diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -35,21 +35,15 @@
                  , '( "sumType1"
                     , Named "SumTypeWithCustomConstructorNames"
                         ( JsonEither
-                            ( JsonEither
-                                (Named "IntConstructor" JsonInt)
-                                (Named "StringConstructor" JsonString)
-                            )
-                            (Named "FloatConstructor" JsonNum)
+                           '[ Named "IntConstructor" JsonInt
+                            , Named "StringConstructor" JsonString
+                            , Named "FloatConstructor" JsonNum
+                            ]
                         )
                     )
                  , '( "sumType2"
                     , Named "SumTypeWithAutomaticConstructorNames"
-                        ( JsonEither
-                            ( JsonEither
-                                JsonInt
-                                JsonString
-                            )
-                            JsonNum
+                        ( JsonEither '[JsonInt, JsonString, JsonNum]
                         )
                     )
                  ]
diff --git a/json-spec-elm.cabal b/json-spec-elm.cabal
--- a/json-spec-elm.cabal
+++ b/json-spec-elm.cabal
@@ -1,6 +1,6 @@
 cabal-version:       3.0
 name:                json-spec-elm
-version:             0.4.0.7
+version:             0.5.0.1
 synopsis:            Elm code generate for `json-spec`.
 description:         
                      Produce elm types, encoders, and decoders from a
@@ -21,11 +21,11 @@
 
 common dependencies
   build-depends:
-    , base                 >= 4.17.2.1 && < 4.22
-    , containers           >= 0.6.7    && < 0.8
-    , elm-syntax           >= 0.3.2.0  && < 0.4
-    , json-spec            >= 0.3.0.0  && < 1.3
-    , text                 >= 2.0.2    && < 2.2
+    , base                 >= 4.19.2.0 && < 4.22
+    , containers           >= 0.6.8    && < 0.8
+    , elm-syntax           >= 0.3.3.0  && < 0.4
+    , json-spec            >= 1.3.0.0  && < 1.4
+    , text                 >= 2.1.1    && < 2.2
 
 common warnings
   ghc-options:
@@ -47,7 +47,7 @@
     -Wunused-packages
   build-depends:
     , bound                >= 2.0.7 && < 2.1
-    , mtl                  >= 2.2.2 && < 2.4
+    , mtl                  >= 2.3.1 && < 2.4
 
 flag compile-elm
   description:
@@ -67,7 +67,7 @@
       , directory            >= 1.3.7.1  && < 1.4
       , hspec                >= 2.11.1   && < 2.12
       , prettyprinter        >= 1.7.1    && < 1.8
-      , process              >= 1.6.16.0 && < 1.7
+      , process              >= 1.6.25.0 && < 1.7
       , unordered-containers >= 0.2.19.1 && < 0.3
   else
     type: exitcode-stdio-1.0
diff --git a/src/Data/JsonSpec/Elm.hs b/src/Data/JsonSpec/Elm.hs
--- a/src/Data/JsonSpec/Elm.hs
+++ b/src/Data/JsonSpec/Elm.hs
@@ -72,13 +72,11 @@
     The specification
 
     > Named "MySumType"
-    >   ( JsonEither
-    >       (Named "AnInt" JsonInt)
-    >       ( JsonEither
-    >           JsonFloat -- note the omitted name
-    >           ( Named "AString" JsonString)
-    >       )
-    >   )
+    >   ( JsonEither '[
+    >       Named "AnInt" JsonInt,
+    >       JsonFloat,  -- note the omitted name
+    >       Named "AString" JsonString
+    >   ])
 
     will produce the Elm type
 
@@ -439,10 +437,10 @@
     encoderOf = do
       defs @def
       encoderOf @(JsonLet more spec)
-instance {- HasType (JsonEither left right) -}
+instance {- HasType (JsonEither branches) -}
     (TypeError AnonSumTypeError)
   =>
-    HasType (JsonEither left right)
+    HasType (JsonEither branches)
   where
     typeOf = error "undefinable"
     decoderOf = error "undefinable"
@@ -468,25 +466,25 @@
 
