Haskell中的「輸入解析錯誤」if-then-else有條件的

Question

當我試圖編譯它時，下面的do塊會拋出錯誤「輸入conn'解析錯誤」。我已經嘗試了許多不同的if-then-else語句的配置，無濟於事。數據庫邏輯在我添加條件之前就工作了，所以這沒有問題。我在其他線路上有太多線路嗎？有沒有什麼辦法可以解決這個問題，而不需要完全修改邏輯？

main = do 
    contents <- BL.getContents 
    let myData = decode contents :: Maybe Data 
    if maybe True (\x -> result x /= "success") myData 
     then error ("JSON download failed") 
     else let myTrades = process myData 
     conn <- connectSqlite3 "trades.db" 
     insert <- DB.prepare conn "INSERT INTO trades VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?);" 
     DB.executeMany insert $ map (\xs -> map DB.toSql xs) myTrades 
     DB.commit conn 
     DB.disconnect conn 

Answer 1

您需要else像這樣以後引進do塊：

else do let myTrades = process myData 
      conn <- connectSqlite3 "trades.db" 
      insert <- DB.prepare conn "INSERT INTO trades VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?);" 
      DB.executeMany insert $ map (\xs -> map DB.toSql xs) myTrades 
      DB.commit conn 
      DB.disconnect conn