not if primes is a set.