diff --git a/src/Plume/Syntax/Blocks.hs b/src/Plume/Syntax/Blocks.hs
index 4cdd24f..d02fc49 100644
--- a/src/Plume/Syntax/Blocks.hs
+++ b/src/Plume/Syntax/Blocks.hs
@@ -75,9 +75,9 @@ removeUselessBlocks isInner (AST.ELocated e p) = do
   e' <- removeUselessBlocks isInner e
   [AST.ELocated e' p]
 removeUselessBlocks _ (AST.EType ann ts) = [AST.EType ann ts]
-removeUselessBlocks isInner (AST.ETypeExtension gens ann var mems p) = do
+removeUselessBlocks isInner (AST.ETypeExtension gens ann var mems) = do
   let mems' = map (removeUselessBlocksExt isInner) mems
-  [AST.ETypeExtension gens ann var mems' p]
+  [AST.ETypeExtension gens ann var mems']
 removeUselessBlocks _ e = [e]
 
 removeUselessBlocksExt :: (Bool, Bool) -> AST.ExtensionMember -> AST.ExtensionMember
diff --git a/src/Plume/Syntax/Common/Type.hs b/src/Plume/Syntax/Common/Type.hs
index 5a7657e..8028e40 100644
--- a/src/Plume/Syntax/Common/Type.hs
+++ b/src/Plume/Syntax/Common/Type.hs
@@ -79,7 +79,7 @@ pattern TCon s ts = TApp (TId s) ts
 pattern TInt, TBool, TString, TChar, TFloat, TUnit :: PlumeType
 pattern TInt = TId "int"
 pattern TBool = TId "bool"
-pattern TString = TCon "list" [TChar]
+pattern TString = TId "str"
 pattern TChar = TId "char"
 pattern TFloat = TId "float"
 pattern TUnit = TId "unit"
diff --git a/src/Plume/Syntax/Concrete/Expression.hs b/src/Plume/Syntax/Concrete/Expression.hs
index ad3f51e..b5e6051 100644
--- a/src/Plume/Syntax/Concrete/Expression.hs
+++ b/src/Plume/Syntax/Concrete/Expression.hs
@@ -70,8 +70,6 @@ data PostfixOperator
   = PostfixSlice
   deriving (Show, Eq)
 
