diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..00a51af
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,6 @@
+#
+# https://help.github.com/articles/dealing-with-line-endings/
+#
+# These are explicitly windows files and should use crlf
+*.bat           text eol=crlf
+
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..1b6985c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+# Ignore Gradle project-specific cache directory
+.gradle
+
+# Ignore Gradle build output directory
+build
diff --git a/gradle/wrapper/gradle-wrapper.jar b/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000..41d9927
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.jar
Binary files differ
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 0000000..aa991fc
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.4.2-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/gradlew b/gradlew
new file mode 100755
index 0000000..1b6c787
--- /dev/null
+++ b/gradlew
@@ -0,0 +1,234 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+APP_NAME="Gradle"
+APP_BASE_NAME=${0##*/}
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"
diff --git a/gradlew.bat b/gradlew.bat
new file mode 100644
index 0000000..107acd3
--- /dev/null
+++ b/gradlew.bat
@@ -0,0 +1,89 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/lib/build.gradle b/lib/build.gradle
new file mode 100644
index 0000000..3f39f6b
--- /dev/null
+++ b/lib/build.gradle
@@ -0,0 +1,39 @@
+
+plugins {
+    id 'java-library'
+}
+
+repositories {
+    mavenLocal()
+    mavenCentral()
+}
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(17)
+    }
+}
+
+compileJava {
+    options.compilerArgs << '-Xlint:unchecked'
+    options.compilerArgs << '-Xlint:rawtypes'
+    options.release = 17
+}
+
+compileTestJava {
+    options.compilerArgs << '-Xlint:unchecked'
+    options.compilerArgs << '-Xlint:rawtypes'
+    options.release = 17
+}
+
+dependencies {
+    api 'io.vavr:vavr:0.10.4'
+
+    testImplementation 'org.junit.jupiter:junit-jupiter:5.8.1'
+    testImplementation("org.mockito:mockito-core:4.5.1")
+    testImplementation("org.mockito:mockito-junit-jupiter:4.5.1")
+}
+
+tasks.named('test') {
+    useJUnitPlatform()
+}
\ No newline at end of file
diff --git a/lib/src/main/java/com/github/tonivade/vavr/effect/Fiber.java b/lib/src/main/java/com/github/tonivade/vavr/effect/Fiber.java
new file mode 100644
index 0000000..4270cab
--- /dev/null
+++ b/lib/src/main/java/com/github/tonivade/vavr/effect/Fiber.java
@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2018-2021, Antonio Gabriel Muñoz Conejo <antoniogmc at gmail dot com>
+ * Distributed under the terms of the MIT License
+ */
+package com.github.tonivade.vavr.effect;
+
+public interface Fiber<T> {
+
+  IO<T> join();
+  
+  IO<Unit> cancel();
+  
+  static <T> Fiber<T> of(IO<T> join, IO<Unit> cancel) {
+    return new Fiber<T>() {
+      @Override
+      public IO<T> join() {
+        return join;
+      }
+      @Override
+      public IO<Unit> cancel() {
+        return cancel;
+      }
+    };
+  }
+}
\ No newline at end of file
diff --git a/lib/src/main/java/com/github/tonivade/vavr/effect/IO.java b/lib/src/main/java/com/github/tonivade/vavr/effect/IO.java
new file mode 100644
index 0000000..ce9ad3c
--- /dev/null
+++ b/lib/src/main/java/com/github/tonivade/vavr/effect/IO.java
@@ -0,0 +1,880 @@
+/*
+ * Copyright (c) 2018-2021, Antonio Gabriel Muñoz Conejo <antoniogmc at gmail dot com>
+ * Distributed under the terms of the MIT License
+ */
+package com.github.tonivade.vavr.effect;
+
+import static io.vavr.Function1.identity;
+import java.time.Duration;
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.NoSuchElementException;
+import java.util.Objects;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+import java.util.function.Supplier;
+import java.util.function.UnaryOperator;
+import io.vavr.CheckedConsumer;
+import io.vavr.CheckedRunnable;
+import io.vavr.Function1;
+import io.vavr.Function2;
+import io.vavr.PartialFunction;
+import io.vavr.Tuple;
+import io.vavr.Tuple2;
+import io.vavr.collection.HashMap;
+import io.vavr.collection.List;
+import io.vavr.collection.Seq;
+import io.vavr.concurrent.Future;
+import io.vavr.concurrent.Promise;
+import io.vavr.control.Either;
+import io.vavr.control.Option;
+import io.vavr.control.Try;
+
+public sealed interface IO<T> {
+
+  IO<Unit> UNIT = pure(Unit.unit());
+
+  default Future<T> runAsync() {
+    return runAsync(this, IOConnection.UNCANCELLABLE).future();
+  }
+
+  default Future<T> runAsync(Executor executor) {
+    return forked(executor).andThen(this).runAsync();
+  }
+  
+  default T unsafeRunSync() {
+    return safeRunSync().get();
+  }
+
+  default Try<T> safeRunSync() {
+    return runAsync().toTry();
+  }
+
+  default void safeRunAsync(Consumer<? super Try<? extends T>> callback) {
+    safeRunAsync(Future.DEFAULT_EXECUTOR, callback);
+  }
+
+  default void safeRunAsync(Executor executor, Consumer<? super Try<? extends T>> callback) {
+    runAsync(executor).onComplete(callback);
+  }
+
+  default <R> IO<R> map(Function1<? super T, ? extends R> map) {
+    return flatMap(map.andThen(IO::pure));
+  }
+
+  default <R> IO<R> flatMap(Function1<? super T, ? extends IO<? extends R>> map) {
+    return new FlatMapped<>(this, map.andThen(IO::narrowK));
+  }
+
+  default <R> IO<R> andThen(IO<? extends R> after) {
+    return flatMap(ignore -> after);
+  }
+
+  default <R> IO<R> ap(IO<Function1<? super T, ? extends R>> apply) {
+    return parMap2(Future.DEFAULT_EXECUTOR, this, apply, (v, a) -> a.apply(v));
+  }
+
+  default IO<Try<T>> attempt() {
+    return map(Try::success).recover(Try::failure);
+  }
+
+  default IO<Either<Throwable, T>> either() {
+    return attempt().map(Try::toEither);
+  }
+
+  default <L, R> IO<Either<L, R>> either(Function1<? super Throwable, ? extends L> mapError,
