add evaluation tests

haskell-experiments/src/SimpleParser.hs

@@ -55,15 +55,15 @@ eval (UnaryExpr unaryOp a) = lookUpUnaryOp unaryOp (eval a)
 parseExpr :: Parser Expr
 parseExpr =
     makeExprParser
-        parseLiteral
+        parseTerm
         [ [InfixL (char '/' $> BinaryExpr Divide)]
         , [InfixL (char '*' $> BinaryExpr Multiply)]
         , [InfixL (char '+' $> BinaryExpr Add)]
         , [InfixL (char '-' $> BinaryExpr Subtract)]
         ]
 
-parseLiteral :: Parser Expr
-parseLiteral =
+parseTerm :: Parser Expr
+parseTerm =
     choice
         [ Literal <$> decimal
         , between (char '(') (char ')') parseExpr

haskell-experiments/test/Test/SimpleParserSpec.hs

@@ -18,6 +18,11 @@ checkParse :: String -> Expr -> Expectation
 checkParse text expectedExpr = 
   parse parseExpr "" text `shouldBe` Right expectedExpr
 
+checkEval :: String -> Int -> Expectation
+checkEval text expectedVal = 
+  fmap eval (parse parseExpr "" text) `shouldBe` Right expectedVal
+
+
 spec :: Spec
 spec = do
   describe "evaluate expressions" $ do
@@ -39,5 +44,11 @@ spec = do
       checkParse "2+3*5" (BinaryExpr Add (Literal 2) (BinaryExpr Multiply (Literal 3) (Literal 5)))
       checkParse "(2+3)*5" (BinaryExpr Multiply (BinaryExpr Add (Literal 2) (Literal 3)) (Literal 5) )
       checkParse "((2+3))*5" (BinaryExpr Multiply (BinaryExpr Add (Literal 2) (Literal 3)) (Literal 5) )
+    it "can evaluate expressions correctly" $ do
+      checkEval "2" 2
+      checkEval "3*4/2" 6
+      checkEval "2+3*6" 20
+      checkEval "1-2+3" (-4)
+