[1 of 1] Compiling Main ( prog.hs, prog.o )
prog.hs:8:23:
Couldn't match expected type `Maybe (c0, a0)'
with actual type `(c1, c'0)'
Expected type: a0 -> Maybe (c0, a0)
Actual type: a0 -> (c1, c'0)
In the first argument of `unfoldr', namely
`(id
&&&
\ x
-> x `div` 2 <$ guard (even x) <|> x * 3 + 1 <$ guard (x /= 1))'
In the second argument of `(.)', namely
`unfoldr
(id
&&&
\ x
-> x `div` 2 <$ guard (even x) <|> x * 3 + 1 <$ guard (x /= 1))'