+                                         Function1<? super T, ? extends R> mapper) {
+    return either().map(either -> either.bimap(mapError, mapper));
+  }
+
+  default <R> IO<R> redeem(Function1<? super Throwable, ? extends R> mapError,
+                           Function1<? super T, ? extends R> mapper) {
+    return attempt().map(result -> result.fold(mapError, mapper));
+  }
+
+  default <R> IO<R> redeemWith(Function1<? super Throwable, IO<? extends R>> mapError,
+                               Function1<? super T, IO<? extends R>> mapper) {
+    return attempt().flatMap(result -> result.fold(mapError, mapper));
+  }
+
+  default IO<T> recover(Function1<? super Throwable, ? extends T> mapError) {
+    return recoverWith(partialFunction(x -> true, mapError.andThen(IO::pure)));
+  }
+
+  @SuppressWarnings("unchecked")
+  default <X extends Throwable> IO<T> recover(Class<X> type, Function1<? super X, ? extends T> function) {
+    return recoverWith(partialFunction(error -> error.getClass().equals(type), t -> function.andThen(IO::pure).apply((X) t)));
+  }
+  
+  @SuppressWarnings("serial")
+  static <A, B> PartialFunction<A, B> partialFunction(Predicate<? super A> matcher, Function1<? super A, ? extends B> function) {
+    return new PartialFunction<>() {
+      
+      @Override
+      public boolean isDefinedAt(A value) {
+        return matcher.test(value);
+      }
+      
+      @Override
+      public B apply(A t) {
+        return function.apply(t);
+      }
+    };
+  }
+
+  default IO<T> recoverWith(PartialFunction<? super Throwable, IO<? extends T>> mapper) {
+    return new Recover<>(this, mapper);
+  }
+
+  default IO<Tuple2<Duration, T>> timed() {
+    return IO.task(System::nanoTime).flatMap(
+      start -> map(result -> Tuple.of(Duration.ofNanos(System.nanoTime() - start), result)));
+  }
+  
+  default IO<Fiber<T>> fork() {
+    return async(callback -> {
+      IOConnection connection = IOConnection.cancellable();
+      Promise<T> promise = runAsync(this, connection);
+      
+      IO<T> join = fromFuture(promise.future());
+      IO<Unit> cancel = exec(connection::cancel);
+      
+      callback.accept(Try.success(Fiber.of(join, cancel)));
+    });
+  }
+
+  default IO<T> timeout(Duration duration) {
+    return timeout(Future.DEFAULT_EXECUTOR, duration);
+  }
+  
+  default IO<T> timeout(Executor executor, Duration duration) {
+    return racePair(executor, this, sleep(duration)).flatMap(either -> either.fold(
+        ta -> ta._2().cancel().map(x -> ta._1()),
+        tb -> tb._1().cancel().flatMap(x -> IO.raiseError(new TimeoutException()))));
+  }
+
+  default IO<T> repeat() {
+    return repeat(1);
+  }
+
+  default IO<T> repeat(int times) {
+    return repeat(this, unit(), times);
+  }
+
+  default IO<T> repeat(Duration delay) {
+    return repeat(delay, 1);
+  }
+
+  default IO<T> repeat(Duration delay, int times) {
+    return repeat(this, sleep(delay), times);
+  }
+
+  default IO<T> retry() {
+    return retry(1);
+  }
+
+  default IO<T> retry(int maxRetries) {
+    return retry(this, unit(), maxRetries);
+  }
+
+  default IO<T> retry(Duration delay) {
+    return retry(delay, 1);
+  }
+
+  default IO<T> retry(Duration delay, int maxRetries) {
+    return retry(this, sleep(delay), maxRetries);
+  }
+
+  @SuppressWarnings("unchecked")
+  static <T> IO<T> narrowK(IO<? extends T> value) {
+    return (IO<T>) value;
+  }
+
+  static <T> IO<T> pure(T value) {
+    return new Pure<>(value);
+  }
+  
+  static <A, B> IO<Either<A, B>> race(IO<? extends A> fa, IO<? extends B> fb) {
+    return race(Future.DEFAULT_EXECUTOR, fa, fb);
+  }
+  
+  static <A, B> IO<Either<A, B>> race(Executor executor, IO<? extends A> fa, IO<? extends B> fb) {
+    return racePair(executor, fa, fb).flatMap(either -> either.fold(
+        ta -> ta._2().cancel().map(x -> Either.left(ta._1())),
+        tb -> tb._1().cancel().map(x -> Either.right(tb._2()))));
+  }
+  
+  static <A, B> IO<Either<Tuple2<A, Fiber<B>>, Tuple2<Fiber<A>, B>>> racePair(Executor executor, IO<? extends A> fa, IO<? extends B> fb) {
+    return cancellable(callback -> {
+      
+      IOConnection connection1 = IOConnection.cancellable();
+      IOConnection connection2 = IOConnection.cancellable();
+      
+      Promise<A> promiseA = runAsync(IO.forked(executor).andThen(fa), connection1);
+      Promise<B> promiseB = runAsync(IO.forked(executor).andThen(fb), connection2);
+
+      promiseA.future().onComplete(result -> callback.accept(
+          result.map(a -> Either.left(Tuple.of(a, Fiber.of(IO.fromFuture(promiseB.future()), IO.exec(connection2::cancel)))))));
+      promiseB.future().onComplete(result -> callback.accept(
+          result.map(b -> Either.right(Tuple.of(Fiber.of(IO.fromFuture(promiseA.future()), IO.exec(connection2::cancel)), b)))));
+
+      return IO.exec(() -> {
+        try {
+          connection1.cancel();
+        } finally {
+          connection2.cancel();
+        }
+      });
+    });
+  }
+
+  static <T> IO<T> raiseError(Throwable error) {
+    return new Failure<>(error);
+  }
+
+  static <T> IO<T> delay(Duration delay, Supplier<? extends T> lazy) {
+    return sleep(delay).andThen(task(lazy));
+  }
+
+  static <T> IO<T> suspend(Supplier<IO<? extends T>> lazy) {
+    return new Suspend<>(lazy);
+  }
+
+  static <T, R> Function1<T, IO<R>> lift(Function1<T, R> task) {
+    return task.andThen(IO::pure);
+  }
+
+  public static <A, B> Function1<A, IO<B>> liftOption(Function1<? super A, ? extends Option<? extends B>> function) {
+    return value -> fromOption(function.apply(value));
+  }
+
+  public static <A, B> Function1<A, IO<B>> liftTry(Function1<? super A, ? extends Try<? extends B>> function) {
+    return value -> fromTry(function.apply(value));
