Add Koan about Stdin clock

koans/basic/9-input/Koan.hs

@@ -0,0 +1,46 @@
+{- | Input!
+
+We want to react to user input. For this track, let's allow the program to interact on the console.
+To do this, meditate about the follow sentence:
+
+Events in Rhine come from event clocks.
+
+An event happens when an event clock ticks.
+For example, to react every time when a line is entered on the standard input,
+you have to add the 'Stdin' event clock to your main Rhine.
+
+Events are handled just like any other kind of data.
+The difference between event clocks and clocks like 'Millisecond n' is only conceptual:
+A fixed rate clock ticks at predictable intervals,
+whereas it depends on the user or another external influence when an event clock ticks.
+The frameworks handles them in the same way.
+
+The next Koans are about the event that is triggered when a line of text is entered on the standard input.
+-}
+module Koan where
+
+-- text
+import Data.Text.IO as Text (putStrLn)
+
+-- rhine
+import FRP.Rhine
+
+{- | A line of user input.
+
+The 'Stdin' clock ticks every time a line is entered on stdin.
+
+The information _what_ was typed can be retrieved with a special signal function: 'tagS'.
+This signal function is a "sensor" (it has no input, only output),
+and it produces different data depending on the clock.
+For 'Stdin', it is one line of standard input.
+-}
+userInput :: ClSF IO Stdin () Text
+userInput = tagS
+
+-- | Output the same line that was just entered.
+parrot :: ClSF IO Stdin () ()
+-- Do you remember how to convert an effectful function into a ClSF?
+parrot = userInput >-> _ Text.putStrLn
+
+main :: IO ()
+main = flow mainRhine

koans/basic/9-input/Test.hs

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+module Main where
+
+-- rhine-koan
+import Koan qualified (main)
+
+-- test-io
+import TestIO
+
+main :: IO ()
+main = testForSeconds 2 Nothing Koan.main $ \output ->
+  case length (filter (== "Hello Rhine!") output) of
+    10 -> []
+    0 -> ["Your program didn't produce the line \"Hello Rhine!\" in time. Maybe a typo?"]
+    n
+      | n < 10 ->
+          [ "Your program seems to be running a bit slow."
+          , "Only " ++ show n ++ " messages arrived."
+          ]
+    _ -> ["It seems the clock is ticking too fast."]