combination of traversals

src/combinations.rs

@@ -1,8 +1,13 @@
-use crate::lenses::{Lens, LensOver, LensView};
+use crate::{
+    lenses::{Lens, LensOver, LensView},
+    traversals::{Traversal, TraversalOver, TraversalTraverse},
+};
 
 #[derive(Clone, Copy)]
 pub struct Combination<A, B>(A, B);
 
+// additions
+
 impl<A, B> std::ops::Add<Lens<B>> for Lens<A> {
     type Output = Lens<Combination<Lens<A>, Lens<B>>>;
 
@@ -10,6 +15,29 @@ impl<A, B> std::ops::Add<Lens<B>> for Lens<A> {
         Lens(Combination(self, rhs))
     }
 }
+impl<A, B> std::ops::Add<Traversal<B>> for Traversal<A> {
+    type Output = Traversal<Combination<Traversal<A>, Traversal<B>>>;
+
+    fn add(self, rhs: Traversal<B>) -> Self::Output {
+        Traversal(Combination(self, rhs))
+    }
+}
+impl<A, B> std::ops::Add<Lens<B>> for Traversal<A> {
+    type Output = Traversal<Combination<Traversal<A>, Traversal<Lens<B>>>>;
+
+    fn add(self, rhs: Lens<B>) -> Self::Output {
+        Traversal(Combination(self, rhs.to_traversal()))
+    }
+}
+impl<A, B> std::ops::Add<Traversal<B>> for Lens<A> {
+    type Output = Traversal<Combination<Traversal<Lens<A>>, Traversal<B>>>;
+
+    fn add(self, rhs: Traversal<B>) -> Self::Output {
+        Traversal(Combination(self.to_traversal(), rhs))
+    }
+}
+
+// trait impls for Combination
 
 impl<A, B, T> LensView<T> for Combination<A, B>
 where
@@ -35,3 +63,32 @@ where
         A::over(&self.0, thing, |b| B::over(&self.1, b, f))
     }
 }
+
+impl<A, B, T> TraversalTraverse<T> for Combination<A, B>
+where
+    A: TraversalTraverse<T>,
+    B: TraversalTraverse<A::Field>,
+{
+    type Field = B::Field;
+
+    fn traverse(&self, thing: T) -> Vec<Self::Field> {
+        let a = A::traverse(&self.0, thing);
+        a.into_iter()
+            .map(|v| B::traverse(&self.1, v))
+            .flatten()
+            .collect()
+    }
+}
+
+impl<A, B, T> TraversalOver<T> for Combination<A, B>
+where
+    A: TraversalOver<T>,
+    B: TraversalOver<A::Field>,
+{
+    fn over<F>(&self, thing: T, mut f: F) -> T
+    where
+        F: FnMut(Self::Field) -> Self::Field,
+    {
+        A::over(&self.0, thing, |b| B::over(&self.1, b, &mut f))
+    }
+}

src/lenses/lens.rs

@@ -3,16 +3,16 @@ use crate::lenses::{Lens, LensOver, LensView};
 type Getter<T, U> = dyn Fn(T) -> U;
 type Setter<T, U> = dyn Fn(T, U) -> T;
 
-pub struct LensInner<T, U>(pub(crate) Box<Getter<T, U>>, pub(crate) Box<Setter<T, U>>);
+pub struct FuncLens<T, U>(pub(crate) Box<Getter<T, U>>, pub(crate) Box<Setter<T, U>>);
 
-impl<T, U> LensView<T> for LensInner<T, U> {
+impl<T, U> LensView<T> for FuncLens<T, U> {
     type Field = U;
 
     fn view(&self, thing: T) -> Self::Field {
         (self.0)(thing)
     }
 }
-impl<T: Clone, U> LensOver<T> for LensInner<T, U> {
+impl<T: Clone, U> LensOver<T> for FuncLens<T, U> {
     fn over<F>(&self, thing: T, f: F) -> T
     where
         F: FnOnce(Self::Field) -> Self::Field,
@@ -30,13 +30,13 @@ impl<T: Clone, U> LensOver<T> for LensInner<T, U> {
 pub fn lens_from_boxed<T, U>(
     getter: Box<Getter<T, U>>,
     setter: Box<Setter<T, U>>,
-) -> Lens<LensInner<T, U>> {
-    Lens(LensInner(getter, setter))
+) -> Lens<FuncLens<T, U>> {
+    Lens(FuncLens(getter, setter))
 }
 /// Makes a lens that implements `LensView<T>` and `LensOver<T>` with the provided functions
 pub fn lens<T, U>(
     getter: impl Fn(T) -> U + 'static,
     setter: impl Fn(T, U) -> T + 'static,
-) -> Lens<LensInner<T, U>> {
-    Lens(LensInner(Box::new(getter), Box::new(setter)))
+) -> Lens<FuncLens<T, U>> {
+    Lens(FuncLens(Box::new(getter), Box::new(setter)))
 }

src/lenses/mod.rs

@@ -11,28 +11,11 @@ pub use to::{to, to_from_boxed};
 mod lens;
 pub use lens::{lens, lens_from_boxed};
 
-use crate::traversals::Traversal;
-
 /// Wrapper type
 #[derive(Clone, Copy)]
 #[repr(transparent)]
 pub struct Lens<L>(pub(crate) L);
 
