Rewrite eval for AExpr

4 files changed, 5 insertions, 12 deletions

diff --git a/paper/While/Common.dcl b/paper/While/Common.dcl
index db71353..876ffdd 100644
--- a/paper/While/Common.dcl
+++ b/paper/While/Common.dcl
@@ -32,7 +32,6 @@ instance toString Error
 (<+) infixr 5 :: a b -> String | toString a & toString b
 
 ($) infixr 0 :: (a -> b) a -> b
-(on) infix 0 :: (b -> c) (a a -> b) -> (a a -> c)
 
 (*>) infixl 4 :: (f a) (f b) -> f b | Applicative f
 (<*) infixl 4 :: (f a) (f b) -> f a | Applicative f
diff --git a/paper/While/Common.icl b/paper/While/Common.icl
index 2c28933..4f6e4c4 100644
--- a/paper/While/Common.icl
+++ b/paper/While/Common.icl
@@ -28,9 +28,6 @@ where
 ($) infixr 0 :: (a -> b) a -> b
 ($) f x = f x
 
-(on) infix 0 :: (b -> c) (a a -> b) -> (a a -> c)
-(on) f g = \x y -> f (g x y)
-
 (*>) infixl 4 :: (f a) (f b) -> f b | Applicative f
 (*>) fa fb = const id <$> fa <*> fb
 
diff --git a/paper/While/WhileCommon.icl b/paper/While/WhileCommon.icl
index ce4f8fe..1fbebc3 100644
--- a/paper/While/WhileCommon.icl
+++ b/paper/While/WhileCommon.icl
@@ -46,13 +46,10 @@ where
 		= eval a1 st >>= \r1 ->
 		  eval a2 st >>= app op r1
 	where
-		app :: Operator -> Int Int -> Either Error Int
-		app Add = pure on (+)
-		app Sub = pure on (-)
-		app Mul = pure on (*)
-		app Div = \i j -> if (j == 0)
-			(Left (Runtime "Division by 0"))
-			(pure (i / j))
+		app :: Operator Int Int -> Either Error Int
+		app Div i 0 = Left (Runtime "Division by 0")
+		app op  i j = Right $ (case op of
+			Add = (+); Sub = (-); Mul = (*); Div = (/)) i j
 
 instance eval BExpr Bool
 where
diff --git a/paper/eval.tex b/paper/eval.tex
index 14246f8..969a82d 100644
--- a/paper/eval.tex
+++ b/paper/eval.tex
@@ -11,7 +11,7 @@ occurs in the \CI{State} function, while the latter will occur in the \CI{eval}
 implementation of \CI{AExpr}. Using monads, we can easily pass through errors.
 An example will clarify:
 
-\lstinputlisting[firstline=40,lastline=55]{While/WhileCommon.icl}
+\lstinputlisting[firstline=40,lastline=52]{While/WhileCommon.icl}
 
 Recall that the second argument to \CI{eval}, here \CI{st}, is of type
 \CI{State}. That is, it is a function that yields an \CI{Either Error Int}. In