Fleshed out the tests and infrastructure

main/Main.hs

@@ -3,8 +3,11 @@ module Main where
 import Interpreter ( eval )
 import Parser ( parseExpr )
 
+fromEither :: (e -> a) -> Either e a -> a
+fromEither err = either err id
+
 calc :: String -> (String -> Int) -> Int
-calc e = eval (parseExpr e)
+calc e = eval (fromEither error (parseExpr e))
 
 main :: IO ()
 main = do

src/Parser.hs

@@ -1,5 +1,7 @@
 module Parser where
 
+import Prelude hiding (negate)
+
 import WeakAST
 import Miniparsec
 
@@ -7,5 +9,5 @@ import Miniparsec
 This function should turn a string into an expression.
 -}
 -- Should be a good issue for a newcomer?
-parseExpr :: String -> Expr
-parseExpr = error "Not implemented yet :("
+parseExpr :: String -> Either String Expr
+parseExpr = undefined

test/common/Arbitrary.hs

@@ -1,9 +1,11 @@
-{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeApplications, StandaloneDeriving, DeriveGeneric #-}
 module Arbitrary where
 
 import qualified WeakAST as Weak
 import qualified StrongAST as Strong
 
+import GHC.Generics
+
 import Convert (strengthen)
 
 import Test.Tasty.QuickCheck
@@ -33,8 +35,25 @@ instance Arbitrary Weak.Expr where
                      ]
         where
           subexpr = expr (n `div` 2)
+  shrink (Weak.Var v) = []
+  shrink e            = genericShrink e
 
-instance Arbitrary Strong.Expr where arbitrary = fmap strengthen arbitrary
-instance Arbitrary Strong.Term where arbitrary = fmap strengthen arbitrary
-instance Arbitrary Strong.Negate where arbitrary = fmap strengthen arbitrary
-instance Arbitrary Strong.Atom where arbitrary = fmap strengthen arbitrary
+instance Arbitrary Strong.Expr where
+  arbitrary = fmap strengthen arbitrary
+  shrink = genericShrink
+instance Arbitrary Strong.Term where
+  arbitrary = fmap strengthen arbitrary
+  shrink = genericShrink
+instance Arbitrary Strong.Negate where
+  arbitrary = fmap strengthen arbitrary
+  shrink = genericShrink
+instance Arbitrary Strong.Atom where
+  arbitrary = fmap strengthen arbitrary
+  shrink (Strong.Num n) = map Strong.Num (shrink n)
+  shrink (Strong.Var v) = []
+  shrink (Strong.Parens x) = map Strong.Parens (shrink x)
+
+deriving instance Generic Weak.Expr
+deriving instance Generic Strong.Expr
+deriving instance Generic Strong.Term
+deriving instance Generic Strong.Negate

test/parser/Main.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE FlexibleInstances #-}
 module Main where
 
 import Arbitrary
@@ -14,4 +15,10 @@ main = defaultMain $ testGroup "Conversions" [
     --testProperty "parse . pretty = id" roundtrip
   ]
 
-roundtrip e = parseExpr (pretty e) === e
+newtype MakeNice a = MakeNice a deriving Eq
+
+instance Pretty e => Show (MakeNice (Either String e)) where
+  show (MakeNice (Right e)) = pretty e
+  show (MakeNice (Left err)) = err
+
+roundtrip e = MakeNice (parseExpr (pretty e)) === MakeNice (Right e)