2 files changed, 98 insertions, 0 deletions
diff --git a/users/Profpatsch/reverse-haskell-deps.hs b/users/Profpatsch/reverse-haskell-deps.hs
new file mode 100644
index 000000000000..6b644df9ecc6
--- /dev/null
+++ b/users/Profpatsch/reverse-haskell-deps.hs
@@ -0,0 +1,72 @@
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE MultiWayIf #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+import qualified Text.HTML.TagSoup as Tag
+import qualified Data.Text as Text
+import Data.Text (Text)
+import qualified Data.List as List
+import Data.Maybe
+import Text.Nicify
+import qualified Text.Read as Read
+import Numeric.Natural
+import Data.Either
+import qualified Data.ByteString as ByteString
+import qualified Data.Text.Encoding
+
+parseNat :: Text.Text -> Maybe Natural
+parseNat = Read.readMaybe . Text.unpack
+
+printNice :: Show a => a -> IO ()
+printNice = putStrLn . nicify . show
+
+type Tag = Tag.Tag Text.Text
+
+main = do
+  reverseHtml <- readStdinUtf8
+  printNice $ List.sortOn snd $ packagesAndReverseDeps reverseHtml
+
+  where
+    readStdinUtf8 = Data.Text.Encoding.decodeUtf8 <$> ByteString.getContents
+
+-- | reads the table provided by https://packdeps.haskellers.com/reverse
+-- figuring out all sections (starting with the link to the package name),
+-- then figuring out the name of the package and the first column,
+-- which is the number of reverse dependencies of the package
+packagesAndReverseDeps reverseHtml = do
+  let tags = Tag.parseTags reverseHtml
+  let sections =  Tag.partitions (isJust . reverseLink) tags
+  let sectionNames = map (fromJust . reverseLink . head) sections
+  mapMaybe
+    (\(name :: Text.Text, sect) -> do
+        reverseDeps <- firstNaturalNumber sect
+        pure (sectionPackageName name sect, reverseDeps) :: Maybe (Text.Text, Natural))
+    $ zip sectionNames sections
+
+
+  where
+    reverseLink = \case
+      Tag.TagOpen "a" attrs -> mapFind attrReverseLink attrs
+      _ -> Nothing
+
+    attrReverseLink = \case
+      ("href", lnk) -> if
+          | "packdeps.haskellers.com/reverse/" `Text.isInfixOf` lnk -> Just lnk
+          | otherwise -> Nothing
+      _ -> Nothing
+
+    sectionPackageName :: Text -> [Tag] -> Text
+    sectionPackageName sectionName = \case
+      (_: Tag.TagText name : _) -> name
+      (_: el : _) -> sectionName
+      xs -> sectionName
+
+
+    firstNaturalNumber :: [Tag] -> Maybe Natural
+    firstNaturalNumber =
+      mapFind (\case
+        Tag.TagText t -> parseNat t
+        _ -> Nothing)
+
+    mapFind :: (a -> Maybe b) -> [a] -> Maybe b
+    mapFind f xs = fromJust . f <$> List.find (isJust . f) xs
diff --git a/users/Profpatsch/reverse-haskell-deps.nix b/users/Profpatsch/reverse-haskell-deps.nix
new file mode 100644
index 000000000000..b47347ea9fea
--- /dev/null
+++ b/users/Profpatsch/reverse-haskell-deps.nix
@@ -0,0 +1,26 @@
+{ depot, pkgs, ... }:
+
+# Parses https://packdeps.haskellers.com/reverse
+# and outputs the amount of reverse dependencies of each hackage package.
+
+let
+
+  rev = depot.nix.writeExecline "reverse-haskell-deps" {} [
+    "pipeline" [
+      "${pkgs.curl}/bin/curl" "-L" "https://packdeps.haskellers.com/reverse"
+    ]
+    rev-hs
+
+  ];
+
+  rev-hs = pkgs.writers.writeHaskell "revers-haskell-deps-hs" {
+    libraries =  [
+      pkgs.haskellPackages.nicify-lib
+      pkgs.haskellPackages.tagsoup
+    ];
+
+  }
+    ./reverse-haskell-deps.hs;
+
+
+in rev