模式匹配可变大小的Haskell列表 [英] Pattern Matching a Haskell list of variable size

问题描述

编辑：当这个累了的时候，我不应该编码。我正在编译与运行时不同的程序副本。

我有以下代码可以在我的程序启动时使单个参数成为可选项。

  main = do 
 args<  -  getArgs 
 handleArgs args 
 
 handleArgs :: [String]  - > IO（）
 handleArgs（server：nick：channel：[]）= IRC.startIRC server 6667 nick channel 
 handleArgs（server：port：nick：channel：[]）= IRC.startIRC server port :: Int）nick channel 
 handleArgs _ = putStrLn给出的参数不正确。 
  

如果我像 ./程序运行它irc.freenode.net 6667 somenick #somechannel ，它运行。但是，如果我像 ./ program irc.freenode.net somenick #somechannel 运行它，这应该使args成为irc.freenode列表。 net：somenick：＃somechannel：[] 如果我理解正确，
会给出一个模式匹配错误，指向 args< - getArgs 行，当我尝试用ghc编译后运行它时。

更准确地说，错误是：
<$ c $

解决方案 / div>

检查你的shell是否以＃开头的部分作为注释来解释，例如（shopt）上的 interactive_comments 。 #somechannel 可能会被解释为注释。

EDIT: I shouldn't be coding when this tired. I was compiling a different copy of the program than I was running. Sorry for wasting your time.

I have the following code to make a single argument optional in my program's startup.

main = do
    args <- getArgs
    handleArgs args

handleArgs :: [String] -> IO ()
handleArgs (server:nick:channel:[]) = IRC.startIRC server 6667 nick channel
handleArgs (server:port:nick:channel:[]) = IRC.startIRC server (read port :: Int) nick    channel
handleArgs _ = putStrLn "Incorrect arguments given."

If I run it like ./program irc.freenode.net 6667 somenick #somechannel, it runs. However, if I run it like ./program irc.freenode.net somenick #somechannel, which should make args be a list "irc.freenode.net":"somenick":"#somechannel":[] if I understand it correctly, it gives a pattern match error pointing to the args <- getArgs line when I try to run it after compiling with ghc.

More precisely, the error is: mbot: user error (Pattern match failure in do expression at core.hs:9:4-32)

解决方案

Check that your shell is not interpreting the part starting with # as a comment, e.g. bash with interactive_comments on (shopt). #somechannel may be interpreted as a comment.

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