lists-to-contin tweaks

[lambda.git] / from_lists_to_continuations.mdwn

diff --git a/from_lists_to_continuations.mdwn b/from_lists_to_continuations.mdwn
index c67d5e8..8c84dfb 100644 (file)
--- a/from_lists_to_continuations.mdwn
+++ b/from_lists_to_continuations.mdwn
@@ -19,9 +19,7 @@ updated version.
 
 Expected behavior:
 
-<pre>
-t "abSd" ~~> "ababd"
-</pre>   
+       t "abSd" ~~> "ababd"
 
 
 In linguistic terms, this is a kind of anaphora
@@ -32,39 +30,33 @@ This deceptively simple task gives rise to some mind-bending complexity.
 Note that it matters which 'S' you target first (the position of the *
 indicates the targeted 'S'):
 
-<pre>
-    t "aSbS" 
-        *
-~~> t "aabS" 
-          *
-~~> "aabaab"
-</pre>
+           t "aSbS" 
+               *
+       ~~> t "aabS" 
+                 *
+       ~~> "aabaab"
 
 versus
 
-<pre>
-    t "aSbS"
-          *
-~~> t "aSbaSb" 
-        *
-~~> t "aabaSb"
-           *
-~~> "aabaaabab"
-</pre>   
+           t "aSbS"
+                 *
+       ~~> t "aSbaSb" 
+               *
+       ~~> t "aabaSb"
+                  *
+       ~~> "aabaaabab"
 
 versus
 
-<pre>
-    t "aSbS"
-          *
-~~> t "aSbaSb"
-           *
-~~> t "aSbaaSbab"
-            *
-~~> t "aSbaaaSbaabab"
-             *
-~~> ...
-</pre>
+           t "aSbS"
+                 *
+       ~~> t "aSbaSb"
+                  *
+       ~~> t "aSbaaSbab"
+                   *
+       ~~> t "aSbaaaSbaabab"
+                    *
+       ~~> ...
 
 Aparently, this task, as simple as it is, is a form of computation,
 and the order in which the `'S'`s get evaluated can lead to divergent
@@ -80,20 +72,19 @@ zipper `unzipped` and `zipped`; we start with a fully zipped list, and
 move elements to the zipped part by pulling the zipper down until the
 entire list has been unzipped (and so the zipped half of the zipper is empty).
 
-<pre>
-type 'a list_zipper = ('a list) * ('a list);;
-
-let rec tz (z:char list_zipper) = 
-    match z with (unzipped, []) -> List.rev(unzipped) (* Done! *)
-               | (unzipped, 'S'::zipped) -> tz ((List.append unzipped unzipped), zipped) 
-               | (unzipped, target::zipped) -> tz (target::unzipped, zipped);; (* Pull zipper *)
-
-# tz ([], ['a'; 'b'; 'S'; 'd']);;
-- : char list = ['a'; 'b'; 'a'; 'b'; 'd']
-
-# tz ([], ['a'; 'S'; 'b'; 'S']);;
-- : char list = ['a'; 'a'; 'b'; 'a'; 'a'; 'b']
-</pre>
+       type 'a list_zipper = ('a list) * ('a list);;
+       
+       let rec tz (z:char list_zipper) = 
+           match z with
+           | (unzipped, []) -> List.rev(unzipped) (* Done! *)
+           | (unzipped, 'S'::zipped) -> tz ((List.append unzipped unzipped), zipped) 
+           | (unzipped, target::zipped) -> tz (target::unzipped, zipped);; (* Pull zipper *)
+       
+       # tz ([], ['a'; 'b'; 'S'; 'd']);;
+       - : char list = ['a'; 'b'; 'a'; 'b'; 'd']
+       
+       # tz ([], ['a'; 'S'; 'b'; 'S']);;
+       - : char list = ['a'; 'a'; 'b'; 'a'; 'a'; 'b']
 
 Note that this implementation enforces the evaluate-leftmost rule.
 Task completed.
@@ -162,23 +153,23 @@ The structure and the behavior will follow that of `tz` above, with
 some small but interesting differences.  We've included the orginal
 `tz` to facilitate detailed comparison:
 
-<pre>
-let rec tz (z:char list_zipper) = 
-    match z with (unzipped, []) -> List.rev(unzipped) (* Done! *)
-               | (unzipped, 'S'::zipped) -> tz ((List.append unzipped unzipped), zipped) 
-               | (unzipped, target::zipped) -> tz (target::unzipped, zipped);; (* Pull zipper *)
-
-let rec tc (l: char list) (c: (char list) -> (char list)) =
-  match l with [] -> List.rev (c [])
-             | 'S'::zipped -> tc zipped (fun x -> c (c x))
-             | target::zipped -> tc zipped (fun x -> target::(c x));;
-
-# tc ['a'; 'b'; 'S'; 'd'] (fun x -> x);;
-- : char list = ['a'; 'b'; 'a'; 'b']
-
-# tc ['a'; 'S'; 'b'; 'S'] (fun x -> x);;
-- : char list = ['a'; 'a'; 'b'; 'a'; 'a'; 'b']
-</pre>
+       let rec tz (z:char list_zipper) = 
+           match z with
+           | (unzipped, []) -> List.rev(unzipped) (* Done! *)
+           | (unzipped, 'S'::zipped) -> tz ((List.append unzipped unzipped), zipped) 
+           | (unzipped, target::zipped) -> tz (target::unzipped, zipped);; (* Pull zipper *)
+       
+       let rec tc (l: char list) (c: (char list) -> (char list)) =
+           match l with
+           | [] -> List.rev (c [])
+           | 'S'::zipped -> tc zipped (fun x -> c (c x))
+           | target::zipped -> tc zipped (fun x -> target::(c x));;
+       
+       # tc ['a'; 'b'; 'S'; 'd'] (fun x -> x);;
+       - : char list = ['a'; 'b'; 'a'; 'b']
+       
+       # tc ['a'; 'S'; 'b'; 'S'] (fun x -> x);;
+       - : char list = ['a'; 'a'; 'b'; 'a'; 'a'; 'b']
 
 To emphasize the parallel, I've re-used the names `zipped` and
 `target`.  The trace of the procedure will show that these variables