diff --git a/examples/poke_api/analysis_options.yaml b/examples/poke_api/analysis_options.yaml
new file mode 100644
index 0000000..d875ed0
--- /dev/null
+++ b/examples/poke_api/analysis_options.yaml
@@ -0,0 +1,11 @@
+include: package:lints/recommended.yaml
+
+linter:
+  rules:
+    annotate_overrides: true
+
+analyzer:
+  language:
+    strict-casts: true
+    strict-inference: true
+    strict-raw-types: true
diff --git a/examples/poke_api/lib/main.dart b/examples/poke_api/lib/main.dart
index 546b055..43657e9 100644
--- a/examples/poke_api/lib/main.dart
+++ b/examples/poke_api/lib/main.dart
@@ -1,47 +1,59 @@
 import 'dart:convert';
 
 import 'package:fpdart/fpdart.dart';
+import 'package:http/http.dart' as http;
 import 'package:poke_api/constants.dart';
 import 'package:poke_api/pokemon.dart';
 import 'package:poke_api/pokemon_error.dart';
 
 abstract interface class HttpClient {
-  String get(Uri uri);
+  Effect<void, PokemonError, String> get(Uri uri);
 }
 
-Effect<(HttpClient, JsonCodec), PokemonError, Pokemon> program(
+class Http implements HttpClient {
+  @override
+  Effect<void, PokemonError, String> get(Uri uri) => Effect.gen(
+        ($) async {
+          final response = await $.async(Effect.tryCatch(
+            execute: () => http.get(uri),
+            onError: (error, stackTrace) => const GetPokemonRequestError(),
+          ));
+
+          return response.body;
+        },
+      );
+}
+
+typedef Env = (HttpClient, JsonCodec);
+
+Effect<Env, PokemonError, Pokemon> program(
   String pokemonId,
 ) =>
     Effect.gen(($) async {
       final (client, json) = $.sync(Effect.env());
 
-      final id = $.sync(
-        Either.fromNullable(
-          int.tryParse(pokemonId),
-          PokemonIdNotInt.new,
-        ),
-      );
+      final id = $.sync(Either.fromNullable(
+        int.tryParse(pokemonId),
+        PokemonIdNotInt.new,
+      ).provide());
 
       if (id < Constants.minimumPokemonId && id > Constants.maximumPokemonId) {
         return $.sync(Effect.fail(const InvalidPokemonIdRange()));
       }
 
       final uri = Uri.parse(Constants.requestAPIUrl(id));
-      final body = await $.async(Effect.tryCatch(
-        execute: () => client.get(uri),
-        onError: (_, __) => const GetPokemonRequestError(),
-      ));
+      final body = await $.async(client.get(uri).provideVoid());
 
       final bodyJson = $.sync(Either.tryCatch(
         execute: () => json.decode(body),
         onError: (_, __) => const PokemonJsonDecodeError(),
-      ));
+      ).provide());
 
       final bodyJsonMap = $.sync<Map<String, dynamic>>(
-        Either.safeCastStrict(
+        Either.safeCastStrict<PokemonError, Map<String, dynamic>, dynamic>(
           bodyJson,
           (value) => const PokemonJsonInvalidMap(),
-        ),
+        ).provide(),
       );
 
       return $.sync(Effect.tryCatch(
@@ -49,3 +61,14 @@ Effect<(HttpClient, JsonCodec), PokemonError, Pokemon> program(
         onError: (_, __) => const PokemonInvalidJsonModel(),
       ));
     });
+
+void main() async {
+  await program("721")
+      .map((pokemon) => print(pokemon))
+      .catchError(
+        (error) => Effect.function(
+          () => print("No pokemon: $error"),
+        ),
+      )
+      .runFuture((Http(), JsonCodec()));
+}
diff --git a/examples/poke_api/lib/pokemon.dart b/examples/poke_api/lib/pokemon.dart
index 34409b1..6008654 100644
--- a/examples/poke_api/lib/pokemon.dart
+++ b/examples/poke_api/lib/pokemon.dart
@@ -17,4 +17,9 @@ class Pokemon {
         height: json['height'] as int,
         weight: json['weight'] as int,
       );
+
+  @override
+  String toString() {
+    return "Pokemon(id:$id, name:$name, height:$height, weight:$weight)";
+  }
 }
diff --git a/examples/poke_api/pubspec.yaml b/examples/poke_api/pubspec.yaml
index 423285d..1988048 100644
--- a/examples/poke_api/pubspec.yaml
+++ b/examples/poke_api/pubspec.yaml
@@ -10,6 +10,7 @@ environment:
   sdk: ">=3.3.0 <4.0.0"
 
 dependencies:
+  http: ^1.2.1
   fpdart:
     path: ../../packages/fpdart
 
diff --git a/packages/fpdart/lib/src/effect.dart b/packages/fpdart/lib/src/effect.dart
index 221c589..9e274fd 100644
--- a/packages/fpdart/lib/src/effect.dart
+++ b/packages/fpdart/lib/src/effect.dart
@@ -425,3 +425,8 @@ extension ProvideNever<L, R> on Effect<Never, L, R> {
   /// {@category execution}
   Future<Exit<L, R>> runFutureExitNoEnv() async => _unsafeRun(null);
 }
+
+extension ProvideVoid<L, R> on Effect<void, L, R> {
+  /// {@category execution}
+  Effect<V, L, R> provideVoid<V>() => provide((env) {});
+}
diff --git a/packages/fpdart/lib/src/either.dart b/packages/fpdart/lib/src/either.dart
index 5841e66..d3b1892 100644
--- a/packages/fpdart/lib/src/either.dart
+++ b/packages/fpdart/lib/src/either.dart
@@ -1,6 +1,6 @@
 part of "effect.dart";
 
-sealed class Either<L, R> extends IEffect<Never, L, R> {
+sealed class Either<L, R> extends IEffect<Null, L, R> {
   const Either();
 
   /// If calling `predicate` with `r` returns `true`, then return `Right(r)`.
diff --git a/packages/fpdart/lib/src/extension/future_or_extension.dart b/packages/fpdart/lib/src/extension/future_or_extension.dart
index 578a99b..eade6c6 100644
--- a/packages/fpdart/lib/src/extension/future_or_extension.dart
+++ b/packages/fpdart/lib/src/extension/future_or_extension.dart
@@ -1,11 +1,8 @@
 import 'dart:async';
 
 extension FutureOrThenExtension<A> on FutureOr<A> {
-  FutureOr<B> then<B>(FutureOr<B> Function(A a) f) {
-    if (this is Future) {
-      return (this as Future<A>).then(f);
-    }
-
-    return f(this as A);
-  }
+  FutureOr<B> then<B>(FutureOr<B> Function(A a) f) => switch (this) {
+        final Future<A> self => self.then(f),
+        final A self => f(self),
+      };
 }