+  }
+
+  public static <A, B> Function1<A, IO<B>> liftEither(Function1<? super A, ? extends Either<Throwable, ? extends B>> function) {
+    return value -> fromEither(function.apply(value));
+  }
+
+  static <T> IO<T> fromOption(Option<? extends T> task) {
+    return fromEither(toEither(task));
+  }
+
+  static <T> IO<T> fromTry(Try<? extends T> task) {
+    return fromEither(task.toEither());
+  }
+
+  static <T> IO<T> fromEither(Either<Throwable, ? extends T> task) {
+    return task.fold(IO::raiseError, IO::pure);
+  }
+  
+  static <T> IO<T> fromFuture(Future<? extends T> promise) {
+    CheckedConsumer<Consumer<? super Try<? extends T>>> callback = promise::onComplete;
+    return async(callback);
+  }
+  
+  static <T> IO<T> fromCompletableFuture(CompletableFuture<? extends T> promise) {
+    return fromFuture(Future.fromCompletableFuture(promise));
+  }
+
+  static IO<Unit> sleep(Duration duration) {
+    return sleep(Future.DEFAULT_EXECUTOR, duration);
+  }
+
+  static IO<Unit> sleep(Executor executor, Duration duration) {
+    return cancellable(callback -> {
+      Future<Unit> sleep = FutureModule.sleep(executor,duration)
+        .onComplete(result -> callback.accept(Try.success(Unit.unit())));
+      return IO.exec(() -> sleep.cancel(true));
+    });
+  }
+
+  static IO<Unit> exec(CheckedRunnable task) {
+    return task(asSupplier(task));
+  }
+
+  static <T> IO<T> task(Supplier<? extends T> producer) {
+    return new Delay<>(producer);
+  }
+
+  static <T> IO<T> never() {
+    return async(callback -> {});
+  }
+  
+  static IO<Unit> forked() {
+    return forked(Future.DEFAULT_EXECUTOR);
+  }
+  
+  static IO<Unit> forked(Executor executor) {
+    return async(callback -> executor.execute(() -> callback.accept(Try.success(Unit.unit()))));
+  }
+
+  static <T> IO<T> async(CheckedConsumer<Consumer<? super Try<? extends T>>> callback) {
+    return cancellable(asFunction(callback));
+  }
+
+  static <T> IO<T> cancellable(Function1<Consumer<? super Try<? extends T>>, IO<Unit>> callback) {
+    return new Async<>(callback);
+  }
+
+  static <A, T> IO<Function1<A, IO<T>>> memoize(Function1<A, IO<T>> function) {
+    return memoize(Future.DEFAULT_EXECUTOR, function);
+  }
+
+  static <A, T> IO<Function1<A, IO<T>>> memoize(Executor executor, Function1<A, IO<T>> function) {
+    var ref = Ref.make(HashMap.<A, Promise<T>>empty());
+    return ref.map(r -> {
+      Function1<A, IO<IO<T>>> result = a -> r.modify(map -> map.get(a).fold(() -> {
+        Promise<T> promise = Promise.make();
+        function.apply(a).safeRunAsync(executor, promise::tryComplete);
+        return Tuple.of(IO.fromFuture(promise.future()), map.put(a, promise));
+      }, promise -> Tuple.of(IO.fromFuture(promise.future()), map)));
+      return result.andThen(io -> io.flatMap(identity()));
+    });
+  }
+
+  static IO<Unit> unit() {
+    return UNIT;
+  }
+
+  static <T, R> IO<R> bracket(IO<? extends T> acquire, 
+      Function1<? super T, ? extends IO<? extends R>> use, Function1<? super T, IO<Unit>> release) {
+    return cancellable(callback -> {
+      
+      IOConnection cancellable = IOConnection.cancellable();
+      
+      Promise<? extends T> promise = runAsync(acquire, cancellable);
+      
+      promise.future()
+        .onFailure(error -> callback.accept(Try.failure(error)))
+        .onSuccess(resource -> runAsync(use.andThen(IO::narrowK).apply(resource), cancellable).future()
+          .onComplete(result -> runAsync(release.andThen(IO::narrowK).apply(resource), cancellable).future()
+            .onComplete(ignore -> callback.accept(result))
+        ));
+      
+      return IO.exec(cancellable::cancel);
+    });
+  }
+
+  static <T, R> IO<R> bracket(IO<? extends T> acquire, 
+      Function1<? super T, ? extends IO<? extends R>> use, CheckedConsumer<? super T> release) {
+    return bracket(acquire, use, asFunction(release));
+  }
+
+  static <T extends AutoCloseable, R> IO<R> bracket(IO<? extends T> acquire, 
+      Function1<? super T, ? extends IO<? extends R>> use) {
+    return bracket(acquire, use, AutoCloseable::close);
+  }
+
+  static IO<Unit> sequence(Seq<IO<?>> sequence) {
+    IO<?> initial = IO.unit();
+    return sequence.foldLeft(initial, (IO<?> a, IO<?> b) -> a.andThen(b)).andThen(IO.unit());
+  }
+
+  static <A> IO<Seq<A>> traverse(Seq<IO<A>> sequence) {
+    return traverse(Future.DEFAULT_EXECUTOR, sequence);
+  }
+
+  static <A> IO<Seq<A>> traverse(Executor executor, Seq<IO<A>> sequence) {
+    return sequence.foldLeft(pure(List.empty()), 
+        (IO<Seq<A>> xs, IO<A> a) -> parMap2(executor, xs, a, Seq::append));
+  }
+
+  static <A, B, C> IO<C> parMap2(IO<? extends A> fa, IO<? extends B> fb,
+                              Function2<? super A, ? super B, ? extends C> mapper) {
+    return parMap2(Future.DEFAULT_EXECUTOR, fa, fb, mapper);
+  }
+
+  static <A, B, C> IO<C> parMap2(Executor executor, IO<? extends A> fa, IO<? extends B> fb,
+                              Function2<? super A, ? super B, ? extends C> mapper) {
+    return cancellable(callback -> {
+      
+      IOConnection connection1 = IOConnection.cancellable();
+      IOConnection connection2 = IOConnection.cancellable();
+      
+      Promise<A> promiseA = runAsync(IO.forked(executor).andThen(fa), connection1);
+      Promise<B> promiseB = runAsync(IO.forked(executor).andThen(fb), connection2);
+      
+      promiseA.future().onComplete(a -> promiseB.future().onComplete(b -> callback.accept(map2(a, b, mapper))));
+      
+      return IO.exec(() -> {
+        try {
+          connection1.cancel();
+        } finally {
+          connection2.cancel();
+        }
+      });
+    });
+  }
+
+  static <A, B> IO<Tuple2<A, B>> tuple(IO<? extends A> fa, IO<? extends B> fb) {
+    return tuple(Future.DEFAULT_EXECUTOR, fa, fb);
