这里有任何Haskellers吗？ [英] Any Haskellers here ?

问题描述

大家好，只是将我的脚趾浸入Haskell的水域并需要一些帮助解析命令行args（是的，我已经google了）下面的代码完美无缺，但我想在命令行上传递一个值 - 有一个名为getArgs的Haskell函数，它返回所有命令行参数的字符串列表，但我无法弄清楚如何从列表中检索一个int - 我说的是查询3400我想说（如在C中）查询atoi（ arg [1]） - 任何Haskellers在那里？

Hi all, just dipping my toes into the waters of Haskell and need some help parsing command line args ( yes I've googled ) the code below works perfectly but I would like to pass a value on the command line - there is a Haskell function called getArgs that returns a string list of all command line params but I can't work out how to retrieve an int from the list - where I say do query 3400 I would like to say ( as in C ) query atoi(arg[1]) - any Haskellers out there ?

import Database.HDBC.Sqlite3
import Database.HDBC
import System.Environment

main :: IO()
main =
     do query 3400


query :: Int -> IO ()
query id =
    do conn <- connectSqlite3 "library.db"
       r <- quickQuery' conn
            "SELECT id, name from contributors where id = ? ORDER BY id" [toSql id]

       -- Convert each row into a String
       let stringRows = map convRow r

       -- Print the rows out
       mapM_ putStrLn stringRows

       -- And disconnect from the database
       disconnect conn

    where convRow :: [SqlValue] -> String
          convRow [sqlid, sqlname] =
              show id ++ ": " ++ name
              where id = (fromSql sqlid)::Integer
                    name = case fromSql sqlname of
                             Just x -> x
                             Nothing -> "NULL"
          convRow x = fail $ "Unexpected result: " ++ show x

推荐答案

意外结果： ++ show x

"Unexpected result: " ++ show x

我在Haskell生锈，但是，我想

I am rusty at Haskell, however, I suppose

main = do
  args <- getArgs
  query  (read (args!!1) :: Int)

应该可以解决问题。

should do the trick.

我当时即将发布这似乎有用的

I was just about to post this which seems to work

arg1 <- getArgs
 query (read

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