feat(deep_causality_haft): Added HKT Trait for Arity 5 together with Monad and MonadEffect for HKT5. Refactored code based. Added HKT type extension for Vec.

Signed-off-by: Marvin Hansen <[email protected]>

Author: marvin-hansen

deep_causality_haft/src/effect.rs

@@ -0,0 +1,61 @@
+/*
+ * SPDX-License-Identifier: MIT
+ * Copyright (c) "2025" . The DeepCausality Authors and Contributors. All Rights Reserved.
+ */
+
+// ----------------------------------------------------
+// Effect Traits (Arity 3)
+// ----------------------------------------------------
+
+use crate::{HKT, HKT3, HKT4, HKT5};
+
+/// Effect3: The Bridge Trait for Arity 3 Type Constructors.
+///
+/// This trait is implemented by a user-defined **System Witness** (e.g., `MyEffect`)
+/// to partially apply (fix) two of the three generic parameters of the HKT3 type.
+pub trait Effect3 {
+    /// The fixed type for the first parameter (e.g., the Error type E).
+    type Fixed1;
+
+    /// The fixed type for the second parameter (e.g., the Warning/Log type W).
+    type Fixed2;
+
+    /// The concrete witness type that implements HKT3 with the two fixed types.
+    /// It MUST implement HKT so we can pass it to Functor/Monad functions.
+    type HktWitness: HKT3<Self::Fixed1, Self::Fixed2> + HKT;
+}
+
+// ----------------------------------------------------
+// Effect Traits (Arity 4)
+// ----------------------------------------------------
+
+/// Effect4: The Bridge Trait for Arity 4 Type Constructors.I
+pub trait Effect4 {
+    /// The fixed type for the first parameter.
+    type Fixed1;
+
+    /// The fixed type for the second parameter.
+    type Fixed2;
+
+    /// The fixed type for the third parameter.
+    type Fixed3;
+
+    /// The concrete witness type that implements HKT4 with the three fixed types.
+    /// It MUST implement HKT so we can pass it to Functor/Monad functions.
+    type HktWitness: HKT4<Self::Fixed1, Self::Fixed2, Self::Fixed3> + HKT;
+}
+
+// ----------------------------------------------------
+// Effect Traits (Arity 5)
+// ----------------------------------------------------
+
+/// Effect5: The Bridge Trait for Arity 5 Type Constructors.
+pub trait Effect5 {
+    type Fixed1;
+    type Fixed2;
+    type Fixed3;
+    type Fixed4;
+
+    /// The concrete witness type that implements HKT5 with the four fixed types.
+    type HktWitness: HKT5<Self::Fixed1, Self::Fixed2, Self::Fixed3, Self::Fixed4> + HKT;
+}

deep_causality_haft/src/extensions.rs

@@ -0,0 +1,43 @@
+/*
+ * SPDX-License-Identifier: MIT
+ * Copyright (c) "2025" . The DeepCausality Authors and Contributors. All Rights Reserved.
+ */
+
+use crate::{Functor, HKT, Monad};
+
+// Witness for Option
+pub struct OptionWitness;
+
+impl HKT for OptionWitness {
+    type Type<T> = Option<T>;
+}
+
+// Implementation of Functor for OptionWitness
+impl Functor<OptionWitness> for OptionWitness {
+    fn fmap<A, B, Func>(
+        m_a: <OptionWitness as HKT>::Type<A>,
+        f: Func,
+    ) -> <OptionWitness as HKT>::Type<B>
+    where
+        Func: FnOnce(A) -> B,
+    {
+        m_a.map(f)
+    }
+}
+
+// Implementation of Monad for OptionWitness
+impl Monad<OptionWitness> for OptionWitness {
+    fn pure<T>(value: T) -> <OptionWitness as HKT>::Type<T> {
+        Some(value)
+    }
+
+    fn bind<A, B, Func>(
+        m_a: <OptionWitness as HKT>::Type<A>,
+        f: Func,
+    ) -> <OptionWitness as HKT>::Type<B>
+    where
+        Func: FnOnce(A) -> <OptionWitness as HKT>::Type<B>,
+    {
+        m_a.and_then(f)
+    }
+}