+  }
+
+  static <A, B> IO<Tuple2<A, B>> tuple(Executor executor, IO<? extends A> fa, IO<? extends B> fb) {
+    return parMap2(executor, fa, fb, Tuple::of);
+  }
+
+  private static <T> Promise<T> runAsync(IO<T> current, IOConnection connection) {
+    return runAsync(current, connection, new CallStack<>(), Promise.make());
+  }
+
+  private static <A, B, C> Try<? extends C> map2(Try<A> a, Try<B> b, Function2<? super A, ? super B, ? extends C> mapper) {
+    return a.flatMap(x -> b.map(y -> mapper.apply(x, y)));
+  }
+
+  private static <T> Either<Throwable, T> toEither(Option<? extends T> task) {
+    return task.fold(() -> Either.left(new NoSuchElementException()), Either::right);
+  }
+
+  private static Supplier<Unit> asSupplier(CheckedRunnable task) {
+    return () -> {
+      task.unchecked().run();
+      return Unit.unit();
+    };
+  }
+
+  private static <T> Function1<T, IO<Unit>> asFunction(CheckedConsumer<? super T> release) {
+    return t -> {
+      release.unchecked().accept(t);
+      return unit();
+    };
+  }
+
+  @SuppressWarnings("unchecked")
+  private static <T, U, V> Promise<T> runAsync(IO<T> current, IOConnection connection, CallStack<T> stack, Promise<T> promise) {
+    while (true) {
+      try {
+        current = unwrap(current, stack, identity());
+        
+        if (current instanceof Pure<T> pure) {
+          return promise.success(pure.value);
+        }
+        
+        if (current instanceof Async<T> async) {
+          return executeAsync(async, connection, promise);
+        }
+        
+        if (current instanceof FlatMapped) {
+          stack.push();
+
+          var flatMapped = (FlatMapped<U, T>) current;
+          IO<U> source = IO.narrowK(unwrap(flatMapped.current, stack, u -> u.flatMap(flatMapped.next)));
+          
+          if (source instanceof Async<U> async) {
+            Promise<U> nextPromise = Promise.make();
+            
+            nextPromise.future().andThen(tryU -> tryU.onFailure(promise::failure)
+                .onSuccess(u -> runAsync(IO.narrowK(flatMapped.next.apply(u)), connection, stack, promise)));
+            
+            executeAsync(async, connection, nextPromise);
+            
+            return promise;
+          }
+
+          if (source instanceof Pure<U> pure) {
+            Function1<? super U, IO<T>> andThen = flatMapped.next.andThen(IO::narrowK);
+            current = andThen.apply(pure.value);
+          } else if (source instanceof FlatMapped) {
+            FlatMapped<V, U> flatMapped2 = (FlatMapped<V, U>) source;
+            current = flatMapped2.current.flatMap(a -> flatMapped2.next.apply(a).flatMap(flatMapped.next));
+          }
+        } else {
+          stack.pop();
+        }
+      } catch (Throwable error) {
+        Option<IO<T>> result = stack.tryHandle(error);
+        
+        if (result.isDefined()) {
+          current = result.get();
+        } else {
+          return promise.failure(error);
+        }
+      }
+    }
+  }
+
+  private static <T, U> IO<T> unwrap(IO<T> current, CallStack<U> stack, Function1<IO<? extends T>, IO<? extends U>> next) {
+    while (true) {
+      if (current instanceof Failure<T> failure) {
+        return stack.sneakyThrow(failure.error);
+      } else if (current instanceof Recover<T> recover) {
+        stack.add(partialFunction(recover.mapper::isDefinedAt, recover.mapper.andThen(next)));
+        current = recover.current;
+      } else if (current instanceof Suspend<T> suspend) {
+        Supplier<IO<T>> andThen = () -> IO.narrowK(suspend.lazy.get());
+        current = andThen.get();
+      } else if (current instanceof Delay<T> delay) {
+        return IO.pure(delay.task.get());
+      } else if (current instanceof Pure) {
+        return current;
+      } else if (current instanceof FlatMapped) {
+        return current;
+      } else if (current instanceof Async) {
+        return current;
+      } else {
+        throw new IllegalStateException();
+      }
+    }
+  }
+
+  private static <T> Promise<T> executeAsync(Async<T> current, IOConnection connection, Promise<T> promise) {
+    if (connection.isCancellable() && !connection.updateState(StateIO::startingNow).isRunnable()) {
+      return promise.complete(Try.failure(new CancellationException()));
+    }
+    
+    connection.setCancelToken(current.callback.apply(promise::tryComplete));
+    
+    promise.future().andThen(x -> connection.setCancelToken(UNIT));
+    
+    if (connection.isCancellable() && connection.updateState(StateIO::notStartingNow).isCancellingNow()) {
+      connection.cancelNow();
+    }
+
+    return promise;
+  }
+
+  private static <T> IO<T> repeat(IO<T> self, IO<Unit> pause, int times) {
+    return self.redeemWith(IO::raiseError, value -> {
+      if (times > 0) {
+        return pause.andThen(repeat(self, pause, times - 1));
+      } else return IO.pure(value);
+    });
+  }
+
+  private static <T> IO<T> retry(IO<T> self, IO<Unit> pause, int maxRetries) {
+    return self.redeemWith(error -> {
+      if (maxRetries > 0) {
+        return pause.andThen(retry(self, pause.repeat(), maxRetries - 1));
+      } else return IO.raiseError(error);
+    }, IO::pure);
+  }
+
+  final class Pure<T> implements IO<T> {
+
+    private final T value;
+
+    private Pure(T value) {
+      this.value = Objects.requireNonNull(value);
+    }
+
+    @Override
+    public String toString() {
+      return "Pure(" + value + ")";
+    }
+  }
+
+  final class Failure<T> implements IO<T> {
+
+    private final Throwable error;
+
+    private Failure(Throwable error) {
+      this.error = Objects.requireNonNull(error);
+    }
+
+    @Override
+    public String toString() {
+      return "Failure(" + error + ")";
+    }
+  }
+
+  final class FlatMapped<T, R> implements IO<R> {
+
