Question

我的程序在元组列表中搜索</ strong>我将其写为以下

import List data BookInfo = Book Int String [String] deriving(Show) enter :: Int->String->[String]->BookInfo enter id name subject=Book id name subject bookId (Book id _ _ ) = id index :: BookInfo -> Int index (Book id name subject) = bookId (Book id name subject) arrayentering ::BookInfo->[BookInfo]->[BookInfo] arrayentering (Book id name subject) [] =[(Book id name subject)] arrayentering (Book _ " " [" "]) [] =[] arrayentering (Book id name subject) [(Book it namr suject)]= (Book id name subject):[(Book it name suject)] toList::[BookInfo]->[Int] toList [(Book id name subject) ]= map index [ (Book id name subject)] bubbleSort::(Ord t) => [t]->[t] bubbleSort[x,y,z,xs]= if x<y then x : [y,z,xs] else y : [x,z,xs] superBubble::(Ord t) => [[t]]->[[t]] superBubble a=map bubbleSort a combining::[BookInfo]->[[Int]] combining [(Book id name subject)]=superBubble [toList [(Book id name subject)]]

并从任何语法错误中清除它但在我尝试输入到combining()的元组列表后，它会给我发送运行时错误说

Exception:Not Exhaustive pattern in function Main.combining

这是什么意思？

请给我指示。如果可能的话，我想自己解决这个问题。

Answer 1

函数定义中的模式

combining [(Book id name subject)]=superBubble [toList [(Book id name subject)]]

仅匹配具有一个元素的列表。您在bubbleSort中遇到了类似的问题，其中

bubbleSort[x,y,z,xs]=

仅匹配具有四个元素和其他地方的列表。

我还没弄明白你打算如何工作，也许是使用变量模式（匹配所有参数）

combining books = superBubble (toList books)

适合吗？

我怀疑

arrayentering ::BookInfo->[BookInfo]->[BookInfo]
arrayentering (Book id name subject) [] =[(Book id name subject)]
arrayentering (Book  _  "     " ["    "]) [] =[]
arrayentering (Book id name subject) [(Book it namr suject)]=                         
              (Book id name subject):[(Book it name suject)]

应该是

arrayentering book bookList
    | empty book = bookList
    | otherwise  = book : bookList
      where
        empty (Book _ name subject) = all isSpace name && all (all isSpace) subject

（empty可能有误）。

toList应该只是map index。

Haskell中的运行时错误

1 个答案: