diff --git a/build.gradle b/build.gradle
index fceef9b6a..c8e04dda0 100644
--- a/build.gradle
+++ b/build.gradle
@@ -105,6 +105,12 @@ allprojects {
                 excludeGroup("Kotlin/Native")
             }
         }
+        maven {
+            url 'https://oss.jfrog.org/artifactory/oss-snapshot-local'
+            content {
+                excludeGroup("Kotlin/Native")
+            }
+        }
     }
     tasks.matching { it instanceof Test }.all {
         testLogging {
diff --git a/buildSrc/src/main/java/dependencies/Dep.kt b/buildSrc/src/main/java/dependencies/Dep.kt
index d121828f8..05d6903f7 100644
--- a/buildSrc/src/main/java/dependencies/Dep.kt
+++ b/buildSrc/src/main/java/dependencies/Dep.kt
@@ -91,6 +91,14 @@ object Dep {
         val serializationIos = "org.jetbrains.kotlinx:kotlinx-serialization-runtime-native:0.10.0"
     }
 
+    object Arrow {
+        val version = "0.9.0-SNAPSHOT"
+        val typeclasses = "io.arrow-kt:arrow-typeclasses:$version"
+        val data = "io.arrow-kt:arrow-effects-data:$version"
+        val extensions = "io.arrow-kt:arrow-effects-extensions:$version"
+        val ioExtensions = "io.arrow-kt:arrow-effects-io-extensions:$version"
+    }
+
     object Firebase {
         val core = "com.google.firebase:firebase-core:16.0.4"
         val fireStore = "com.google.firebase:firebase-firestore:17.1.3"
diff --git a/feature/session/build.gradle b/feature/session/build.gradle
index 65b230b53..cb7933e7e 100644
--- a/feature/session/build.gradle
+++ b/feature/session/build.gradle
@@ -27,6 +27,11 @@ dependencies {
     api Dep.Kotlin.coroutines
     implementation Dep.Kotlin.androidCoroutinesDispatcher
 
+    implementation Dep.Arrow.extensions
+    api Dep.Arrow.data
+    implementation Dep.Arrow.typeclasses
+    implementation Dep.Arrow.ioExtensions
+
     implementation Dep.AndroidX.appCompat
     implementation Dep.AndroidX.fragment
     implementation Dep.AndroidX.constraint
diff --git a/feature/session/src/main/java/io/github/droidkaigi/confsched2019/session/ui/SessionPagesFragment.kt b/feature/session/src/main/java/io/github/droidkaigi/confsched2019/session/ui/SessionPagesFragment.kt
index b95681513..5aa2d2b25 100644
--- a/feature/session/src/main/java/io/github/droidkaigi/confsched2019/session/ui/SessionPagesFragment.kt
+++ b/feature/session/src/main/java/io/github/droidkaigi/confsched2019/session/ui/SessionPagesFragment.kt
@@ -34,6 +34,8 @@ import io.github.droidkaigi.confsched2019.session.ui.widget.DaggerFragment
 import io.github.droidkaigi.confsched2019.user.store.UserStore
 import io.github.droidkaigi.confsched2019.util.ProgressTimeLatch
 import me.tatarka.injectedvmprovider.InjectedViewModelProviders
+import timber.log.Timber
+import timber.log.debug
 import javax.inject.Inject
 import javax.inject.Provider
 
@@ -87,6 +89,7 @@ class SessionPagesFragment : DaggerFragment() {
             sessionPagesActionCreator.load(sessionContentsStore.sessions)
         }
         sessionContentsStore.loadingState.changed(viewLifecycleOwner) { loadingState ->
+            Timber.debug { "Fragment:$loadingState" }
             progressTimeLatch.loading = loadingState.isLoading
         }
         sessionPagesStore.sessionScrollAdjusted.observe(viewLifecycleOwner) {
diff --git a/feature/session/src/main/java/io/github/droidkaigi/confsched2019/session/ui/actioncreator/SessionContentsActionCreator.kt b/feature/session/src/main/java/io/github/droidkaigi/confsched2019/session/ui/actioncreator/SessionContentsActionCreator.kt
index 57ed78745..6400b9eee 100644
--- a/feature/session/src/main/java/io/github/droidkaigi/confsched2019/session/ui/actioncreator/SessionContentsActionCreator.kt
+++ b/feature/session/src/main/java/io/github/droidkaigi/confsched2019/session/ui/actioncreator/SessionContentsActionCreator.kt
@@ -1,6 +1,15 @@
 package io.github.droidkaigi.confsched2019.session.ui.actioncreator
 
 import androidx.lifecycle.Lifecycle
+import arrow.Kind
+import arrow.core.Either
+import arrow.core.getOrHandle
+import arrow.core.left
+import arrow.effects.ForIO
+import arrow.effects.IO
+import arrow.effects.extensions.io.async.async
+import arrow.effects.extensions.io.fx.fx
+import arrow.effects.fix
 import io.github.droidkaigi.confsched2019.action.Action
 import io.github.droidkaigi.confsched2019.data.repository.SessionRepository
 import io.github.droidkaigi.confsched2019.di.PageScope
@@ -13,6 +22,7 @@ import io.github.droidkaigi.confsched2019.session.R
 import io.github.droidkaigi.confsched2019.system.actioncreator.ErrorHandler
 import io.github.droidkaigi.confsched2019.util.SessionAlarm
 import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.InternalCoroutinesApi
 import kotlinx.coroutines.launch
 import timber.log.Timber
 import timber.log.debug
@@ -66,27 +76,48 @@ class SessionContentsActionCreator @Inject constructor(
     }
 
     fun toggleFavorite(session: Session) {
-        launch {
-            try {
+        fx {
+            !effect {
                 dispatcher.dispatchLoadingState(LoadingState.LOADING)
                 sessionRepository.toggleFavorite(session)
                 sessionAlarm.toggleRegister(session)
                 val sessionContents = sessionRepository.sessionContents()
                 dispatcher.dispatch(Action.SessionContentsLoaded(sessionContents))
-                dispatcher.dispatchLoadingState(LoadingState.LOADED)
-            } catch (e: Exception) {
-                dispatcher.dispatch(
+                LoadingState.LOADED
+            }
+        }.runAndHold { result ->
+            val state = result.getOrHandle {
+                dispatcher.launchAndDispatch(
                     Action.ShowProcessingMessage(
                         Message.of(
                             R.string.session_favorite_connection_error
                         )
                     )
                 )
+                LoadingState.INITIALIZED
             }
+            dispatcher.launchAndDispatchLoadingState(state)
+        }
+    }
+
+    @UseExperimental(InternalCoroutinesApi::class)
+    private fun <A> Kind<ForIO, A>.runAndHold(result: (Either<Throwable, A>) -> Unit) {
+        IO.async().run {
+            defer(coroutineContext) {
+                this@runAndHold
+            }
+        }.fix().attempt().unsafeRunAsync {
+            result.invoke(it.getOrHandle { it.left() })
         }
     }
 
     private suspend fun Dispatcher.dispatchLoadingState(loadingState: LoadingState) {
+        println("Fragment: Dispatch $loadingState")
         dispatch(Action.SessionLoadingStateChanged(loadingState))
     }
+
+    private fun Dispatcher.launchAndDispatchLoadingState(loadingState: LoadingState) {
+        println("Fragment: Dispatch $loadingState")
+        launchAndDispatch(Action.SessionLoadingStateChanged(loadingState))
+    }
 }