+    private final IO<? extends T> current;
+    private final Function1<? super T, ? extends IO<? extends R>> next;
+
+    private FlatMapped(IO<? extends T> current,
+                         Function1<? super T, ? extends IO<? extends R>> next) {
+      this.current = Objects.requireNonNull(current);
+      this.next = Objects.requireNonNull(next);
+    }
+
+    @Override
+    public String toString() {
+      return "FlatMapped(" + current + ", ?)";
+    }
+  }
+
+  final class Delay<T> implements IO<T> {
+
+    private final Supplier<? extends T> task;
+
+    private Delay(Supplier<? extends T> task) {
+      this.task = Objects.requireNonNull(task);
+    }
+
+    @Override
+    public String toString() {
+      return "Delay(?)";
+    }
+  }
+
+  final class Async<T> implements IO<T> {
+
+    private final Function1<Consumer<? super Try<? extends T>>, IO<Unit>> callback;
+
+    private Async(Function1<Consumer<? super Try<? extends T>>, IO<Unit>> callback) {
+      this.callback = Objects.requireNonNull(callback);
+    }
+
+    @Override
+    public String toString() {
+      return "Async(?)";
+    }
+  }
+
+  final class Suspend<T> implements IO<T> {
+
+    private final Supplier<? extends IO<? extends T>> lazy;
+
+    private Suspend(Supplier<? extends IO<? extends T>> lazy) {
+      this.lazy = Objects.requireNonNull(lazy);
+    }
+
+    @Override
+    public String toString() {
+      return "Suspend(?)";
+    }
+  }
+
+  final class Recover<T> implements IO<T> {
+
+    private final IO<T> current;
+    private final PartialFunction<? super Throwable, ? extends IO<? extends T>> mapper;
+
+    private Recover(IO<T> current, PartialFunction<? super Throwable, ? extends IO<? extends T>> mapper) {
+      this.current = Objects.requireNonNull(current);
+      this.mapper = Objects.requireNonNull(mapper);
+    }
+
+    @Override
+    public String toString() {
+      return "Recover(" + current + ", ?)";
+    }
+  }
+}
+
+interface IOConnection {
+  
+  IOConnection UNCANCELLABLE = new IOConnection() {
+    @Override
+    public boolean isCancellable() { return false; }
+
+    @Override
+    public void setCancelToken(IO<Unit> cancel) { }
+
+    @Override
+    public void cancelNow() { }
+
+    @Override
+    public void cancel() { }
+
+    @Override
+    public StateIO updateState(UnaryOperator<StateIO> update) { return StateIO.INITIAL; }
+  };
+  
+  boolean isCancellable();
+
+  void setCancelToken(IO<Unit> cancel);
+  
+  void cancelNow();
+  
+  void cancel();
+  
+  StateIO updateState(UnaryOperator<StateIO> update);
+  
+  static IOConnection cancellable() {
+    return new IOConnection() {
+      
+      private IO<Unit> cancelToken;
+      private final AtomicReference<StateIO> state = new AtomicReference<>(StateIO.INITIAL);
+      
+      @Override
+      public boolean isCancellable() { return true; }
+      
+      @Override
+      public void setCancelToken(IO<Unit> cancel) { this.cancelToken = Objects.requireNonNull(cancel); }
+      
+      @Override
+      public void cancelNow() { cancelToken.runAsync(); }
+      
+      @Override
+      public void cancel() {
+        if (state.getAndUpdate(StateIO::cancellingNow).isCancelable()) {
+          cancelNow();
+        
+          state.set(StateIO.CANCELLED);
+        }
+      }
+      
+      @Override
+      public StateIO updateState(UnaryOperator<StateIO> update) {
+        return state.updateAndGet(update::apply);
+      }
+    };
+  }
+}
+
+final class StateIO {
+  
+  public static final StateIO INITIAL = new StateIO(false, false, false);
+  public static final StateIO CANCELLED = new StateIO(true, false, false);
+  
+  private final boolean isCancelled;
+  private final boolean cancellingNow;
+  private final boolean startingNow;
+  
+  public StateIO(boolean isCancelled, boolean cancellingNow, boolean startingNow) {
+    this.isCancelled = isCancelled;
+    this.cancellingNow = cancellingNow;
+    this.startingNow = startingNow;
+  }
+  
+  public boolean isCancelled() {
+    return isCancelled;
+  }
+  
+  public boolean isCancellingNow() {
+    return cancellingNow;
+  }
+  
+  public boolean isStartingNow() {
+    return startingNow;
+  }
+  
+  public StateIO cancellingNow() {
+    return new StateIO(isCancelled, true, startingNow);
+  }
+  
+  public StateIO startingNow() {
+    return new StateIO(isCancelled, cancellingNow, true);
+  }
+  
+  public StateIO notStartingNow() {
+    return new StateIO(isCancelled, cancellingNow, false);
+  }
+  
+  public boolean isCancelable() {
+    return !isCancelled && !cancellingNow && !startingNow;
+  }
+  
+  public boolean isRunnable() {
+    return !isCancelled && !cancellingNow;
+  }
+}
+
+final class CallStack<T> {
+  
+  private StackItem<T> top = new StackItem<>();
+  
+  public void push() {
+    top.push();
+  }
+
+  public void pop() {
+    if (top.count() > 0) {
+      top.pop();
+    } else {
+      top = top.prev();
+    }
+  }
+  
+  public void add(PartialFunction<? super Throwable, ? extends IO<? extends T>> mapError) {
+    if (top.count() > 0) {
+      top.pop();
+      top = new StackItem<>(top);
+    }
+    top.add(mapError);
+  }
+  
+  public Option<IO<T>> tryHandle(Throwable error) {
+    while (top != null) {
+      top.reset();
+      Option<IO<T>> result = top.tryHandle(error);
+      
+      if (result.isDefined()) {
+        return result;
+      } else {
+        top = top.prev();
+      }
+    }
+    return Option.none();
+  }
+  
+  // XXX: https://www.baeldung.com/java-sneaky-throws
+  @SuppressWarnings("unchecked")
+  public <X extends Throwable, R> R sneakyThrow(Throwable t) throws X {
+    throw (X) t;
+  }
+}
+
+final class StackItem<T> {
+  
+  private int count = 0;
+  private final Deque<PartialFunction<? super Throwable, ? extends IO<? extends T>>> recover = new ArrayDeque<>();