-// all lenses are traversals, so we can freely transform them into a traversal
-impl<L> Lens<L> {
-    /// Returns this lens as a traversal
-    pub fn to_traversal(self) -> Traversal<Lens<L>> {
-        Traversal(self)
-    }
-}
-// we can go back to a lens from a "traversal-ed" lens
-impl<L> Traversal<Lens<L>> {
-    /// Returns the wrapped lens
-    pub fn to_lens(self) -> Lens<L> {
-        self.0
-    }
-}
-
 /// For lenses that allow viewing
 pub trait LensView<T> {
     type Field;

src/lenses/to.rs

@@ -1,6 +1,6 @@
 use crate::lenses::{Lens, LensView};
 
-use super::lens::LensInner;
+use super::lens::FuncLens;
 
 pub struct ToInner<T, U>(Box<dyn Fn(T) -> U>);
 
@@ -23,7 +23,7 @@ pub fn to<T, U>(f: impl Fn(T) -> U + 'static) -> Lens<ToInner<T, U>> {
 
 impl<T, U> Lens<ToInner<T, U>> {
     /// Makes a full lens that implements `LensView<T>` and `LensOver<T>` with the provided functions
-    pub fn make_lens(self, setter: impl Fn(T, U) -> T + 'static) -> Lens<LensInner<T, U>> {
-        Lens(LensInner((self.0).0, Box::new(setter)))
+    pub fn make_lens(self, setter: impl Fn(T, U) -> T + 'static) -> Lens<FuncLens<T, U>> {
+        Lens(FuncLens((self.0).0, Box::new(setter)))
     }
 }

src/traversals/mod.rs

@@ -4,6 +4,8 @@ pub use both::both;
 mod each;
 pub use each::each;
 
+use crate::lenses::{Lens, LensOver, LensView};
+
 /// Wrapper type
 #[derive(Clone, Copy)]
 #[repr(transparent)]
@@ -14,7 +16,6 @@ pub trait TraversalTraverse<T> {
 
     fn traverse(&self, thing: T) -> Vec<Self::Field>;
 }
-
 pub trait TraversalOver<T>: TraversalTraverse<T> {
     fn over<F>(&self, thing: T, f: F) -> T
     where
@@ -27,6 +28,7 @@ pub trait TraversalOver<T>: TraversalTraverse<T> {
         Self::over(self, thing, move |_| v.clone())
     }
 }
+
 impl<L, T> TraversalTraverse<T> for Traversal<L>
 where
     L: TraversalTraverse<T>,
@@ -49,6 +51,42 @@ where
     }
 }
 
+// all lenses are traversals, so we can freely transform them into a traversal
+impl<L> Lens<L> {
+    /// Returns this lens as a traversal
+    pub fn to_traversal(self) -> Traversal<Lens<L>> {
+        Traversal(self)
+    }
+}
+// we can go back to a lens from a "traversal-ed" lens
+impl<L> Traversal<Lens<L>> {
+    /// Returns the wrapped lens
+    pub fn to_lens(self) -> Lens<L> {
+        self.0
+    }
+}
+impl<L, T> TraversalTraverse<T> for Lens<L>
+where
+    L: LensView<T>,
+{
+    type Field = L::Field;
+
+    fn traverse(&self, thing: T) -> Vec<Self::Field> {
+        vec![L::view(&self.0, thing)]
+    }
+}
+impl<L, T> TraversalOver<T> for Lens<L>
+where
+    L: LensView<T> + LensOver<T>,
+{
+    fn over<F>(&self, thing: T, f: F) -> T
+    where
+        F: FnMut(Self::Field) -> Self::Field,
+    {
+        L::over(&self.0, thing, f)
+    }
+}
+
 pub fn traverse<T, L: TraversalTraverse<T>>(lens: L, thing: T) -> Vec<L::Field> {
     L::traverse(&lens, thing)
 }
@@ -64,13 +102,59 @@ pub fn over<T, L: TraversalOver<T>>(lens: L, thing: T, f: impl FnMut(L::Field) -
 
 #[cfg(test)]
 mod tests {
+    use crate::lenses::_0;
+
     use super::*;
 
     #[test]
     fn traverse_each_works_on_arrays() {
         let array = [1, 2, 3, 4];
 
+        let res = each(array);
+        assert_eq!(res, vec![1, 2, 3, 4,]);
+
         let res = each(array, |v| v + 1);
         assert_eq!(res, [2, 3, 4, 5]);
     }
+
+    #[test]
+    fn can_combine_traversals() {
+        let array = [vec![1, 2], vec![3, 4]];
+
+        // combine two traversals
+        let res = (each + each)(array, |v| v + 1);
+        assert_eq!(res, [vec![2, 3], vec![4, 5]]);
+    }
+
+    #[test]
+    fn can_combine_traversal_with_lens() {
+        let array = [(1, 2), (3, 4), (5, 6)];
+
+        // combine a traversal with a lens
+        let t = each + _0;
+
+        // traverse
+        let res = t(array);
+        assert_eq!(res, vec![1, 3, 5]);
+
+        // over
+        let res = t(array, |v| v + 1);
+        assert_eq!(res, [(2, 2), (4, 4), (6, 6)]);
+    }
+
+    #[test]
+    fn can_combine_lens_with_traversal() {
+        let array = [(1, 2), (3, 4), (5, 6)];
+
+        // combine a traversal with a lens
+        let t = _0 + each;
+
+        // traverse
+        let res = t(array);
+        assert_eq!(res, vec![1, 2]);
+
+        // over
+        let res = t(array, |v| v + 1);
+        assert_eq!(res, [(2, 3), (3, 4), (5, 6)]);
+    }
 }