Add the haskell book

Haskell-book/02/src/Main.purs

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+module Main where
+
+import Prelude
+import Control.Monad.Eff (Eff)
+import Control.Monad.Eff.Console (CONSOLE, log)
+import Math (pi)
+
+--
+-- 2.5 Comprehensive check
+--
+mulSquare :: Number -> Number
+mulSquare x = pi * (x * x)
+
+waxOn :: Int
+waxOn = x * 5
+  where x = y * y
+        y = z + 8
+        z = 7
+
+triple :: Int -> Int
+triple x = x * 3
+
+waxOff :: Int -> Int
+waxOff = triple
+
+main :: forall e. Eff (console :: CONSOLE | e) Unit
+main = do
+  log "Hello sailor!"