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- import Data.List (lookup)
- insert :: Eq a => (a,b) -> [(a,b)] -> [(a,b)]
- insert (a,b) [] = [(a,b)]
- insert (a,b) ((c,d):rest) = if a == c
- then (a,b) : rest
- else (c,d) : insert (a,b) rest
- dict :: [(String, String)]
- dict = [("", "")]
- main = do
- insert ("onekey", "onevalue") dict
- print dict
- print $ lookup "onekey" dict
- $ runghc rndict.hs
- rndict.hs:22:1: error:
- • Couldn't match expected type ‘IO t0’ with actual type ‘[()]’
- • In the expression: main
- When checking the type of the IO action ‘main’
- rndict.hs:24:9: error:
- • Couldn't match type ‘IO’ with ‘[]’
- Expected type: [()]
- Actual type: IO ()
- • In a stmt of a 'do' block: print dict
- In the expression:
- do { insert ("onekey", "onevalue") dict;
- print dict;
- print $ lookup "onekey" dict }
- In an equation for ‘main’:
- main
- = do { insert ("onekey", "onevalue") dict;
- print dict;
- print $ lookup "onekey" dict }
- rndict.hs:25:9: error:
- • Couldn't match type ‘IO’ with ‘[]’
- Expected type: [()]
- Actual type: IO ()
- • In a stmt of a 'do' block: print $ lookup "onekey" dict
- In the expression:
- do { insert ("onekey", "onevalue") dict;
- print dict;
- print $ lookup "onekey" dict }
- In an equation for ‘main’:
- main
- = do { insert ("onekey", "onevalue") dict;
- print dict;
- print $ lookup "onekey" dict }
- import Data.List (lookup)
- insert :: Eq a => (a,b) -> [(a,b)] -> [(a,b)]
- insert (a,b) [] = [(a,b)]
- insert (a,b) ((c,d):rest) = if a == c
- then (a,b) : rest
- else (c,d) : insert (a,b) rest
- dict :: [(String, String)]
- dict = [("", "")]
- main = do
- let d = insert ("onekey", "onevalue") dict
- print d
- print $ lookup "onekey" d
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