moving on to the next revision and refinement. revisiting ideas.

docs/revision3.md

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+```
+given A
+def identity: A -> A
+    λ x => x
+end def
+
+given A
+class Semigroup A
+    def combine: A -> A -> A
+end class
+
+given A :: Semigroup
+class Monoid A
+    def empty: A
+end class
+
+given F *
+class Functor
+    given A
+    given B
+    def map: F A -> (A -> B) -> F B
+end class
+
+given F * :: Functor
+class Apply
+    given A
+    given B
+    def ap: F (A -> B) -> F A -> F B
+end class
+
+given F * :: Apply
+class Applicative
+    given A
+    def pure: A -> F A
+
+    def unit: F ()
+        pure ()
+    end def
+end class
+
+given F * :: Apply
+class FlatMap
+    given A
+    given B
+    def fmap: F A -> (A -> F B) -> F B
+
+    given A
+    def flatten: F (F A) -> F A
+        λ ffa => fmap ffa identity
+    end def
+end class
+
+given F * :: FlatMap, Applicative
+class Monad
+end class
+
+instance Semigroup Int32
+    def combine: Int32 -> Int32 -> Int32
+        int32_add
+    end def
+end instance
+
+given A :: Semigroup
+def +: A -> A -> A
+    combine
+end def
+
+def ex1: Int32 -> Int32
+    λ x => x + x
+end def
+
+def ex2: Int32 -> Int32
+    λ x => combine x x
+end def
+```