Check if the list is ascending (Haskell) -


i writing function check if tree if bst. i've tried print tree in in-order traversal list , check if list increasing. having error:

couldn't match expected type `a' against inferred type `[t]'   `a' rigid type variable bound       type signature `checklist' @ bst.hs:24:18 in pattern: x : y : xs in pattern: [x : y : xs] in definition of `checklist':     checklist [x : y : xs] = x <= y && checklist (y : xs)

here have far (only checklist function).

checklist :: (ord a) => [a] -> bool checklist [] = true checklist [x] = true checklist [x:y:xs] = x <= y && checklist (y:xs)

you want:

checklist :: (ord a) => [a] -> bool checklist [] = true checklist [x] = true checklist (x:y:xs) = x <= y && checklist (y:xs)

when tried use [ ] in final pattern, saying "match against list contains x:y:xs (also list!) sole element". doesn't match type [a].


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