diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index 263c9e0..026b0d4 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -17,6 +17,7 @@
             </intent-filter>
         </activity>
         <activity android:name=".option.OptionActivity" />
+        <activity android:name=".either.EitherActivity" />
     </application>
 
 </manifest>
\ No newline at end of file
diff --git a/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/MainActivity.kt b/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/MainActivity.kt
index e3abfcd..98a2c8d 100644
--- a/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/MainActivity.kt
+++ b/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/MainActivity.kt
@@ -3,6 +3,7 @@ package com.danielecampogiani.androidfunctionalvalidation
 import android.content.Intent
 import android.os.Bundle
 import android.support.v7.app.AppCompatActivity
+import com.danielecampogiani.androidfunctionalvalidation.either.EitherActivity
 import com.danielecampogiani.androidfunctionalvalidation.option.OptionActivity
 import kotlinx.android.synthetic.main.activity_main.*
 
@@ -13,7 +14,15 @@ class MainActivity : AppCompatActivity() {
         setContentView(R.layout.activity_main)
 
         option_button.setOnClickListener {
-            startActivity(Intent(this, OptionActivity::class.java))
+            start<OptionActivity>()
         }
+
+        either_button.setOnClickListener({
+            start<EitherActivity>()
+        })
+    }
+
+    private inline fun <reified T> start() {
+        startActivity(Intent(this, T::class.java))
     }
 }
diff --git a/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/either/EitherActivity.kt b/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/either/EitherActivity.kt
new file mode 100644
index 0000000..cfe2294
--- /dev/null
+++ b/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/either/EitherActivity.kt
@@ -0,0 +1,41 @@
+package com.danielecampogiani.androidfunctionalvalidation.either
+
+import android.arch.lifecycle.Observer
+import android.arch.lifecycle.ViewModelProviders
+import android.os.Bundle
+import android.support.v7.app.AppCompatActivity
+import android.widget.Toast
+import com.danielecampogiani.androidfunctionalvalidation.Data
+import com.danielecampogiani.androidfunctionalvalidation.R
+import kotlinx.android.synthetic.main.activity_input.*
+
+class EitherActivity : AppCompatActivity() {
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_input)
+
+        val viewModel = ViewModelProviders.of(this)[EitherViewModel::class.java]
+
+        signup_button.setOnClickListener {
+            viewModel.validate(email.text.toString(), number.text.toString())
+        }
+
+        viewModel.validation.observe(this, Observer {
+            it?.fold(this::handleLeft, this::handleRight)
+        })
+    }
+
+    private fun handleLeft(error: String) {
+        showMessage(error)
+    }
+
+    private fun handleRight(data: Data) {
+        val message = "Mail: ${data.mail} Phone: ${data.phone}"
+        showMessage(message)
+    }
+
+    private fun showMessage(message: String) {
+        Toast.makeText(this, message, Toast.LENGTH_SHORT).show()
+    }
+}
\ No newline at end of file
diff --git a/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/either/EitherViewModel.kt b/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/either/EitherViewModel.kt
new file mode 100644
index 0000000..e8284ac
--- /dev/null
+++ b/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/either/EitherViewModel.kt
@@ -0,0 +1,21 @@
+package com.danielecampogiani.androidfunctionalvalidation.either
+
+import android.arch.lifecycle.LiveData
+import android.arch.lifecycle.MutableLiveData
+import android.arch.lifecycle.ViewModel
+import com.danielecampogiani.androidfunctionalvalidation.Data
+import kategory.Either
+
+class EitherViewModel : ViewModel() {
+
+    private val mutableValidation: MutableLiveData<Either<String, Data>> = MutableLiveData()
+
+    val validation: LiveData<Either<String, Data>>
+        get() = mutableValidation
+
+
+    fun validate(mail: String, phoneNumber: String) {
+        mutableValidation.value = validateData(mail, phoneNumber)
+    }
+
+}
\ No newline at end of file
diff --git a/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/either/functions.kt b/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/either/functions.kt
new file mode 100644
index 0000000..e4834e9
--- /dev/null
+++ b/app/src/main/java/com/danielecampogiani/androidfunctionalvalidation/either/functions.kt
@@ -0,0 +1,26 @@
+package com.danielecampogiani.androidfunctionalvalidation.either
+
+import com.danielecampogiani.androidfunctionalvalidation.Data
+import com.danielecampogiani.androidfunctionalvalidation.validMail
+import com.danielecampogiani.androidfunctionalvalidation.validNumber
+import kategory.*
+
+fun validateData(mail: String, phoneNumber: String): Either<String, Data> {
+
+    return Either.applicative<String>().map2(mail.optionMail(), phoneNumber.optionPhoneNumber()) {
+        Data(it.a, it.b)
+    }.ev()
+
+}
+
+private fun String.optionMail(): Either<String, String> =
+        when {
+            validMail(this) -> this.right()
+            else -> "Invalid email".left()
+        }
+
+private fun String.optionPhoneNumber(): Either<String, String> =
+        when {
+            validNumber(this) -> this.right()
+            else -> "Invalid phone number".left()
+        }
\ No newline at end of file
diff --git a/app/src/main/res/layout/activity_main.xml b/app/src/main/res/layout/activity_main.xml
index 2917e10..a1bbbb4 100644
--- a/app/src/main/res/layout/activity_main.xml
+++ b/app/src/main/res/layout/activity_main.xml
@@ -18,4 +18,16 @@
         app:layout_constraintRight_toRightOf="parent"
         app:layout_constraintTop_toTopOf="parent" />
 
+    <android.support.v7.widget.AppCompatButton
+        android:id="@+id/either_button"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:backgroundTint="@color/primary"
+        android:text="@string/either"
+        android:textColor="@color/icons"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintLeft_toLeftOf="parent"
+        app:layout_constraintRight_toRightOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/option_button" />
+
 </android.support.constraint.ConstraintLayout>
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 35ef0bb..55301fb 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -5,4 +5,5 @@
     <string name="sign_up">Sign Up</string>
     <string name="option" translatable="false">Option</string>
     <string name="option_wrong">At least one field is wrong</string>
+    <string name="either" translatable="false">Either</string>
 </resources>