-type Priority = Integer
-
 -- | A concrete expression is an expression that is used to represent
 -- | a program. It is a more concrete representation of a program than
 -- | an abstract syntax tree. It is used to represent the program in a
@@ -98,7 +96,7 @@ data Expression t f
       interfaceDeduction :: Maybe (Text, Text)
     }
   | EReturn (Expression t f)
-  | ETypeExtension [PlumeGeneric] (Annotation [t]) (Maybe Text) [ExtensionMember t f] Priority
+  | ETypeExtension [PlumeGeneric] (Annotation [t]) (Maybe Text) [ExtensionMember t f]
   | ENativeFunction Text Text [Text] t LibraryType IsStandard
   | ETypeAlias (Annotation [Text]) t
   | EVariableDeclare [PlumeGeneric] Text (f t)
@@ -147,7 +145,7 @@ instance (Eq t, Eq (f t)) => Eq (Expression t f) where
   ESwitch x xs == ESwitch x' xs' = x == x' && xs == xs'
   EReturn x == EReturn y = x == y
   EInterface x xs ys d == EInterface x' xs' ys' d' = x == x' && xs == xs' && ys == ys' && d == d'
-  ETypeExtension xs x t ys p == ETypeExtension xs' x' t' ys' p' = xs == xs' && x == x' && ys == ys' && t == t' && p == p'
+  ETypeExtension xs x t ys == ETypeExtension xs' x' t' ys' = xs == xs' && x == x' && ys == ys' && t == t'
   ENativeFunction x y xs z t isStd == ENativeFunction x' y' xs' z' t' isStd' = x == x' && y == y' && xs == xs' && z == z' && t == t' && isStd == isStd'
   EVariableDeclare xs x t == EVariableDeclare xs' x' t' = xs == xs' && x == x' && t == t'
   ELocated x _ == ELocated y _ = x == y
@@ -182,7 +180,7 @@ instance (Show t, Show (f t)) => Show (Expression t f) where
   show (ESwitch x xs) = "switch " <> show x <> " { " <> S.intercalate "; " (map (\(p, e) -> show p <> " -> " <> show e) xs) <> " }"
   show (EInterface x xs ys d) = "interface " <> show x <> " " <> show xs <> " " <> show ys <> " " <> maybe "" (\(x', y) -> "deduct " <> toString x' <> " " <> toString y) d
   show (EReturn x) = "return " <> show x
-  show (ETypeExtension xs x t ys _) = "extend " <> show xs <> " " <> show x <> " " <> maybe "" ((" as " <>) . toString) t <> " " <> show ys
+  show (ETypeExtension xs x t ys) = "extend " <> show xs <> " " <> show x <> " " <> maybe "" ((" as " <>) . toString) t <> " " <> show ys
   show (ENativeFunction x y xs _ _ _) = "native " <> toString x <> " " <> toString y <> " " <> show xs
   show (ETypeAlias x t) = "type " <> show x <> " = " <> show t
   show (EVariableDeclare xs x t) = "declare " <> show xs <> " " <> toString x <> " " <> show t
diff --git a/src/Plume/Syntax/Concrete/Internal/Pretty.hs b/src/Plume/Syntax/Concrete/Internal/Pretty.hs
index 7a36404..465de4e 100644
--- a/src/Plume/Syntax/Concrete/Internal/Pretty.hs
+++ b/src/Plume/Syntax/Concrete/Internal/Pretty.hs
@@ -98,7 +98,7 @@ prettyExpr _ (ESwitch e ps) =
  where
   prettyCase (p, e') = anCol Blue "case" <+> prettyPat p <+> "=>" <+> prettyExpr 0 e'
 prettyExpr _ (EReturn e) = anCol Blue "return" <+> prettyExpr 0 e
-prettyExpr _ (ETypeExtension gens a var es _) =
+prettyExpr _ (ETypeExtension gens a var es) =
   anCol Blue "extends"
     <> angles (hsep . punctuate comma $ map ansiPretty gens)
       <+> pretty a.annotationName <> angles (hsep . punctuate comma $ map ansiPretty a.annotationValue)
diff --git a/src/Plume/Syntax/Parser/Modules/Literal.hs b/src/Plume/Syntax/Parser/Modules/Literal.hs
index f97093f..707b0e3 100644
--- a/src/Plume/Syntax/Parser/Modules/Literal.hs
+++ b/src/Plume/Syntax/Parser/Modules/Literal.hs
@@ -59,14 +59,10 @@ parseStringWithInterpolation = lexeme $ do
       let y' = combineCharsIntoString y
 
       case (x', y') of
-        (ELiteral (LString a), ELiteral (LString b)) -> stringToList (a <> b)
+        (ELiteral (LString a), ELiteral (LString b)) -> ELiteral (LString (a <> b))
         _ -> EBinary "+" x' y'
-    combineCharsIntoString (ELiteral (LString s)) = stringToList s
     combineCharsIntoString x = x
 
-stringToList :: Text -> Expression
-stringToList xs = EList (map (ELiteral . LChar) (T.unpack xs))
-
 -- | Parse a character literal
 -- | A character literal is a single character enclosed in single quotes
 -- | Example: 'a'
diff --git a/src/Plume/Syntax/Parser/Parser.hs b/src/Plume/Syntax/Parser/Parser.hs
index 6a6bdcb..31ad69d 100644
--- a/src/Plume/Syntax/Parser/Parser.hs
+++ b/src/Plume/Syntax/Parser/Parser.hs
@@ -783,10 +783,8 @@ tExtension = do
 
   tc <- Cmm.Annotation . Cmm.fromText <$> L.identifier <*> L.angles (Typ.tType `P.sepBy1` L.comma) <*> pure False
 