 class HasDef (def :: (Symbol, Specification)) where
   defs :: Definitions ()
-instance {- HasDef '(name, JsonEither left right) -}
+instance {- HasDef '(name, JsonEither branches) -}
     ( KnownSymbol name
-    , SumDef (JsonEither left right)
+    , SumDef (JsonEither branches)
     )
   =>
-    HasDef '(name, JsonEither left right)
+    HasDef '(name, JsonEither branches)
   where
     defs = do
-        branches <- sumDef @(JsonEither left right)
+        branches_ <- sumDef @(JsonEither branches)
         let
           constructors :: [(Constructor, [Scope Int Type Void])]
           constructors =
             [ ( Name.Constructor (constructorName conName n)
               , [Scope type_]
               )
-            | (n, (conName, type_)) <- zip [1..] branches
+            | (n, (conName, type_)) <- zip [1..] branches_
             ]
-        decoders <- sumDecoders @(JsonEither left right)
-        encoders <- sumEncoders @(JsonEither left right)
+        decoders <- sumDecoders @(JsonEither branches)
+        encoders <- sumEncoders @(JsonEither branches)
         tell . Set.fromList $
           [ Def.Type (localName name) 0 constructors
           , Def.Constant
@@ -628,23 +626,27 @@
   sumDef :: forall v. Definitions [(Maybe Text, Type v)]
   sumDecoders :: Definitions [(Maybe Text, Expression Void)]
   sumEncoders :: Definitions [(Maybe Text, Expression Void)]
-instance {- SumDef (JsonEither left right) -}
-    (SumDef left, SumDef right)
+instance SumDef (JsonEither '[]) where
+  sumDef = pure []
+  sumDecoders = pure []
+  sumEncoders = pure []
+instance {- SumDef (JsonEither (a ': as)) -}
+    (SumDef a, SumDef (JsonEither as))
   =>
-    SumDef (JsonEither left right)
+    SumDef (JsonEither (a ': as))
   where
     sumDef = do
-      left <- sumDef @left
-      right <- sumDef @right
-      pure $ left ++ right
+      aDef <- sumDef @a
+      asDef <- sumDef @(JsonEither as)
+      pure $ aDef ++ asDef
     sumDecoders = do
-      left <- sumDecoders @left
-      right <- sumDecoders @right
-      pure (left ++ right)
+      aDec <- sumDecoders @a
+      asDec <- sumDecoders @(JsonEither as)
+      pure (aDec ++ asDec)
     sumEncoders = do
-      left <- sumEncoders @left
-      right <- sumEncoders @right
-      pure (left ++ right)
+      aEnc <- sumEncoders @a
+      asEnc <- sumEncoders @(JsonEither as)
+      pure (aEnc ++ asEnc)
 instance {- SumDef (JsonLet '[ '(name, def) ] (JsonRef name)) -}
     ( HasType def
     , KnownSymbol name
@@ -774,15 +776,7 @@
     :$$: Lits.Text ""
     :$$: Lits.Text "> JsonLet"
     :$$: Lits.Text ">   '[ '( \"MySum\""
-    :$$: Lits.Text ">       , JsonEither"
-    :$$: Lits.Text ">           ( JsonEither"
-    :$$: Lits.Text ">               JsonInt"
-    :$$: Lits.Text ">               JsonString"
-    :$$: Lits.Text ">           )"
-    :$$: Lits.Text ">           ( JsonEither"
-    :$$: Lits.Text ">               JsonFloat"
-    :$$: Lits.Text ">               JsonBool"
-    :$$: Lits.Text ">           )"
+    :$$: Lits.Text ">       , JsonEither '[JsonInt, JsonString, JsonFloat, JsonBool]"
     :$$: Lits.Text ">       )"
     :$$: Lits.Text ">    ]"
     :$$: Lits.Text ">    (JsonRef \"MySum\")"