praxis

commit 2e321fc7c01f52f4325bf7bffd450cf0c07f0621
parent 949a0ad5e1180ce8a9f8afbbb230a55099df6dae
Author: Jared Tobin <jared@jtobin.ca>
Date:   Sat,  7 Jul 2018 13:12:18 +1200

Add pi estimating exercise.

Diffstat:
A
20180705_estimate_pi/Pi.hs
 | 
37
+++++++++++++++++++++++++++++++++++++
M
20180706_scores/Scores.hs
 | 
6
++++++

2 files changed, 43 insertions(+), 0 deletions(-)
diff --git a/20180705_estimate_pi/Pi.hs b/20180705_estimate_pi/Pi.hs
@@ -0,0 +1,37 @@
+{-# OPTIONS_GHC -Wall -fno-warn-type-defaults #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+import Control.Monad.Primitive (PrimMonad, PrimState)
+import System.Random.MWC as MWC
+import qualified Control.Foldl as L
+import Pipes ((>->))
+import qualified Pipes as P
+import qualified Pipes.Prelude as P
+
+sample :: forall m. PrimMonad m => Gen (PrimState m) -> P.Producer Bool m ()
+sample prng = do
+    val <- P.lift (relPrime prng)
+    P.yield val
+    sample prng
+  where
+    relPrime rng =
+      rprime <$> (uniform rng :: m Word) <*> (uniform rng :: m Word)
+
+    rprime a b = gcd a b == 1
+
+count :: Num a => L.Fold Bool a
+count = L.Fold alg 0 id where
+  alg acc tru
+    | tru       = acc + 1
+    | otherwise = acc
+
+avg :: Fractional a => L.Fold Bool a
+avg = (/) <$> count <*> L.genericLength
+
+main :: IO ()
+main = do
+  prng <- createSystemRandom
+  freq <- L.purely P.fold avg (sample prng >-> P.take 1000000)
+
+  print (sqrt (6 / freq))
+
diff --git a/20180706_scores/Scores.hs b/20180706_scores/Scores.hs
@@ -51,6 +51,12 @@ test = [
   , ("Rachel", 99)
   , ("Rachel", 100)
   , ("Rachel", 81)
+  , ("Deanie", 99)
+  , ("Deanie", 75)
+  , ("Deanie", 76)
+  , ("Deanie", 74)
+  , ("Deanie", 43)
+  , ("Deanie", 69)
   ]
 
 main :: IO ()