Major progress on laws

Calculator.hs

@@ -5,11 +5,17 @@ import Expr
 import Parser
 
 data Law = Law LawName Equation
- deriving Show
 
 type LawName = String
 type Equation = (Expr,Expr)
 
+instance Show Law where
+  showsPrec _ (Law name (e1, e2)) =
+    showString (name ++ ": ")
+      . shows e1
+      . showString " = "
+      . shows e2
+
 law :: Parser Law
 law = do name <- upto ':'
          eqn <- equation
@@ -20,3 +26,21 @@ equation = do lh <- expr
               symbol "="
               rh <- expr
               return (lh, rh)
+
+sortLaws :: [Law] -> [Law]
+sortLaws laws = simple ++ others ++ defn
+  where (simple, nonsimple) = partition isSimple laws
+        (defn, others) = partition isDefn nonsimple
+
+isSimple, isDefn :: Law -> Bool
+
+isSimple (Law _ (Compose a, Compose b))
+  = length a > length b
+
+isDefn d = case d of
+  (Law _ (Compose [Con f es], _)) -> all Calculator.isVar es
+  _ -> False
+
+isVar v = case v of
+          (Compose [Var _]) -> True
+          _ -> False