Join for Reader

dialogues.md

@@ -1097,3 +1097,25 @@ to produce any part of their result).
 23:34 < Cale> So for instance, when you're repeatedly updating the contents of an IORef, or recursively updating an
 accumulating parameter without matching on it, you want to be careful there.
 ```
+
+## Join for Reader
+
+```
+18:51 < OscarZ> about join... im wondering about join (+) 7 = 14
+19:14 < pjdelport> OscarZ: join for Reader becomes even more Intuitive when you pronounce Reader e a as "function
+                   from an environment e to a"
+19:15 < pjdelport> Then "Reader e (Reader e a)" is just "function from an environment e to function from an
+                   environment e to a"
+19:16 < pjdelport> And joining means turning that into  just one "function from an environment e to a"
+19:16 < pjdelport> And saying it like that should (hopefully) make the implementation and what it does more obvious
+                   :)
+19:23 < pjdelport> I still think just pondering "type Reader e a = e -> a" is a great way to to get that "a ha"
+                   moment
+```
+
+```haskell
+λ> join (+) 7
+14
+λ> join (*) 7
+49
+```