diff --git a/src/func.rs b/src/func.rs
index 1efdf45..0dfe28f 100644
--- a/src/func.rs
+++ b/src/func.rs
@@ -9,18 +9,20 @@
 
 pub mod classes;
 pub mod clone_func;
+mod controlflow;
 pub mod copy_func;
 pub mod derivations;
-mod istate;
 #[cfg(test)]
 pub mod test_suite;
 #[cfg(test)]
 pub mod tests;
 
-pub use self::istate::IState;
-use self::istate::IStateClass;
+pub use std::ops::ControlFlow;
+
 pub use radn_derive::{CovariantFunctor, SharedFunctor};
 
+pub use self::controlflow::ControlFlowClass;
+
 /// Part of Haskell's `Functor f` responsible to use `f a`.
 ///
 /// <https://hackage.haskell.org/package/base-4.18.0.0/docs/Data-Functor.html>
@@ -177,7 +179,7 @@ pub trait Monad: Applicative {
     /// On practice, you shouldn't be using [`Monad::bind`]/[`Pure::pure`]/[`Functor::fmap`] here.
     fn ibind<'a, A: 'a, B: 'a>(
         a: A,
-        f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a;
@@ -222,11 +224,13 @@ pub trait Alternative: Applicative {
 /// Represents wrapped results which are instantly available.
 pub trait LocalFunctor: WeakFunctor {
     /// Extract iteration state, if successful.
-    fn unstuff<'a, A: 'a, B: 'a>(state: Self::F<'a, IState<A, B>>) -> IState<A, Self::F<'a, B>>
+    fn unstuff<'a, A: 'a, B: 'a>(
+        state: Self::F<'a, ControlFlow<B, A>>,
+    ) -> ControlFlow<Self::F<'a, B>, A>
     where
         Self: 'a,
     {
-        Self::stuff::<_, IStateClass<A>>(state)
+        Self::stuff::<_, ControlFlowClass<A>>(state)
     }
 
     /// Stuff wrapped result into another functor.
diff --git a/src/func/classes/composition.rs b/src/func/classes/composition.rs
index c614de7..7261f69 100644
--- a/src/func/classes/composition.rs
+++ b/src/func/classes/composition.rs
@@ -101,7 +101,7 @@ impl<U: Monad, V: Monad + LocalFunctor> Monad for CompositionClass<U, V> {
 
     fn ibind<'a, A: 'a, B: 'a>(
         a: A,
-        mut f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        mut f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a,
@@ -132,7 +132,9 @@ impl<E, U: Monad, V: MonadFail<E> + LocalFunctor> MonadFail<E> for CompositionCl
 }
 
 impl<U: LocalFunctor + Functor, V: LocalFunctor> LocalFunctor for CompositionClass<U, V> {
-    fn unstuff<'a, A: 'a, B: 'a>(state: Self::F<'a, IState<A, B>>) -> IState<A, Self::F<'a, B>>
+    fn unstuff<'a, A: 'a, B: 'a>(
+        state: Self::F<'a, ControlFlow<B, A>>,
+    ) -> ControlFlow<Self::F<'a, B>, A>
     where
         Self: 'a,
     {
diff --git a/src/func/classes/future.rs b/src/func/classes/future.rs
index db00e22..dbf3e9f 100644
--- a/src/func/classes/future.rs
+++ b/src/func/classes/future.rs
@@ -89,7 +89,7 @@ impl Monad for FutureClass {
 
     fn ibind<'a, A: 'a, B: 'a>(
         mut a: A,
-        mut f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        mut f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a,
@@ -97,8 +97,8 @@ impl Monad for FutureClass {
         Box::pin(async move {
             loop {
                 match f(a).await {
-                    IState::Pending(next_a) => a = next_a,
-                    IState::Done(b) => return b,
+                    ControlFlow::Continue(next_a) => a = next_a,
+                    ControlFlow::Break(b) => return b,
                 };
             }
         })
diff --git a/src/func/classes/lazy.rs b/src/func/classes/lazy.rs
index 63169f6..8128dbf 100644
--- a/src/func/classes/lazy.rs
+++ b/src/func/classes/lazy.rs
@@ -90,15 +90,15 @@ impl Monad for LazyClass {
 
