Question

我对haskell缩进感到非常困惑，特别是do阻止了let和where

我在行action <-＆＃34上遇到以下错误; do-block中的最后一个语句必须是表达式＆＃34;我该如何解决这个问题？

我有以下定义

type NeovimRead = Neovim r st Text
type NeovimWrite = Text -> Neovim r st ()

consumeLoop :: Server -> NeovimRead -> NeovimWrite -> Neovim r st ()
consumeLoop server read write = do
    status <- liftIO $ takeMVar (status server)
    if status == Running
       then loop
       else liftIO $ putMVar (status server) status
  where loop = do
    action <- liftIO $ readaction server
    case action of
      ReadBuffer -> do
        text <- read
        liftIO $ putMVar (buffer server) text
      WriteBuffer -> do
        text <- liftIO $ takeMVar (buffer server)
        write text
    liftIO $ putMVar (status server) Running
    consumeLoop server read write

Answer 1

loop的主体需要缩进而不是名称。 e.g：

consumeLoop :: Server -> NeovimRead -> NeovimWrite -> Neovim r st ()
consumeLoop server read write = do
    status <- liftIO $ takeMVar (status server)
    if status == Running
       then loop
       else liftIO $ putMVar (status server) status
  where
    loop = do
      action <- liftIO $ readaction server
      ...

Haskell缩进块＆＃34; do-block中的最后一个语句必须是一个表达式＆＃34;

1 个答案: