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Writing haskell scripts with a nix-shell shebang line
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:set -fwarn-unused-binds -fwarn-unused-imports | |
:set -i. | |
:load Request |
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#! /usr/bin/env nix-shell | |
#! nix-shell -p "haskell.packages.ghc802.ghcWithPackages (pkgs: with pkgs; [ aeson HTTP ])" | |
#! nix-shell --pure | |
#! nix-shell -i runghc | |
{-# LANGUAGE LambdaCase #-} | |
{-# LANGUAGE OverloadedStrings #-} | |
module Main where | |
{-| Easy, clean Haskell scripting. Courtesy of Nix. | |
Need some help from ghcid? Fire up your editor from... | |
$ nix-shell -p "haskell.packages.ghc802.ghcWithPackages (pkgs: with pkgs; [ ghcid aeson HTTP ])" | |
Okay cool, but wtf version of these packages am I using? | |
$ ghc-pkg list | |
-} | |
import Data.Aeson ((.:)) | |
import qualified Data.Aeson as Aeson | |
import qualified Data.ByteString.Lazy.Char8 as ByteString | |
import qualified Network.HTTP as HTTP | |
import qualified System.IO as IO | |
main :: IO.IO () | |
main = (decodePosts <$> fetchPosts) >>= \case | |
Left err -> IO.hPutStrLn IO.stderr err | |
Right posts -> IO.print (length posts) | |
fetchPosts :: IO ByteString.ByteString | |
fetchPosts = | |
do response <- HTTP.simpleHTTP (HTTP.getRequest url) | |
HTTP.getResponseBody response <#> ByteString.pack | |
where | |
url = "http://jsonplaceholder.typicode.com/posts" | |
decodePosts :: ByteString.ByteString -> Either String [Post] | |
decodePosts = Aeson.eitherDecode' | |
data Post = Post | |
{ userID :: Int | |
, postID :: Int | |
, title :: String | |
, body :: String | |
} deriving (Show) | |
instance Aeson.FromJSON Post where | |
parseJSON = Aeson.withObject "Post" $ \v -> Post | |
<$> v .: "userId" | |
<*> v .: "id" | |
<*> v .: "title" | |
<*> v .: "body" | |
(<#>) = flip fmap |
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