# HG changeset patch
# User Adam Chlipala <adamc@hcoop.net>
# Date 1236707205 14400
# Node ID ae374df5ccbdedb6850d5024debc12150e11ae91
# Parent  fb2a0e76dcef25db329d480b4ca7a179631f33cd
Prose for ListEdit

diff -r fb2a0e76dcef -r ae374df5ccbd demo/prose
--- a/demo/prose	Tue Mar 10 12:44:40 2009 -0400
+++ b/demo/prose	Tue Mar 10 13:46:45 2009 -0400
@@ -197,3 +197,11 @@
 <p>Most client-side JavaScript programs modify page contents imperatively, but Ur/Web is based on functional-reactive programming instead.  Programs allocate data sources and then describe the page as a pure function of those data sources.  When the sources change, the page changes automatically.</p>
 
 <p>Here's an example where a button modifies a data source that affects some text on the page.  The affected portion of the page is indicated with the pseudo-HTML tag <tt>dyn</tt>, whose <tt>signal</tt> attribute specifies one of these pure functions over mutable sources.  A source containing data of type <tt>t</tt> has type <tt>source t</tt> and is created with the <tt>source</tt> operation within the <tt>transaction</tt> monad.  Functions over sources are represented in the monad <tt>signal</tt>.  Like in Haskell, we overload monad notations, so that the same return and bind operators can be used to write signals and transactions.  The <tt>signal</tt> function coerces a source to a signal.</p>
+
+listEdit.urp
+
+<p>This is a more involved functional-reactive example, involving recursive data structures that contain sources.  We build a list editor similar to the one from the <tt>ListShop</tt> example, but with all editing happening on the client side.</p>
+
+<p>The central data structure is the <tt>rlist</tt>, a list whose individual elements are sources, enabling fine-grained mutation.  Every rlist is either nil or is a cons cell made up of a source for a string data element, another source to serve as a scratchpad for GUI-based edits to the data element, and a final source that stores the remainder of the list.</p>
+
+<p>The main program provides operations to append to a list and to edit the data stored at any cell of the list.  Append is implemented by maintaining a source <tt>head</tt>, which points to the first list element; and a source <tt>tailP</tt>, which points to a <tt>source rlist</tt> where we should place the next appended node.</p>
diff -r fb2a0e76dcef -r ae374df5ccbd src/elaborate.sml
--- a/src/elaborate.sml	Tue Mar 10 12:44:40 2009 -0400
+++ b/src/elaborate.sml	Tue Mar 10 13:46:45 2009 -0400
@@ -706,13 +706,6 @@
                                           ("#2", p_summary env {fields = fs2, unifs = #unifs s2, others = #others s2})]*)
 
          val (unifs1, unifs2) = eatMatching (fn ((_, r1), (_, r2)) => r1 = r2) (#unifs s1, #unifs s2)
-         fun eatMost unifs =
-             case unifs of
-                 (_, r) :: (rest as _ :: _) => (r := SOME (L'.CRecord (k, []), loc);
-                                                eatMost rest)
-               | _ => unifs
-         val unifs1 = eatMost unifs1
-         val unifs2 = eatMost unifs2
 
          val (others1, others2) = eatMatching (consEq env) (#others s1, #others s2)
          (*val () = eprefaces "Summaries3" [("#1", p_summary env {fields = fs1, unifs = unifs1, others = others1}),
@@ -887,6 +880,11 @@
              (L'.CError, _) => ()
            | (_, L'.CError) => ()
 
+           | (L'.CRecord _, _) => isRecord ()
+           | (_, L'.CRecord _) => isRecord ()
+           | (L'.CConcat _, _) => isRecord ()
+           | (_, L'.CConcat _) => isRecord ()
+
            | (L'.CUnif (_, k1, _, r1), L'.CUnif (_, k2, _, r2)) =>
              if r1 = r2 then
                  ()
@@ -1034,11 +1032,6 @@
            | (L'.TKFun (x, c1), L'.TKFun (_, c2)) =>
              unifyCons' (E.pushKRel env x) c1 c2
 
-           | (L'.CRecord _, _) => isRecord ()
-           | (_, L'.CRecord _) => isRecord ()
-           | (L'.CConcat _, _) => isRecord ()
-           | (_, L'.CConcat _) => isRecord ()
-
            | _ => err CIncompatible
      end