Split code into modules

Also did some work on laws

Expr.hs

@@ -0,0 +1,47 @@
+{-# LANGUAGE LambdaCase #-}
+
+module Expr where
+
+import Data.Char
+import Utils
+
+newtype Expr = Compose [Atom]
+  deriving Eq
+data Atom = Var VarName | Con ConName [Expr]
+  deriving Eq
+
+type VarName = String
+type ConName = String
+
+
+
+instance Show Expr where
+  showsPrec p (Compose []) = showString "id"
+  showsPrec p (Compose [a]) = showsPrec p a
+  showsPrec p (Compose as)
+    = showParen (p>0) (showSep " . " (showsPrec 1) as)
+
+compose :: [ShowS] -> ShowS
+compose = foldr (.) id
+
+showSep :: String -> (a -> ShowS) -> [a] -> ShowS
+showSep sep f
+  = compose . intersperse (showString sep) . map f
+
+instance Show Atom where
+  showsPrec p (Var v) = showString v
+  showsPrec p (Con f []) = showString f
+  showsPrec p (Con f [l,r])
+    | isOp f = showParen (p>0) (showsPrec 1 l . showSpace
+                                . showString f . showSpace . showsPrec 1 r)
+  showsPrec p (Con f es)
+   = showParen (p>1) (showString f . showSpace . showSep " " (showsPrec 2) es)
+
+showSpace = showChar ' '
+
+isOp f = all symbolic f
+
+intersperse :: a -> [a] -> [a]
+intersperse _ [x] = [x]
+intersperse s (x : xs)
+  = x : s : intersperse s xs