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我开始学习 Haskell 语言和 Yesod Web 框架。但是，当我尝试对 mkYesod 使用“parseRoutesNoCheck”时，编译器无法匹配 parseRoutesNoCheck 的返回类型（资源）。

$ ghc simple_yesod.hs
[1 of 1] Compiling Main             ( simple_yesod.hs, simple_yesod.o )
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
Loading package bytestring-0.9.1.10 ... linking ... done.
Loading package array-0.3.0.2 ... linking ... done.
Loading package containers-0.4.0.0 ... linking ... done.
Loading package deepseq-1.1.0.2 ... linking ... done.
Loading package text-0.11.0.6 ... linking ... done.
Loading package path-pieces-0.0.0 ... linking ... done.
Loading package pretty-1.0.1.2 ... linking ... done.
Loading package template-haskell ... linking ... done.
Loading package web-routes-quasi-0.7.1 ... linking ... done.

simple_yesod.hs:9:36:
    Couldn't match expected type `yesod-core-0.9.2:Yesod.Internal.RouteParsing.Resource'
                with actual type `Resource'
    In the return type of a call of `Resource'
    In the expression:
      Resource "PageR" [StaticPiece "page", SinglePiece "String"] ["GET"]
    In the second argument of `mkYesod', namely
      `[Resource
          "PageR" [StaticPiece "page", SinglePiece "String"] ["GET"],
        Resource
          "UserR" [StaticPiece "user", SinglePiece "String"] ["GET"]]'

看来我使用了错误的 parseRoutesNoCheck，但正确的模块在哪里？

simple_yesod.hs 如下。

{-# LANGUAGE TypeFamilies, QuasiQuotes, TemplateHaskell, MultiParamTypeClasses, OverloadedStrings #-}
import Yesod
import Web.Routes.Quasi.Parse
import qualified Text.Blaze.Html5 as H

data Test = Test {
  }

mkYesod "Test" [parseRoutesNoCheck|
/page/#String      PageR   GET
/user/#String      UserR   GET
|]

instance Yesod Test where
  approot _ = "" 
  defaultLayout widget = do
                      content <- widgetToPageContent widget
                      hamletToRepHtml [hamlet|
\<!DOCTYPE html>

<html>
  <head>
    <title>#{pageTitle content}
  <body>
    <ul id="navbar">
    <div id="content">
      \^{pageBody content}
|]


getUserR :: String -> Handler RepHtml
getUserR userName = defaultLayout
                    (do
                      setTitle $ H.toHtml $ "Hello " ++ userName
                      addHamlet $ html userName
                    )
    where
      html page = [hamlet|
 <h1>User: #{userName}
 <p>This page is for user: #{userName}
 |]

getPageR :: String -> Handler RepHtml
getPageR pageName = defaultLayout
                    (do
                      setTitle $ H.toHtml $ "Article: " ++ pageName
                      addHamlet $ html pageName
                    )
    where
      html page = [hamlet|
 <h1>Page: #{pageName}
 <p>This page is for page: #{pageName}
 |]

main :: IO ()
main = do
  warpDebug 3000 $ Test

我正在使用 Glasgow Haskell 编译器，版本 7.0.3 和 yesod-core-0.9.2。

4

1 回答 1

2

您应该简单地使用parseRoutes而不是parseRoutesNoCheck. 此外，您可能需要添加module Main where和删除import Web.Routes.Quasi.Parse，因为Yesod模块已经导出parseRoutes。

这是我提到的修改的完整代码。

{-# LANGUAGE TypeFamilies, QuasiQuotes, TemplateHaskell, MultiParamTypeClasses, OverloadedStrings #-}
module Main where
import Yesod
import qualified Text.Blaze.Html5 as H


data Test = Test {
  }

mkYesod "Test" [parseRoutes|
/page/#String      PageR   GET
/user/#String      UserR   GET
|]

instance Yesod Test where
  approot _ = "" 
  defaultLayout widget = do
                      content <- widgetToPageContent widget
                      hamletToRepHtml [hamlet|
\<!DOCTYPE html>

<html>
  <head>
    <title>#{pageTitle content}
  <body>
    <ul id="navbar">
    <div id="content">
      \^{pageBody content}
|]


getUserR :: String -> Handler RepHtml
getUserR userName = defaultLayout
                    (do
                      setTitle $ H.toHtml $ "Hello " ++ userName
                      addHamlet $ html userName
                    )
    where
      html page = [hamlet|
 <h1>User: #{userName}
 <p>This page is for user: #{userName}
 |]

getPageR :: String -> Handler RepHtml
getPageR pageName = defaultLayout
                    (do
                      setTitle $ H.toHtml $ "Article: " ++ pageName
                      addHamlet $ html pageName
                    )
    where
      html page = [hamlet|
 <h1>Page: #{pageName}

一个好主意是当您处于 Yesod 的学习阶段（以及与此相关的所有其他内容）时，尝试复制现有示例。代码片段通常可以在 Yesod 书或 github 存储库中找到，可以从这些资源中学习。

编辑：我缺乏完整的答案。显然现在parseRoutesand 家族位于“Yesod.Dispatch”中，它只是从隐藏模块Yesod.Internal.RouteParsing 重新导出。parseRoutesNoCheck在中定义Yesod.Internal.RouteParsing但从未公开，因为您可能总是希望检查非重叠路由。

我希望这能澄清一点。

于 2011-10-02T08:05:38.770 回答