+
+  private final StackItem<T> prev;
+
+  public StackItem() {
+    this(null);
+  }
+
+  public StackItem(StackItem<T> prev) {
+    this.prev = prev;
+  }
+  
+  public StackItem<T> prev() {
+    return prev;
+  }
+  
+  public int count() {
+    return count;
+  }
+  
+  public void push() {
+    count++;
+  }
+  
+  public void pop() {
+    count--;
+  }
+  
+  public void reset() {
+    count = 0;
+  }
+  
+  public void add(PartialFunction<? super Throwable, ? extends IO<? extends T>> mapError) {
+    recover.addFirst(mapError);
+  }
+
+  public Option<IO<T>> tryHandle(Throwable error) {
+    while (!recover.isEmpty()) {
+      var mapError = recover.removeFirst();
+      if (mapError.isDefinedAt(error)) {
+        return Option.some(mapError.andThen(IO::<T>narrowK).apply(error));
+      }
+    }
+    return Option.none();
+  }
+}
+
+interface FutureModule {
+
+  ScheduledExecutorService SCHEDULER = Executors.newScheduledThreadPool(0);
+
+  static Future<Unit> sleep(Executor executor, Duration delay) {
+    return Future.fromCompletableFuture(executor, CompletableFuture.supplyAsync(Unit::unit, delayedExecutor(delay, executor)));
+  }
+
+  static Executor delayedExecutor(Duration delay, Executor executor) {
+    return task -> SCHEDULER.schedule(() -> executor.execute(task), delay.toMillis(), TimeUnit.MILLISECONDS);
+  }
+}
\ No newline at end of file
diff --git a/lib/src/main/java/com/github/tonivade/vavr/effect/Ref.java b/lib/src/main/java/com/github/tonivade/vavr/effect/Ref.java
new file mode 100644
index 0000000..175ece3
--- /dev/null
+++ b/lib/src/main/java/com/github/tonivade/vavr/effect/Ref.java
@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2018-2021, Antonio Gabriel Muñoz Conejo <antoniogmc at gmail dot com>
+ * Distributed under the terms of the MIT License
+ */
+package com.github.tonivade.vavr.effect;
+
+import java.util.Objects;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.UnaryOperator;
+
+import io.vavr.Function1;
+import io.vavr.Tuple2;
+
+public final class Ref<A> {
+
+  private final AtomicReference<A> value;
+
+  private Ref(AtomicReference<A> value) {
+    this.value = Objects.requireNonNull(value);
+  }
+
+  public IO<A> get() {
+    return IO.task(value::get);
+  }
+
+  public IO<Unit> set(A newValue) {
+    return IO.task(() -> { value.set(newValue); return Unit.unit(); });
+  }
+  
+  public <B> IO<B> modify(Function1<A, Tuple2<B, A>> change) {
+    return IO.task(() -> {
+      var loop = true;
+      B result = null;
+      while (loop) {
+        A current = value.get();
+        var tuple = change.apply(current);
+        result = tuple._1();
+        loop = !value.compareAndSet(current, tuple._2());
+      }
+      return result;
+    });
+  }
+
+  public IO<Unit> lazySet(A newValue) {
+    return IO.task(() -> { value.lazySet(newValue); return Unit.unit(); });
+  }
+
+  public IO<A> getAndSet(A newValue) {
+    return IO.task(() -> value.getAndSet(newValue));
+  }
+
+  public IO<A> updateAndGet(UnaryOperator<A> update) {
+    return IO.task(() -> value.updateAndGet(update::apply));
+  }
+
+  public IO<A> getAndUpdate(UnaryOperator<A> update) {
+    return IO.task(() -> value.getAndUpdate(update::apply));
+  }
+  
+  public static <A> IO<Ref<A>> make(A value) {
+    return IO.pure(of(value));
+  }
+
+  public static <A> Ref<A> of(A value) {
+    return new Ref<>(new AtomicReference<>(value));
+  }
+
+  @Override
+  public String toString() {
+    return String.format("Ref(%s)", value.get());
+  }
+}
diff --git a/lib/src/main/java/com/github/tonivade/vavr/effect/Unit.java b/lib/src/main/java/com/github/tonivade/vavr/effect/Unit.java
new file mode 100644
index 0000000..0f7c8c6
--- /dev/null
+++ b/lib/src/main/java/com/github/tonivade/vavr/effect/Unit.java
@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2018-2021, Antonio Gabriel Muñoz Conejo <antoniogmc at gmail dot com>
+ * Distributed under the terms of the MIT License
+ */
+package com.github.tonivade.vavr.effect;
+
+import java.io.Serial;
+import java.io.Serializable;
+
+/**
+ * Type that represents a single value called Unit.
+ */
+public final class Unit implements Serializable {
+
+  @Serial
+  private static final long serialVersionUID = -8253613036328680583L;
+
+  private static final Unit INSTANCE = new Unit();
+
+  private Unit() {}
+
+  public static Unit unit() {
+    return INSTANCE;
+  }
+
+  @Override
+  public String toString() {
+    return "Unit";
+  }
+  
+  @Serial
+  private Object readResolve() {
+    return INSTANCE;
+  }
+}
diff --git a/lib/src/test/java/com/github/tonivade/vavr/effect/IOTest.java b/lib/src/test/java/com/github/tonivade/vavr/effect/IOTest.java
new file mode 100644
index 0000000..94f0931
--- /dev/null
+++ b/lib/src/test/java/com/github/tonivade/vavr/effect/IOTest.java
@@ -0,0 +1,394 @@
+/*
+ * Copyright (c) 2018-2021, Antonio Gabriel Muñoz Conejo <antoniogmc at gmail dot com>
+ * Distributed under the terms of the MIT License
+ */
+package com.github.tonivade.vavr.effect;
+
+import static org.junit.jupiter.api.Assertions.assertAll;
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.timeout;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.time.Duration;
+import java.util.NoSuchElementException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import io.vavr.CheckedFunction1;
+import io.vavr.Function1;
+import io.vavr.Tuple2;
+import io.vavr.collection.List;
+import io.vavr.collection.Seq;
+import io.vavr.concurrent.Future;
+import io.vavr.control.Either;
+import io.vavr.control.Try;
+
+@ExtendWith(MockitoExtension.class)
+public class IOTest {
+
+  @Test
+  public void pure() {
+    IO<String> pure = IO.pure("hola mundo");
+
+    assertAll(
+        () -> assertEquals("hola mundo", pure.unsafeRunSync()),