-  Cmm.LInt priority <- P.option (Cmm.LInt 0) $ L.parens (L.reserved "priority" *> Lit.parseInteger)
-
   members <- L.braces (P.many eExtensionMember)
-  return [CST.ETypeExtension gens tc Nothing members priority]
+  return [CST.ETypeExtension gens tc Nothing members]
 
 -- | Parses a type declaration
 -- | A type declaration is a statement that is used to declare a new
diff --git a/src/Plume/Syntax/Require/Resolution.hs b/src/Plume/Syntax/Require/Resolution.hs
index 8b35c19..54bb3a5 100644
--- a/src/Plume/Syntax/Require/Resolution.hs
+++ b/src/Plume/Syntax/Require/Resolution.hs
@@ -257,7 +257,7 @@ checkForUndefined m (HLIR.EMutUpdate n e1 e2) = do
       maybe (pure m') (checkForUndefined m') e2
     else throwError ("Variable " <> toString n' <> " is not defined", pos)
 checkForUndefined m (HLIR.ERequire _) = pure m
-checkForUndefined m (HLIR.ETypeExtension _ ann _ exts _) = do
+checkForUndefined m (HLIR.ETypeExtension _ ann _ exts) = do
   let (var, _) = interpretAnnot ann
 
   unless (isClassDefined 0 var m) $ do
diff --git a/src/Plume/Syntax/Translation/ConcreteToAbstract.hs b/src/Plume/Syntax/Translation/ConcreteToAbstract.hs
index 28adfe7..0c381c8 100644
--- a/src/Plume/Syntax/Translation/ConcreteToAbstract.hs
+++ b/src/Plume/Syntax/Translation/ConcreteToAbstract.hs
@@ -141,11 +141,11 @@ concreteToAbstract (CST.EReturn e) = do
   -- them into a block.
   e' <- fmap interpretSpreadable <$> concreteToAbstract e
   transRet $ AST.EReturn <$> e'
-concreteToAbstract (CST.ETypeExtension g ann var ems p) = do
+concreteToAbstract (CST.ETypeExtension g ann var ems) = do
   ann' <- mapM (mapM transformType) ann
   ems' <-
     fmap flat . sequence <$> mapM concreteToAbstractExtensionMember ems
-  transRet $ AST.ETypeExtension g ann' var <$> ems' <*> pure p
+  transRet $ AST.ETypeExtension g ann' var <$> ems'
 concreteToAbstract (CST.ENativeFunction fp n gens t libTy _) = do
   sc <- readIORef mode
 
diff --git a/src/Plume/Syntax/Translation/Substitution.hs b/src/Plume/Syntax/Translation/Substitution.hs
index 18d7d9c..ca928e5 100644
--- a/src/Plume/Syntax/Translation/Substitution.hs
+++ b/src/Plume/Syntax/Translation/Substitution.hs
@@ -70,12 +70,12 @@ substitute (name, expr) (AST.ESwitch e ps) =
     | name `S.notMember` ftv p = (p, substitute (name, expr) e')
     | otherwise = (p, e')
 substitute (name, expr) (AST.EReturn e) = AST.EReturn (substitute (name, expr) e)
-substitute (name, expr) (AST.ETypeExtension g ann (Just var) ems p)
+substitute (name, expr) (AST.ETypeExtension g ann (Just var) ems)
   | name /= var =
-      AST.ETypeExtension g ann (Just var) (map (substituteExt (name, expr)) ems) p
-  | otherwise = AST.ETypeExtension g ann (Just var) ems p
-substitute (name, expr) (AST.ETypeExtension g ann Nothing ems p) =
-  AST.ETypeExtension g ann Nothing (map (substituteExt (name, expr)) ems) p
+      AST.ETypeExtension g ann (Just var) (map (substituteExt (name, expr)) ems)
+  | otherwise = AST.ETypeExtension g ann (Just var) ems
+substitute (name, expr) (AST.ETypeExtension g ann Nothing ems) =
+  AST.ETypeExtension g ann Nothing (map (substituteExt (name, expr)) ems)
 substitute _ (AST.ENativeFunction fp n gens t st isStd) =
   AST.ENativeFunction fp n gens t st isStd
 substitute _ (AST.EInterface ann gs ms d) = AST.EInterface ann gs ms d
diff --git a/src/Plume/TypeChecker/Checker/Extension.hs b/src/Plume/TypeChecker/Checker/Extension.hs
index a8b8b65..8975aea 100644
--- a/src/Plume/TypeChecker/Checker/Extension.hs
+++ b/src/Plume/TypeChecker/Checker/Extension.hs
@@ -87,7 +87,7 @@ getMapNames ((IsIn _ _, Post.EVariable n _) : xs) = n.identifier : getMapNames x
 getMapNames (_ : xs) = getMapNames xs
 getMapNames [] = []
 
