join_can_be_expressed_via_bind

src/func/test_suite.rs

@@ -83,5 +83,10 @@ pub fn monad_follows_laws<'a, T: Monad<'a> + FunctorTestSuite<'a>>() -> R {
     T::sample(|pa| {
         res += fmap_can_be_expressed_via_bind::<T, _, _>(|x| x + 3, || pa(2));
     });
+    T::sample(|pa| {
+        T::sample(|pb| {
+            res += join_can_be_expressed_via_bind::<T, _>(|| pa(pb(2)));
+        })
+    });
     res
 }

src/func/tests.rs

@@ -347,3 +347,17 @@ pub fn tuple_can_be_expressed_via_la2<
         T::la2(fa0(), fb0(), |a, b| (a, b)),
     )
 }
+
+pub fn join_can_be_expressed_via_bind<
+    'a,
+    T: Monad<'a> + Eqr<'a>,
+    A: 'a + Send + Debug + PartialEq,
+>(
+    ffa0: impl Fn() -> T::F<T::F<A>>,
+) -> R {
+    T::eqr(
+        "join via bind: join x  =  x >>= id",
+        T::join(ffa0()),
+        T::bind(ffa0(), |fa| fa),
+    )
+}