Question

我目前正在Haskell的（https://adventofcode.com/2018）进行adventofcode挑战，以更好地了解该语言。

我的问题是，当我尝试启动我的应用程序时，它只是在执行主要功能后挂起，没有任何错误。当我尝试在ghci内部执行函数时，似乎没有任何问题，当我尝试在calc函数内部传递一个List时，它也可以在main内部运行并输出结果。

import Data.Maybe                                                                                                                                                                              
import Control.Monad                                                                                                                                                                           

main :: IO()                                                                                                                                                                                   
main = do                                                                                                                                                                                      
    file <- readFile "./input.txt"                                                                                                                                                             
    let linesOfFile = lines file                                                                                                                                                               
    print $ calc (linesOfFile) (0, [])                                                                                                                                                         

calc :: [String] -> (Int, [Int]) -> Int                                                                                                                                                        
calc arr preState = let                                                                                                                                                                        
    state = foldl (flip nextStep) preState arr                                                                                                                                                 
    past = snd state                                                                                                                                                                           
    duplicate = repeated past                                                                                                                                                                  
    in if isJust duplicate                                                                                                                                                                     
        then fromJust duplicate                                                                                                                                                                
        else calc arr state                                                                                                                                                                    

nextStep :: String -> (Int, [Int]) -> (Int , [Int])                                                                                                                                            
nextStep str state                                                                                                                                                                             
    | head str == '-' = let newState = (fst state) - (read $ tail str :: Int)                                                                                                                  
                            pastStates = snd state                                                                                                                                             
                            in (newState, pastStates ++ [newState])                                                                                                                            
    | head str == '+' = let newState = (fst state) + (read $ tail str :: Int)                                                                                                                  
                            pastStates = snd state                                                                                                                                             
                            in (newState, pastStates ++ [newState])                                                                                                                            

repeated :: [Int] -> Maybe Int                                                                                                                                                                 
repeated xs = go xs []                                                                                                                                                                         
    where                                                                                                                                                                                      
        go [] _ = Nothing                                                                                                                                                                      
        go (x : xs) visited =                                                                                                                                                                  
            if x `elem` visited                                                                                                                                                                
                then Just x                                                                                                                                                                    
                else go xs (x : visited)

input.txt位于（{https://pastebin.com/7zhWBQr8）

和Github链接：https://github.com/mvorwieger/advent-of-code/tree/master/haskell/2

是没有解决办法吗？

Haskell程序卡在main中没有错误？

0 个答案: