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| -rw-r--r-- | sem7/pp/lec5.hs | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/sem7/pp/lec5.hs b/sem7/pp/lec5.hs index 1b596f5..3340346 100644 --- a/sem7/pp/lec5.hs +++ b/sem7/pp/lec5.hs @@ -1,3 +1,4 @@ +import Data.Set (Set, empty, member, insert) -- Opgaver før lecture sum' x | x > 0 = x + sum' (x-1) @@ -46,3 +47,45 @@ cfrac x n = let intPart = truncate x in -- REMEMBER fromInteger for ***'s sake. -- Without it, x will be tagged with (RealFrac a, Integral a) => a, -- which destroys everything. + +-- Hmm it does not really work perfectly because of the rounding errors + + +-- Lets just create the last function instead. It must extract the last element of a list. +-- It's type is probably last :: [a] -> maybe a + +last' [] = Nothing +last' (x:[]) = Just x +last' (_:xs) = last' xs + +-- Flatten a two level deep list. +flatten' [] = [] +flatten' (x:xs) = x ++ flatten' xs + +-- Okay so we can with curtianty say that the function takes an array of something. +-- This is clear by the pattern matches. +-- However because we use ++ we also know that we return a list, as it's signature is [a] -> [a] -> [a]. +-- From this we can also infer that x must be a list. +-- The function type is therefore flatten' :: [[a]] -> [a] + +-- When running :t on flatten' we get the same. + + +valid :: (Integral a, Ord a) => [(a, b)] -> Bool +valid = recur empty + where recur _ [] = True + recur known (pair:rest) = + if key `member` known + then False + else recur (insert key known) rest + where key = fst pair + + +-- TODO, case where key is not in is unhandled +lookup' :: (Integral a, Ord a) => [(a, b)] -> a -> b +lookup' (pair:rest) key = if (fst pair) == key + then (snd pair) + else lookup' rest key + +-- I dont see how findfun and lookup are not the same +findfun = lookup' |