When using the pattern (-> a b), both a and b were bound to the same type! The cause was using list comprehension instead of parallel list comprehension ([(x,y) | x <- ..., y <- ...] instead of [(x,y) | x <- ... | y <- ...]), thus resulting in the list [(x1,y1), (x1,y2), (x2,y1), (x2,y2)] instead of [(x1,y1), (x2,y2)].
david-christiansen
commented
2 years ago
When using the pattern
(-> a b), bothaandbwere bound to the same type! The cause was using list comprehension instead of parallel list comprehension ([(x,y) | x <- ..., y <- ...]instead of[(x,y) | x <- ... | y <- ...]), thus resulting in the list[(x1,y1), (x1,y2), (x2,y1), (x2,y2)]instead of[(x1,y1), (x2,y2)].