无法解析模块:意外=在第1列或输入结尾处期望凹痕

Question

编写此代码

module Main where
import Prelude
import Data.List (List)
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Console (CONSOLE, log)
type Entry = {
  firstName :: String,
  lastName :: String,
  address :: Address
}
type Address = {
  street :: String,
  city :: String,
  state :: String
}
type AddressBook = List Entry
showEntry :: Entry -> String
showEntry entry = entry.lastName <> ", " <>
                  entry.firstName <> ", " <>
                  showAddress entry.address
showAddress :: Address -> String                  
showAddress address = address.street <> ", " <>
                      address.city <> ", " <> 
                      address.state
main :: forall e. Eff (console :: CONSOLE | e) Unit
main = do
  log "Hello Sailor!"
  address = {street: "123 Fake St.", city: "Faketown", state: "CA"}
  showAddress address

一切都缩进了两个空间

我有错误

Error found:
at src/Main.purs line 34, column 11 - line 34, column 11
  Unable to parse module:
  unexpected =
  expecting indentation at column 1 or end of input

See https://github.com/purescript/documentation/blob/master/errors/ErrorParsingModule.md for more information,
or to contribute content related to this error.

我也尝试了

main = do
  log "Hello Sailor!"
  address :: Address 
  address = {street: "123 Fake St.", city: "Faketown", state: "CA"}
  showAddress address

，但仍然会遇到相同的错误。

Answer 1

您不能在do符号内具有蓝色的绑定，或者实际上除了顶级外，其他任何地方。

如果要命名一个中间值，则必须使用let：

main = do
  log "Hello Sailor!"
  let address = {street: "123 Fake St.", city: "Faketown", state: "CA"}
  showAddress address

在您的情况下，由于address不取决于上一个代码，因此您也可以使用where绑定：

main = do
  log "Hello Sailor!"
  showAddress address
  where
      address = {street: "123 Fake St.", city: "Faketown", state: "CA"}

，即使在最高级别，您也无法拥有自己的绑定。看到module Main之后的where？这意味着该模块内的所有内容都是where -Bound。

因此，正确的说明就是这样：绑定永远无法独自站立，它们始终必须是 let - 或 where -bound。

还注意：您可以在单个let或单个where中具有多个绑定：

f x = do
    let y = a + 42
        z = y * b
    pure $ z - 3
    where
         a = x + 1
         b = a * 2