praxis

commit 690d99a94ea8d9c3fafe97a21fbe5a822e02a26a
parent 9cdb52e7c7113925b6f6b96ae95afb18ad80f4ea
Author: Jared Tobin <jared@jtobin.ca>
Date:   Sun,  8 Jul 2018 17:04:21 +1200

Overengineered exercise thingy.

Diffstat:
A
20180601_exercise/Exercise.hs
 | 
67
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
A
20180601_exercise/grades.dat
 | 
9
+++++++++

2 files changed, 76 insertions(+), 0 deletions(-)
diff --git a/20180601_exercise/Exercise.hs b/20180601_exercise/Exercise.hs
@@ -0,0 +1,67 @@
+{-# OPTIONS_GHC -Wall -fno-warn-type-defaults #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ViewPatterns #-}
+
+import qualified Control.Foldl as L
+import Data.Char as C
+import qualified Data.Foldable as FO
+import qualified Data.Map.Strict as MS
+import Data.Monoid
+import qualified Data.Text as T
+import qualified Data.Text.IO as T
+import qualified Pipes as P
+import qualified Pipes.Prelude as P
+import qualified Pipes.Prelude.Text as PT
+import System.IO
+
+data Record = Record {
+    rnum :: !Int
+  , rcrs :: !T.Text
+  , rgra :: !Int
+  } deriving (Eq, Show)
+
+parse :: T.Text -> Record
+parse (T.strip -> line) =
+  case T.splitOn "|" line of
+    [tnum, rcrs, tgra] ->
+      let rnum = parseNum tnum
+          rgra = parseNum tgra
+
+      in  Record {..}
+
+    _ -> error "parse: bad input"
+
+parseNum :: T.Text -> Int
+parseNum =
+    snd . T.foldr alg (1, 0)
+  where
+    alg char (base, acc) =
+      let nbase = base * 10
+          nacc  = acc + C.digitToInt char * base
+      in  (nbase, nacc)
+
+collect :: L.Fold Record (MS.Map T.Text Record)
+collect = L.Fold alg mempty id where
+  alg acc rnew@(Record nnew cnew _) =
+    case MS.lookup cnew acc of
+      Nothing          -> MS.insert cnew rnew acc
+      Just Record {..} ->
+        if   nnew < rnum
+        then MS.insert rcrs rnew acc
+        else acc
+
+render :: Record -> T.Text
+render Record {..} = rcrs <> ": " <> (T.pack . show) rgra
+
+main :: IO ()
+main = do
+  file <- openFile "grades.dat" ReadMode
+
+  let handle = PT.fromHandleLn file
+      pipe   = P.for handle (P.yield . parse)
+
+  result <- L.purely P.fold collect pipe
+
+  mapM_ (T.putStrLn . render) (FO.toList result)
+
diff --git a/20180601_exercise/grades.dat b/20180601_exercise/grades.dat
@@ -0,0 +1,9 @@
+22|Data Structures|45
+23|English|52
+22|English|51
+26|Data Structures|72
+23|Data Structures|61
+21|English|81
+19|Biology|83
+31|Biology|95
+8|English|66