deep_causality_haft/src/extensions/hkt_option_ext.rs

@@ -0,0 +1,52 @@
+/*
+ * SPDX-License-Identifier: MIT
+ * Copyright (c) "2025" . The DeepCausality Authors and Contributors. All Rights Reserved.
+ */
+use crate::{Functor, HKT, HKT2, Monad, Placeholder};
+
+// Witness for Result<T, E> where E is fixed
+pub struct ResultWitness<E>(Placeholder, E);
+
+impl<E> HKT2<E> for ResultWitness<E> {
+    type Type<T> = Result<T, E>;
+}
+
+impl<E> HKT for ResultWitness<E> {
+    type Type<T> = Result<T, E>;
+}
+
+// Implementation of Functor for ResultWitness
+impl<E> Functor<ResultWitness<E>> for ResultWitness<E>
+where
+    E: 'static,
+{
+    fn fmap<A, B, Func>(
+        m_a: <ResultWitness<E> as HKT2<E>>::Type<A>,
+        f: Func,
+    ) -> <ResultWitness<E> as HKT2<E>>::Type<B>
+    where
+        Func: FnOnce(A) -> B,
+    {
+        m_a.map(f)
+    }
+}
+
+// Implementation of Monad for ResultWitness
+impl<E> Monad<ResultWitness<E>> for ResultWitness<E>
+where
+    E: 'static,
+{
+    fn pure<T>(value: T) -> <ResultWitness<E> as HKT2<E>>::Type<T> {
+        Ok(value)
+    }
+
+    fn bind<A, B, Func>(
+        m_a: <ResultWitness<E> as HKT2<E>>::Type<A>,
+        f: Func,
+    ) -> <ResultWitness<E> as HKT2<E>>::Type<B>
+    where
+        Func: FnOnce(A) -> <ResultWitness<E> as HKT2<E>>::Type<B>,
+    {
+        m_a.and_then(f)
+    }
+}

deep_causality_haft/src/extensions/hkt_result_ext.rs

@@ -0,0 +1,37 @@
+/*
+ * SPDX-License-Identifier: MIT
+ * Copyright (c) "2025" . The DeepCausality Authors and Contributors. All Rights Reserved.
+ */
+
+use crate::{Functor, HKT, Monad};
+
+// Witness for Vec<T>
+pub struct VecWitness;
+
+impl HKT for VecWitness {
+    type Type<T> = Vec<T>;
+}
+
+// Implementation of Functor for VecWitness
+impl Functor<VecWitness> for VecWitness {
+    fn fmap<A, B, Func>(m_a: <VecWitness as HKT>::Type<A>, f: Func) -> <VecWitness as HKT>::Type<B>
+    where
+        Func: FnMut(A) -> B,
+    {
+        m_a.into_iter().map(f).collect()
+    }
+}
+
+// Implementation of Monad for VecWitness
+impl Monad<VecWitness> for VecWitness {
+    fn pure<T>(value: T) -> <VecWitness as HKT>::Type<T> {
+        vec![value]
+    }
+
+    fn bind<A, B, Func>(m_a: <VecWitness as HKT>::Type<A>, f: Func) -> <VecWitness as HKT>::Type<B>
+    where
+        Func: FnMut(A) -> <VecWitness as HKT>::Type<B>,
+    {
+        m_a.into_iter().flat_map(f).collect()
+    }
+}

deep_causality_haft/src/extensions/hkt_vec_ext.rs

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+/*
+ * SPDX-License-Identifier: MIT
+ * Copyright (c) "2025" . The DeepCausality Authors and Contributors. All Rights Reserved.
+ */
+pub(crate) mod hkt_option_ext;
+pub(crate) mod hkt_result_ext;
+pub(crate) mod hkt_vec_ext;