     fn ibind<'a, A: 'a, B: 'a>(
         mut a: A,
-        mut f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        mut f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a,
     {
         Box::new(move || loop {
             match f(a)() {
-                IState::Pending(next_a) => a = next_a,
-                IState::Done(b) => return b,
+                ControlFlow::Continue(next_a) => a = next_a,
+                ControlFlow::Break(b) => return b,
             };
         })
     }
diff --git a/src/func/classes/option.rs b/src/func/classes/option.rs
index 4d7f752..8106158 100644
--- a/src/func/classes/option.rs
+++ b/src/func/classes/option.rs
@@ -94,15 +94,15 @@ impl Monad for OptionClass {
 
     fn ibind<'a, A: 'a, B: 'a>(
         mut a: A,
-        mut f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        mut f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a,
     {
         loop {
             match f(a)? {
-                IState::Pending(next_a) => a = next_a,
-                IState::Done(b) => return Self::pure(b),
+                ControlFlow::Continue(next_a) => a = next_a,
+                ControlFlow::Break(b) => return Self::pure(b),
             };
         }
     }
@@ -113,14 +113,16 @@ impl Monad for OptionClass {
 }
 
 impl LocalFunctor for OptionClass {
-    fn unstuff<'a, A: 'a, B: 'a>(state: Self::F<'a, IState<A, B>>) -> IState<A, Self::F<'a, B>>
+    fn unstuff<'a, A: 'a, B: 'a>(
+        state: Self::F<'a, ControlFlow<B, A>>,
+    ) -> ControlFlow<Self::F<'a, B>, A>
     where
         Self: 'a,
     {
         match state {
-            Some(IState::Pending(a)) => IState::Pending(a),
-            Some(IState::Done(b)) => IState::Done(Some(b)),
-            None => IState::Done(None),
+            Some(ControlFlow::Continue(a)) => ControlFlow::Continue(a),
+            Some(ControlFlow::Break(b)) => ControlFlow::Break(Some(b)),
+            None => ControlFlow::Break(None),
         }
     }
 
diff --git a/src/func/classes/result.rs b/src/func/classes/result.rs
index 03d4424..0649a60 100644
--- a/src/func/classes/result.rs
+++ b/src/func/classes/result.rs
@@ -115,15 +115,15 @@ impl<E> Monad for ResultClass<E> {
 
     fn ibind<'a, A: 'a, B: 'a>(
         mut a: A,
-        mut f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        mut f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a,
     {
         loop {
             match f(a)? {
-                IState::Pending(next_a) => a = next_a,
-                IState::Done(b) => return Self::pure(b),
+                ControlFlow::Continue(next_a) => a = next_a,
+                ControlFlow::Break(b) => return Self::pure(b),
             };
         }
     }
@@ -137,14 +137,16 @@ impl<E> Monad for ResultClass<E> {
 }
 
 impl<E> LocalFunctor for ResultClass<E> {
-    fn unstuff<'a, A: 'a, B: 'a>(state: Self::F<'a, IState<A, B>>) -> IState<A, Self::F<'a, B>>
+    fn unstuff<'a, A: 'a, B: 'a>(
+        state: Self::F<'a, ControlFlow<B, A>>,
+    ) -> ControlFlow<Self::F<'a, B>, A>
     where
         Self: 'a,
     {
         match state {
-            Ok(IState::Pending(a)) => IState::Pending(a),
-            Ok(IState::Done(b)) => IState::Done(Ok(b)),
-            Err(e) => IState::Done(Err(e)),
+            Ok(ControlFlow::Continue(a)) => ControlFlow::Continue(a),
+            Ok(ControlFlow::Break(b)) => ControlFlow::Break(Ok(b)),
+            Err(e) => ControlFlow::Break(Err(e)),
         }
     }
 
