From: Jim Pryor <profjim@jimpryor.net>
Date: Fri, 24 Dec 2010 03:38:42 +0000 (-0500)
Subject: ass10 hint tweaks
X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=f74ea8596e1ea2586dcf34fdcdb27b2bedf446a0

ass10 hint tweaks

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

diff --git a/hints/assignment_10_hint_3.mdwn b/hints/assignment_10_hint_3.mdwn
index 6a442a09..0523d67d 100644
--- a/hints/assignment_10_hint_3.mdwn
+++ b/hints/assignment_10_hint_3.mdwn
@@ -43,22 +43,26 @@ While we're at it, let's re-define our Reader monad too:
 
 Now instead of annotating leaves with the current store, we'll convert
 the leaves into "askers" that will wait for an environment and return what that
-environment says about the original leaf. At the same time, we'll update the store so that it knows how many leafs of each value have been seen:
+environment says about the original leaf. At the same time, we'll update the store so that it knows how many leafs of each value have been seen.
 
+We could proceed in two ways: we could either convert the leafs into "askers" now, and then use `TR.monadize` to conver the tree of askers into a tree-asker (that is, a function from an environment to a tree). Or we could just pass the leaves through unchanged for the moment, and leave the job of converting them to askers to the `TR.monadize` pass. We'll take the second strategy. (This turns out to fit better with what we go on to do later.) Hence, this first pass, using `TS.monadize`, only has to update the store.
 
-    let annotater : char -> ((char -> int) -> int) State_custom.m =
-        fun a s -> ((fun e -> e a), update_env s a);;
+
+    let annotater : char -> char State_custom.m =
+        fun a s -> (a, update_env s a);;
 
     let v2 = TS.monadize annotater tree (fun a -> 0);;
 
 
 The seed function here is an environment that by default maps every leaf
-element to 0. In the end, `v2` consists of a pair of a tree of askers, and a
-`char -> int` environment. We can use `TR.monadize` to convert that tree of
-askers into a tree-asker, that is, a function from an environment to a tree. And we then feed it the very environment that was `v2`'s final store:
+element to 0. In the end, `v2` consists of a pair of a tree and a
+`char -> int` environment. We can use `TR.monadize` to convert that tree into a tree-asker, that is, a function from an environment to a tree. And we then feed it the very environment that was `v2`'s final store:
+
+    let asker : char -> int Reader_custom.m =
+      fun (a : char) -> fun (env : char -> int) -> env a;;
 
-    let (tree',env) = v2
-    in TR.monadize (fun a -> a) tree' env;;
+    let (t, env) = v2
+    in TR.monadize asker t env;;
 
 
 This gives us a tree of `int`s, where each `int` replaces the original `char`