Desugared:
{- plain CoRec -}
Main.foldPair ::
    for all a, b. (a -> a -> a, b -> b -> b) -> (a, b) -> [(a, b)] -> (a, b)
Main.foldPair =
    /\ a b -> \ fg.122 ab.123 ds.124 ->
	let
	  fail.125 =
	      (error (a, b))
		  "\"ds031.hs\", line 4: pattern-matching failure [function binding]\n"S in
	let
	  fail.141 =
	      case fg.122 of {
		MkTuple2 f.126 g.127 ->
		    case ds.124 of {
		      (:) ds.128 abs.129 ->
			  case ds.128 of {
			    MkTuple2 a.130 b.131 ->
				let ab.132 = ab.123 in
				let fg.133 = fg.122 in
				let
				  ds.134 =
				      ((Main.foldPair a) b)
					  fg.133 ab.132 abs.129 in
				let
				  u.137 =
				      case ds.134 of {
					MkTuple2 u.135 v.136 -> u.135
				      } in
				let
				  v.140 =
				      case ds.134 of {
					MkTuple2 u.138 v.139 -> v.139
				      }
				in 
				  MkTuple2!
				      a
				      b
				      (f.126 a.130 u.137)
				      (g.127 b.131 v.140)
			  }
		      _ ->  fail.125
		    }
	      }
	in 
	  case ds.124 of {
	    Nil -> ab.123
	    _ ->  fail.141
	  }
{- end plain CoRec -}