From: Jim Pryor <profjim@jimpryor.net>
Date: Mon, 13 Dec 2010 06:42:40 +0000 (-0500)
Subject: transformers tweak
X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=8cd7f357e9a9d71795ec62eab0adb720f67d9011;ds=sidebyside

transformers tweak

Signed-off-by: Jim Pryor <profjim@jimpryor.net>
---

diff --git a/monad_transformers.mdwn b/monad_transformers.mdwn
index d3870978..f6de5308 100644
--- a/monad_transformers.mdwn
+++ b/monad_transformers.mdwn
@@ -450,7 +450,7 @@ TreeCont.monadize Continuation_monad.unit t1 initial_continuation;;
 	   (T.Node (T.Leaf 2, T.Leaf 3),
 		T.Node (T.Leaf 5, T.Node (T.Leaf 7, T.Leaf 11))))
 
-We can square each leaf. The meaning of `shift` will be explained in [[CPS and Continuation Operators]].
+We can square each leaf:
 <!--
 let initial_continuation = fun t -> t in
 TreeCont.monadize (fun a k -> k (a*a)) t1 initial_continuation;;
@@ -463,7 +463,13 @@ TreeCont.monadize (fun a k -> k (a*a)) t1 initial_continuation;;
 	   (T.Node (T.Leaf 4, T.Leaf 9),
 		T.Node (T.Leaf 25, T.Node (T.Leaf 49, T.Leaf 121))))
 
-We can count the leaves:
+The meaning of `shift` will be explained in [[CPS and Continuation Operators]]. Here you should just regard it as a primitive operation in our Continuation monad. In [this code](/code/tree_monadize.ml) you could simply write:
+
+	TreeCont.monadize (fun a -> fun k -> k (a*a)) t1 (fun t -> t);;
+
+But because of the way our monad library hides the underlying machinery, you can't just say `fun k -> k (a*a)`, you have to say `shift (fun k -> k (a*a))`.
+
+Moving on, we can count the leaves:
 <!--
 let initial_continuation = fun t -> 0 in
 TreeCont.monadize (fun a k -> 1 + k a) t1 initial_continuation;;
@@ -473,7 +479,7 @@ TreeCont.monadize (fun a k -> 1 + k a) t1 initial_continuation;;
 	- : int = 5
 
 
-We can convert the tree to a list of leaves:
+And we can convert the tree to a list of leaves:
 <!--
 let initial_continuation = fun t -> [] in
 TreeCont.monadize (fun a k -> a :: k a) t1 initial_continuation;;