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Fix Haskell example

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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.
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Mauricio Scheffer 2021-02-16 23:19:42 +00:00 committed by GitHub
parent 4e98f0345c
commit 35129884f9
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15
doc/manual/src/command-ref/nix-shell.md
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@ -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'
```