Fix Haskell example

http://nixos.org redirects to https://nixos.org and apparently the HTTP library doesn't follow the redirect, so the output is empty.
When defining https in the request it crashes because the library doesn't seem to support https.
So this switches the example to a different http library.

1 files changed, 8 insertions, 7 deletions

diff --git a/doc/manual/src/command-ref/nix-shell.md b/doc/manual/src/command-ref/nix-shell.md
index 88b675e71..938d56e6e 100644
--- a/doc/manual/src/command-ref/nix-shell.md
+++ b/doc/manual/src/command-ref/nix-shell.md
@@ -232,22 +232,23 @@ terraform apply
 > in a nix-shell shebang.
 
 Finally, using the merging of multiple nix-shell shebangs the following
-Haskell script uses a specific branch of Nixpkgs/NixOS (the 18.03 stable
+Haskell script uses a specific branch of Nixpkgs/NixOS (the 20.03 stable
 branch):
 
 ```haskell
 #! /usr/bin/env nix-shell
-#! nix-shell -i runghc -p "haskellPackages.ghcWithPackages (ps: [ps.HTTP ps.tagsoup])"
-#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-18.03.tar.gz
+#! nix-shell -i runghc -p "haskellPackages.ghcWithPackages (ps: [ps.download-curl ps.tagsoup])"
+#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-20.03.tar.gz
 
-import Network.HTTP
+import Network.Curl.Download
 import Text.HTML.TagSoup
+import Data.Either
+import Data.ByteString.Char8 (unpack)
 
 -- Fetch nixos.org and print all hrefs.
 main = do
-  resp <- Network.HTTP.simpleHTTP (getRequest "http://nixos.org/")
-  body <- getResponseBody resp
-  let tags = filter (isTagOpenName "a") $ parseTags body
+  resp <- openURI "https://nixos.org/"
+  let tags = filter (isTagOpenName "a") $ parseTags $ unpack $ fromRight undefined resp
   let tags' = map (fromAttrib "href") tags
   mapM_ putStrLn $ filter (/= "") tags'
 ```