-isInstanceAlreadyDefined :: MonadChecker m => PlumeQualifier -> m (Maybe ([PlumeType], Integer))
+isInstanceAlreadyDefined :: MonadChecker m => PlumeQualifier -> m (Maybe [PlumeType])
 isInstanceAlreadyDefined p = do
   p' <- liftIO $ compressQual p
   MkExtendEnv instances <- gets (extendEnv . environment)
@@ -98,13 +98,13 @@ isInstanceAlreadyDefined p = do
       doesMatchQual p''' p'
 
   case found of
-    Just (IsIn ty _, MkInstance _ _ _ _ priority) -> return (Just (ty, priority))
+    Just (IsIn ty _, _) -> return (Just ty)
     _ -> return Nothing
 
 synthExt :: Infer -> Infer
 synthExt
   infer
-  (Pre.ETypeExtension generics (Annotation tcName tcTy _) _ methods priority) = do
+  (Pre.ETypeExtension generics (Annotation tcName tcTy _) _ methods) = do
     -- Dealing with pre-types and building the qualified qualifiers
     -- for the typeclass instance (used to indicate the instance form and its
     -- superclasses)
@@ -120,8 +120,8 @@ synthExt
     -- Checking if the instance is already defined
     possibleInst <- isInstanceAlreadyDefined instH
     when (isJust possibleInst) $ case possibleInst of
-      Just (ty', p) | p == priority -> throw $ AlreadyDefinedInstance tcName.identifier ty'
-      _ -> pure ()
+      Just ty' -> throw $ AlreadyDefinedInstance tcName.identifier ty'
+      _ -> throw $ CompilerError "Instance already defined"
 
     -- Pre-generating an instance dictionary only based on types
     cls@(MkClass _ _ meths ded) <- findClass tcName.identifier
@@ -138,7 +138,7 @@ synthExt
 
         let quals' = case quals of xs :=>: t -> (xs <> gens) :=>: t
 
-        let preInst = MkInstance qvars quals' mempty finalMethods priority
+        let preInst = MkInstance qvars quals' mempty finalMethods
 
         let qs'' = TypeQuantified <$> qs'
         sub <- liftIO . composeSubs =<< zipWithM unifyAndGetSub qs'' ty
@@ -293,7 +293,7 @@ synthExt
       throw $ UnknownExtensionMethods tcName.identifier unknown
 
