我怎样才能 print/encode 一个值到 Dhall？

Question

{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE OverloadedStrings #-}

import Dhall

data Example = Example { foo :: Natural, bar :: Vector Double }
    deriving (Generic, Show)

instance Interpret Example

main :: IO ()
main = do
  putStrLn "Hello, Haskell!"
  x <- input auto "./example.dhall"
  print (x :: Example)

在上面的示例中，我如何才能将 Example 编码为 dhall 值，因此本质上是 Example -> String 类型的函数？似乎无法在黑线鳕中找到任何关于打印/编码的参考。

Answer 1

这就是您如何 pretty-print 一个 Haskell 值作为等效的 Dhall 表达式：

{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE DeriveAnyClass    #-}
{-# LANGUAGE OverloadedStrings #-}

import Dhall (FromDhall, Natural, ToDhall, Vector)
import Dhall.Pretty (CharacterSet(..))
import GHC.Generics (Generic)

import qualified Data.Text.Prettyprint.Doc.Render.Text as Prettyprint.Text
import qualified Dhall
import qualified Dhall.Pretty
import qualified Dhall.Core

data Example = Example { foo :: Natural, bar :: Vector Double }
    deriving (FromDhall, Generic, Show, ToDhall)

main :: IO ()
main = do
  x <- Dhall.input Dhall.auto "./example.dhall"

  let expression = Dhall.embed Dhall.inject (x :: Example)

  let doc = Dhall.Pretty.prettyCharacterSet Unicode expression

  Prettyprint.Text.putDoc doc

我怎样才能 print/encode 一个值到 Dhall？

How can I print/encode a value into Dhall?

haskell

dhall