diff --git a/src/func/classes/solo.rs b/src/func/classes/solo.rs
index 18d17f8..94b7650 100644
--- a/src/func/classes/solo.rs
+++ b/src/func/classes/solo.rs
@@ -82,15 +82,15 @@ impl Monad for SoloClass {
 
     fn ibind<'a, A: 'a, B: 'a>(
         mut a: A,
-        mut f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        mut f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a,
     {
         loop {
             match f(a) {
-                IState::Pending(next_a) => a = next_a,
-                IState::Done(b) => return b,
+                ControlFlow::Continue(next_a) => a = next_a,
+                ControlFlow::Break(b) => return b,
             };
         }
     }
@@ -101,7 +101,9 @@ impl Monad for SoloClass {
 }
 
 impl LocalFunctor for SoloClass {
-    fn unstuff<'a, A: 'a, B: 'a>(state: Self::F<'a, IState<A, B>>) -> IState<A, Self::F<'a, B>>
+    fn unstuff<'a, A: 'a, B: 'a>(
+        state: Self::F<'a, ControlFlow<B, A>>,
+    ) -> ControlFlow<Self::F<'a, B>, A>
     where
         Self: 'a,
     {
diff --git a/src/func/classes/stackless.rs b/src/func/classes/stackless.rs
index abbb162..e9b0bf3 100644
--- a/src/func/classes/stackless.rs
+++ b/src/func/classes/stackless.rs
@@ -226,15 +226,15 @@ impl Monad for StacklessClass {
 