     -- Creating the new instance to insert it in the extend environment
-    let inst = MkInstance qvars pred' dict dictFunTys priority
+    let inst = MkInstance qvars pred' dict dictFunTys
     let cls'' = (instH, void inst)
     addClassInstance cls''
 
diff --git a/src/Plume/TypeChecker/Constraints/Typeclass.hs b/src/Plume/TypeChecker/Constraints/Typeclass.hs
index 052853c..36c6116 100644
--- a/src/Plume/TypeChecker/Constraints/Typeclass.hs
+++ b/src/Plume/TypeChecker/Constraints/Typeclass.hs
@@ -41,15 +41,12 @@ discharge cenv p = do
   s <- gets substitution
   -- Checking if some extension exists for the given qualifier and getting the
   -- first to match.
-
-  let cenv' = sortBy (\c1 c2 -> compare (thd3 c2) (thd3 c1)) (getQuals cenv)
-
   p' <- liftIO $ applyQual s =<< compressQual p
-  x <- forM cenv' $ \(qvs, sch, _) -> do
+  x <- forM (getQuals cenv) $ \(qvs, sch) -> do
     sub <- Map.fromList <$> mapM (\c -> (c,) <$> fresh) qvs
     (a :=>: b, _) <- instantiateQual sub sch
     b' <- liftIO $ compressQual b
-    
+
     First <$> (fmap (a,b,) <$> matchMut' b' p') `tryOr` pure Nothing
 
   case getFirst $ mconcat x of
@@ -151,8 +148,8 @@ getDict (IsQVar t) = t
 createInstNames :: [PlumeType] -> Text
 createInstNames = List.foldl' (\acc x -> acc <> "_" <> createInstName x) ""
 
-getQuals :: ExtendEnv -> [([QuVar], Qualified PlumeQualifier, Integer)]
-getQuals (MkExtendEnv env) = map (\(a, MkInstance qs quals _ _ priority) -> (qs, a <$ quals, priority)) env
+getQuals :: ExtendEnv -> [([QuVar], Qualified PlumeQualifier)]
+getQuals (MkExtendEnv env) = map (\(a, MkInstance qs quals _ _) -> (qs, a <$ quals)) env
 
 unqualType :: Qualified PlumeType -> PlumeType
 unqualType (_ :=>: zs) = zs
diff --git a/src/Plume/TypeChecker/Monad/State.hs b/src/Plume/TypeChecker/Monad/State.hs
index 5e7f000..593a92f 100644
--- a/src/Plume/TypeChecker/Monad/State.hs
+++ b/src/Plume/TypeChecker/Monad/State.hs
@@ -69,13 +69,13 @@ newtype ExtendEnv = MkExtendEnv [(PlumeQualifier, Instance Typed.Expression ())]
 -- | (where the key is the method name and the value is the method expression),
 -- | and a map of types (where the key is the type name and the value is 
 -- | the type).
-data Instance val a = MkInstance [QuVar] (Qualified a) (Map Text val) (Map Text PlumeScheme) Integer
+data Instance val a = MkInstance [QuVar] (Qualified a) (Map Text val) (Map Text PlumeScheme)
   deriving (Eq, Show)
 
 -- | Instancing the Functor typeclass for the Instance type, in order to
 -- | be able to apply `void` function to the Instance type.
 instance Functor (Instance val) where
-  fmap f (MkInstance qs q m t p) = MkInstance qs (fmap f q) m t p
+  fmap f (MkInstance qs q m t) = MkInstance qs (fmap f q) m t
 
 -- | Empty state
 -- | The empty state is the initial state of the type checker
diff --git a/src/Plume/TypeChecker/Monad/Type.hs b/src/Plume/TypeChecker/Monad/Type.hs
index 6ca06b3..8d4c624 100644
--- a/src/Plume/TypeChecker/Monad/Type.hs
+++ b/src/Plume/TypeChecker/Monad/Type.hs
@@ -78,7 +78,7 @@ pattern TList t = TypeApp (TypeId "list") [t]
 pattern TInt, TBool, TString, TChar, TFloat, TUnit :: PlumeType
 pattern TInt = TypeId "int"
 pattern TBool = TypeId "bool"
-pattern TString = TList TChar
+pattern TString = TypeId "str"
 pattern TChar = TypeId "char"
 pattern TFloat = TypeId "float"
 pattern TUnit = TypeId "unit"