+        () -> assertEquals("HOLA MUNDO", pure.map(String::toUpperCase).unsafeRunSync()),
+        () -> assertArrayEquals(new String[] { "hola", "mundo" },
+            pure.flatMap(string -> IO.task(() -> string.split(" "))).unsafeRunSync()),
+        () -> assertEquals(Integer.valueOf(100), pure.andThen(IO.task(() -> 100)).unsafeRunSync()));
+  }
+  
+  @Test
+  public void asyncSuccess() {
+    IO<String> async = IO.async(callback -> {
+      System.out.println(Thread.currentThread().getName());
+      Thread.sleep(100);
+      callback.accept(Try.success("1"));
+    });
+    
+    Future<String> foldMap = IO.forked().andThen(async).runAsync();
+    
+    assertEquals("1", foldMap.get());
+  }
+  
+  @Test
+  public void asyncFailure() {
+    IO<String> async = IO.async(callback -> {
+      Thread.sleep(100);
+      callback.accept(Try.failure(new UnsupportedOperationException()));
+    });
+    
+    Future<String> foldMap = IO.forked().andThen(async).runAsync();
+   
+    assertThrows(UnsupportedOperationException.class, foldMap::get);
+  }
+
+//  @Test
+//  public void echo() {
+//    IO<Unit> echo = narrowK(console.println("write your name"))
+//        .andThen(narrowK(console.readln()))
+//        .flatMap(name -> narrowK(console.println("Hello " + name)))
+//        .andThen(narrowK(console.println("end")));
+//
+//    ConsoleExecutor executor = new ConsoleExecutor().read("Toni");
+//
+//    executor.run(echo);
+//
+//    assertEquals("write your name\nHello Toni\nend\n", executor.getOutput());
+//  }
+
+  @Test
+  public void safeRunAsync() {
+    IO<List<String>> program = currentThreadIO();
+
+    Try<List<String>> result = program.runAsync().await(1, TimeUnit.SECONDS).toTry();
+
+    assertEquals(Try.success(5), result.map(List::size));
+  }
+
+  @Test
+  public void bracket() throws SQLException {
+    ResultSet resultSet = mock(ResultSet.class);
+    when(resultSet.getString("id")).thenReturn("value");
+
+    IO<String> bracket = IO.bracket(open(resultSet), IO.liftTry(tryGetString("id")));
+
+    assertEquals("value", bracket.unsafeRunSync());
+    verify(resultSet).close();
+  }
+
+  @Test
+  public void safeRunAsyncSuccess(@Mock Consumer<? super Try<? extends String>> callback) {
+    IO.pure("hola").safeRunAsync(callback);
+
+    verify(callback, timeout(1000)).accept(Try.success("hola"));
+  }
+
+  @Test
+  public void unsafeRunAsyncFailure(@Mock Consumer<? super Try<? extends String>> callback) {
+    RuntimeException error = new RuntimeException();
+
+    IO.<String>raiseError(error).safeRunAsync(callback);
+
+    verify(callback, timeout(1000)).accept(Try.failure(error));
+  }
+
+  @Test
+  public void recover() {
+    IO<String> recover = IO.<String>raiseError(new RuntimeException()).recover(error -> "hola mundo");
+
+    assertEquals("hola mundo", recover.unsafeRunSync());
+  }
+
+  @Test
+  public void recoverWith() {
+    IO<String> recover = IO.<String>raiseError(new IllegalArgumentException())
+        .recover(IllegalArgumentException.class, error -> "hola mundo");
+
+    assertEquals("hola mundo", recover.unsafeRunSync());
+  }
+
+  @Test
+  public void recoverWithNotMatch() {
+    IO<String> recover = IO.<String>raiseError(new IllegalArgumentException())
+        .recover(NoSuchElementException.class, error -> "hola mundo");
+
+    assertThrows(IllegalArgumentException.class, recover::unsafeRunSync);
+  }
+
+  @Test
+  public void retry(@Mock Supplier<String> computation) {
+    when(computation.get()).thenThrow(UnsupportedOperationException.class);
+
+    Try<String> retry = IO.task(computation).retry().safeRunSync();
+
+    assertTrue(retry.isFailure());
+    verify(computation, times(2)).get();
+  }
+
+  @Test
+  public void retryFailure(@Mock Supplier<String> computation) {
+    when(computation.get()).thenThrow(UnsupportedOperationException.class);
+
+    Try<String> retry = IO.task(computation).retry(Duration.ofMillis(100), 3).safeRunSync();
+
+    assertTrue(retry.isFailure());
+    verify(computation, times(4)).get();
+  }
+
+  @Test
+  public void retrySuccess(@Mock Supplier<String> computation) {
+    when(computation.get())
+        .thenThrow(UnsupportedOperationException.class)
+        .thenThrow(UnsupportedOperationException.class)
+        .thenThrow(UnsupportedOperationException.class)
+        .thenReturn("hola");
+
+    Try<String> retry = IO.task(computation).retry(Duration.ofMillis(100), 3).safeRunSync();
+
+    assertEquals("hola", retry.get());
+    verify(computation, times(4)).get();
+  }
+
+  @Test
+  public void repeatSuccess(@Mock Supplier<String> computation) {
+    when(computation.get()).thenReturn("hola");
+
+    Try<String> repeat = IO.task(computation).repeat(Duration.ofMillis(100), 3).safeRunSync();
+
+    assertEquals("hola", repeat.get());
+    verify(computation, times(4)).get();
+  }
+
+  @Test
+  public void repeatFailure(@Mock Supplier<String> computation) {
+    when(computation.get()).thenReturn("hola").thenThrow(UnsupportedOperationException.class);
+
+    Try<String> repeat = IO.task(computation).repeat(Duration.ofMillis(100), 3).safeRunSync();
+
+    assertTrue(repeat.isFailure());
+    verify(computation, times(2)).get();
+  }
+
+  @Test
+  public void repeat(@Mock Supplier<String> computation) {
+    when(computation.get()).thenReturn("hola");
+
+    Try<String> repeat = IO.task(computation).repeat().safeRunSync();
+
+    assertEquals("hola", repeat.get());
+    verify(computation, times(2)).get();
+  }
+
+  @Test
+  public void flatMapped() {
+    IO<String> io = IO.unit()
+        .map(ignore -> "hola")
+        .map(ignore -> "hola")
+        .map(ignore -> "hola")
+        .map(ignore -> "adios");
+
+    assertEquals("adios", io.unsafeRunSync());
+  }
+
+  @Test
+  public void stackSafety() {
+    IO<Integer> sum = sum(100000, 0);
+
