Replace case of with do blocks for Either

006_hindley_milner.md

@@ -250,9 +250,9 @@ type scheme.
 
 ```haskell
 runInfer :: Infer (Subst, Type) -> Either TypeError Scheme
-runInfer m = case evalState (runExceptT m) initUnique of
-  Left err  -> Left err
-  Right res -> Right $ closeOver res
+runInfer m = do
+  res <- evalState (runExceptT m) initUnique
+  return (closeOver res)
 ```
 
 Substitution

CONTRIBUTORS.md

@@ -15,3 +15,4 @@ Contributors
 * Christian Sievers
 * Franklin Chen
 * Jake Taylor
+* Oskar Wickström

chapter7/poly/Infer.hs

@@ -31,9 +31,9 @@ data TypeError
   | GenericTypeError
 
 runInfer :: Infer (Subst, Type) -> Either TypeError Scheme
-runInfer m = case evalState (runExceptT m) initUnique of
-  Left err  -> Left err
-  Right res -> Right $ closeOver res
+runInfer m = do
+  res <- evalState (runExceptT m) initUnique
+  return (closeOver res)
 
 closeOver :: (Map.Map TVar Type, Type) -> Scheme
 closeOver (sub, ty) = normalize sc
@@ -190,9 +190,9 @@ inferExpr env = runInfer . infer env
 
 inferTop :: TypeEnv -> [(String, Expr)] -> Either TypeError TypeEnv
 inferTop env [] = Right env
-inferTop env ((name, ex):xs) = case (inferExpr env ex) of
-  Left err -> Left err
-  Right ty -> inferTop (extend env (name, ty)) xs
+inferTop env ((name, ex):xs) = do
+  ty <- (inferExpr env ex)
+  inferTop (extend env (name, ty)) xs
 
 normalize :: Scheme -> Scheme
 normalize (Forall ts body) = Forall (fmap snd ord) (normtype body)

chapter7/poly_constraints/Infer.hs

@@ -100,21 +100,18 @@ runInfer env m = runExcept $ evalRWST m env initInfer
 
 -- | Solve for the toplevel type of an expression in a given environment
 inferExpr :: Env -> Expr -> Either TypeError Scheme
-inferExpr env ex = case runInfer env (infer ex) of
-  Left err -> Left err
-  Right (ty, cs) -> case runSolve cs of
-    Left err -> Left err
-    Right subst -> Right $ closeOver $ apply subst ty
+inferExpr env ex = do
+  (ty, cs) <- runInfer env (infer ex)
+  subst <- runSolve cs
+  return (closeOver (apply subst ty))
 
 -- | Return the internal constraints used in solving for the type of an expression
 constraintsExpr :: Env -> Expr -> Either TypeError ([Constraint], Subst, Type, Scheme)
-constraintsExpr env ex = case runInfer env (infer ex) of
-  Left err -> Left err
-  Right (ty, cs) -> case runSolve cs of
-    Left err -> Left err
-    Right subst -> Right $ (cs, subst, ty, sc)
-      where
-        sc = closeOver $ apply subst ty
+constraintsExpr env ex = do
+  (ty, cs) <- runInfer env (infer ex)
+  subst <- runSolve cs
+  let sc = closeOver $ apply subst ty
+  return (cs, subst, ty, sc)
 
 -- | Canonicalize and return the polymorphic toplevel type.
 closeOver :: Type -> Scheme
@@ -217,9 +214,9 @@ infer expr = case expr of
 
 inferTop :: Env -> [(String, Expr)] -> Either TypeError Env
 inferTop env [] = Right env
-inferTop env ((name, ex):xs) = case (inferExpr env ex) of
-  Left err -> Left err
-  Right ty -> inferTop (extend env (name, ty)) xs
+inferTop env ((name, ex):xs) = do
+  ty <- (inferExpr env ex)
+  inferTop (extend env (name, ty)) xs
 
 normalize :: Scheme -> Scheme
 normalize (Forall _ body) = Forall (map snd ord) (normtype body)

chapter7/poly_constraints/poly.cabal

@@ -9,14 +9,14 @@ extra-source-files:  README.md
 cabal-version:       >=1.10
 
 executable poly
-  build-depends:       
-      base          >= 4.6   && <4.7
-    , pretty        >= 1.1   && <1.2
-    , parsec        >= 3.1   && <3.2
-    , text          >= 1.2   && <1.3
-    , containers    >= 0.5   && <0.6
-    , mtl           >= 2.2   && <2.3
-    , transformers  >= 0.4.2 && <0.5
+  build-depends:
+      base          >= 4.6   && <= 4.9
+    , pretty        >= 1.1   &&  < 1.2
+    , parsec        >= 3.1   &&  < 3.2
+    , text          >= 1.2   &&  < 1.3
+    , containers    >= 0.5   &&  < 0.6
+    , mtl           >= 2.2   &&  < 2.3
+    , transformers  >= 0.4.2 &&  < 0.5
     , repline       >= 0.1.2.0
   default-language:    Haskell2010
   main-is:             Main.hs