     fn ibind<'a, A: 'a, B: 'a>(
         a: A,
-        mut f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        mut f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a,
     {
         Self::pure(a).bind(move |a| {
             f(a).bind(|state| match state {
-                IState::Pending(a) => Self::ibind(a, f),
-                IState::Done(b) => Self::pure(b),
+                ControlFlow::Continue(a) => Self::ibind(a, f),
+                ControlFlow::Break(b) => Self::pure(b),
             })
         })
     }
diff --git a/src/func/controlflow.rs b/src/func/controlflow.rs
new file mode 100644
index 0000000..9f59dbb
--- /dev/null
+++ b/src/func/controlflow.rs
@@ -0,0 +1,30 @@
+use super::*;
+
+pub struct ControlFlowClass<C>(ControlFlow<(), C>);
+
+impl<C> WeakFunctor for ControlFlowClass<C> {
+    type F<'a, A: 'a> =  ControlFlow<A, C>
+    where
+        Self: 'a;
+}
+
+impl<C> Functor for ControlFlowClass<C> {
+    fn fmap<'a, A: 'a, B: 'a>(f: impl 'a + FnOnce(A) -> B, fa: Self::F<'a, A>) -> Self::F<'a, B>
+    where
+        Self: 'a,
+    {
+        match fa {
+            ControlFlow::Continue(c) => ControlFlow::Continue(c),
+            ControlFlow::Break(a) => ControlFlow::Break(f(a)),
+        }
+    }
+}
+
+impl<C> Pure for ControlFlowClass<C> {
+    fn pure<'a, A: 'a>(a: A) -> Self::F<'a, A>
+    where
+        Self: 'a,
+    {
+        ControlFlow::Break(a)
+    }
+}
diff --git a/src/func/istate.rs b/src/func/istate.rs
deleted file mode 100644
index 2efd8e4..0000000
--- a/src/func/istate.rs
+++ /dev/null
@@ -1,44 +0,0 @@
-use super::*;
-
-/// Represents iteration state. Used in [`Monad::ibind`].
-///
-/// [`IState<P, D>`] is isomorphic to [`Result<D, P>`].
-pub enum IState<P, D> {
-    /// Loop running.
-    ///
-    /// Isomorphic to [`Result::Err`].
-    Pending(P),
-    /// Loop finished.
-    ///
-    /// Isomorphic to [`Result::Ok`].
-    Done(D),
-}
-
-pub struct IStateClass<P>(P);
-
-impl<P> WeakFunctor for IStateClass<P> {
-    type F<'a, A: 'a> = IState<P, A>
-    where
-        Self: 'a;
-}
-
-impl<P> Functor for IStateClass<P> {
-    fn fmap<'a, A: 'a, B: 'a>(f: impl 'a + FnOnce(A) -> B, fa: Self::F<'a, A>) -> Self::F<'a, B>
-    where
-        Self: 'a,
-    {
-        match fa {
-            IState::Pending(p) => IState::Pending(p),
-            IState::Done(d) => IState::Done(f(d)),
-        }
-    }
-}
-
-impl<P> Pure for IStateClass<P> {
-    fn pure<'a, A: 'a>(a: A) -> Self::F<'a, A>
-    where
-        Self: 'a,
-    {
-        IState::Done(a)
-    }
-}
diff --git a/src/std/collections/stack.rs b/src/std/collections/stack.rs
index 889a5c1..7062074 100644
--- a/src/std/collections/stack.rs
+++ b/src/std/collections/stack.rs
@@ -158,17 +158,17 @@ impl<'a, Ctx: 'a + Context, A: Mentionable<'a, Ctx>> ExtStack<'a, Ctx, A> for St
     }
     fn vec(self) -> StackVecWrapped<'a, Ctx, A> {
         Ctx::T::ibind((vec![], self), |(mut vec, stack)| match stack {
-            Nullable::Null(_) => Ctx::T::pure(IState::Done(Ok(vec))),
+            Nullable::Null(_) => Ctx::T::pure(ControlFlow::Break(Ok(vec))),
             Nullable::NotNull(point) => Ctx::T::fmap(
                 |resolved| {
                     let node = match resolved {
                         Ok(node) => node,
                         Err(error) => {
-                            return IState::Done(Err(error));
+                            return ControlFlow::Break(Err(error));
                         }
                     };
                     vec.push(node.element.clone());
-                    IState::Pending((vec, node.rest.clone()))
+                    ControlFlow::Continue((vec, node.rest.clone()))
                 },
                 point.resolve(),
             ),
diff --git a/src/std/tracing.rs b/src/std/tracing.rs
index f021cab..dcc9d00 100644
--- a/src/std/tracing.rs
+++ b/src/std/tracing.rs
@@ -165,7 +165,7 @@ impl Monad for TracedClass {
 
     fn ibind<'a, A: 'a, B: 'a>(
         mut a: A,
-        mut f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        mut f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a,
@@ -175,8 +175,8 @@ impl Monad for TracedClass {
             let fa = f(a);
             t = fa.t.after(t);
             match fa.a {
-                IState::Pending(next_a) => a = next_a,
-                IState::Done(b) => return b.with_trace(t),
+                ControlFlow::Continue(next_a) => a = next_a,
+                ControlFlow::Break(b) => return b.with_trace(t),
             }
         }
     }
diff --git a/src/testing/counted.rs b/src/testing/counted.rs
index 66379a3..edfb673 100644
--- a/src/testing/counted.rs
+++ b/src/testing/counted.rs
@@ -147,7 +147,7 @@ impl Monad for CountedClass {
 
     fn ibind<'a, A: 'a, B: 'a>(
         mut a: A,
-        mut f: impl 'a + FnMut(A) -> Self::F<'a, IState<A, B>>,
+        mut f: impl 'a + FnMut(A) -> Self::F<'a, ControlFlow<B, A>>,
     ) -> Self::F<'a, B>
     where
         Self: 'a,
@@ -157,8 +157,8 @@ impl Monad for CountedClass {
             let fa = f(a);
             n += fa.n;
             match fa.a {
-                IState::Pending(next_a) => a = next_a,
-                IState::Done(b) => return b.with_count(n),
+                ControlFlow::Continue(next_a) => a = next_a,
+                ControlFlow::Break(b) => return b.with_count(n),
             }
         }
     }