+    Future<Integer> futureSum = sum.runAsync();
+
+    assertEquals(705082704, sum.unsafeRunSync());
+    assertEquals(Try.success(705082704), futureSum.await(1, TimeUnit.SECONDS).toTry());
+  }
+
+  @Test
+  public void timed() {
+    IO<Tuple2<Duration, Integer>> sum = sum(100000, 0).timed();
+
+    Tuple2<Duration, Integer> result = sum.unsafeRunSync();
+
+    assertEquals(705082704, result._2());
+    assertTrue(result._1().toMillis() > 0);
+  }
+  
+  @Test
+  public void timeoutFail() {
+    assertThrows(TimeoutException.class, IO.never().timeout(Duration.ofSeconds(1))::unsafeRunSync);
+  }
+  
+  @Test
+  public void timeoutSuccess() {
+    assertEquals(1, IO.pure(1).timeout(Duration.ofSeconds(1)).unsafeRunSync());
+  }
+  
+  @Test
+  public void traverse() {
+    IO<String> left = IO.task(() -> "left");
+    IO<String> right = IO.task(() -> "right");
+    
+    IO<Seq<String>> traverse = IO.traverse(List.of(left, right));
+    
+    assertEquals(List.of("left", "right"), traverse.unsafeRunSync());
+  }
+
+  @Test
+  public void raceA() {
+    IO<Either<Integer, String>> race = IO.race(
+        IO.delay(Duration.ofMillis(10), () -> 10),
+        IO.delay(Duration.ofMillis(100), () -> "b"));
+    
+    Either<Integer, String> orElseThrow = race.unsafeRunSync();
+    
+    assertEquals(Either.left(10), orElseThrow);
+  }
+
+  @Test
+  public void raceB() {
+    IO<Either<Integer, String>> race = IO.race(
+        IO.delay(Duration.ofMillis(100), () -> 10),
+        IO.delay(Duration.ofMillis(10), () -> "b"));
+    
+    Either<Integer, String> orElseThrow = race.unsafeRunSync();
+    
+    assertEquals(Either.right("b"), orElseThrow);
+  }
+  
+  @Test
+  public void fork() {
+    IO<String> result = IO.pure("hola")
+      .flatMap(hello -> IO.delay(Duration.ofSeconds(1), () -> hello + " toni").fork())
+      .flatMap(Fiber::join);
+    
+    String orElseThrow = result.runAsync().get();
+
+    assertEquals("hola toni", orElseThrow);
+  }
+  
+  @Test
+  public void memoize(@Mock Function1<String, String> toUpperCase) {
+    when(toUpperCase.apply(any()))
+      .thenAnswer(args -> args.getArgument(0, String.class).toUpperCase());
+    
+    IO<Function1<String, IO<String>>> memoized = IO.memoize((String str) -> IO.pure(toUpperCase.apply(str)));
+    
+    IO<String> flatMap = memoized.flatMap(x -> x.apply("hola"));
+    flatMap.unsafeRunSync();
+    flatMap.unsafeRunSync();
+    flatMap.unsafeRunSync();
+    flatMap.unsafeRunSync();
+    
+    verify(toUpperCase).apply("hola");
+  }
+  
+  @Test
+  public void fibSyncTest() {
+    assertAll(
+        () -> assertEquals(1, fibSync(1).unsafeRunSync()),
+        () -> assertEquals(1, fibSync(2).unsafeRunSync()),
+        () -> assertEquals(2, fibSync(3).unsafeRunSync()),
+        () -> assertEquals(3, fibSync(4).unsafeRunSync()),
+        () -> assertEquals(5, fibSync(5).unsafeRunSync()),
+        () -> assertEquals(8, fibSync(6).unsafeRunSync()),
+        () -> assertEquals(13, fibSync(7).unsafeRunSync()),
+        () -> assertEquals(21, fibSync(8).unsafeRunSync()),
+        () -> assertEquals(55, fibSync(10).unsafeRunSync()),
+        () -> assertEquals(6765, fibSync(20).unsafeRunSync())
+        );
+  }
+  
+  @Test
+  public void fibAsyncTest() {
+    assertAll(
+        () -> assertEquals(1, fibAsync(1).unsafeRunSync()),
+        () -> assertEquals(1, fibAsync(2).unsafeRunSync()),
+        () -> assertEquals(2, fibAsync(3).unsafeRunSync()),
+        () -> assertEquals(3, fibAsync(4).unsafeRunSync()),
+        () -> assertEquals(5, fibAsync(5).unsafeRunSync()),
+        () -> assertEquals(8, fibAsync(6).unsafeRunSync()),
+        () -> assertEquals(13, fibAsync(7).unsafeRunSync()),
+        () -> assertEquals(21, fibAsync(8).unsafeRunSync()),
+        () -> assertEquals(55, fibAsync(10).unsafeRunSync()),
+        () -> assertEquals(6765, fibAsync(20).unsafeRunSync())
+        );
+  }
+
+  private IO<Integer> fibSync(int number) {
+    if (number < 2) {
+      return IO.pure(number);
+    }
+    var number1 = fibSync(number - 1);
+    var number2 = fibSync(number - 2);
+    return number1.flatMap(x -> number2.map(y -> x + y));
+  }
+
+  private IO<Integer> fibAsync(int number) {
+    if (number < 2) {
+      return IO.pure(number);
+    }
+    return IO.parMap2(fibAsync(number - 1), fibAsync(number - 2), Integer::sum);
+  }
+
+  private IO<ResultSet> open(ResultSet resultSet) {
+    return IO.pure(resultSet);
+  }
+
+  private Function1<ResultSet, Try<String>> tryGetString(String column) {
+    return rs -> Try.of(() -> getString(column).apply(rs));
+  }
+
+  private CheckedFunction1<ResultSet, String> getString(String column) {
+    return resultSet -> resultSet.getString(column);
+  }
+
+  private IO<Integer> sum(Integer n, Integer sum) {
+    if (n == 0) {
+      return IO.pure(sum);
+    }
+    return IO.suspend(() -> sum(n - 1, sum + n));
+  }
+
+  private IO<List<String>> currentThreadIO() {
+    Ref<List<String>> ref = Ref.of(List.empty());
+    IO<List<String>> currentThread =
+        ref.updateAndGet(list -> list.append(Thread.currentThread().getName()));
+
+    return currentThread
+        .andThen(currentThread
+            .andThen(currentThread
+                .andThen(currentThread
+                    .andThen(currentThread))));
+  }
+}
diff --git a/settings.gradle b/settings.gradle
new file mode 100644
index 0000000..6218084
--- /dev/null
+++ b/settings.gradle
@@ -0,0 +1,11 @@
+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * The settings file is used to specify which projects to include in your build.
+ *
+ * Detailed information about configuring a multi-project build in Gradle can be found
+ * in the user manual at https://docs.gradle.org/7.4.2/userguide/multi_project_builds.html
+ */
+
+rootProject.name = 'vavr-effect'
+include('lib')