From 4f2c619bb0971153c518f120c8911ce3a94f783d Mon Sep 17 00:00:00 2001
From: Adam Chlipala <adam@chlipala.net>
Date: Sun, 21 Nov 2010 15:43:24 -0500
Subject: Fix a bug in C list unurlification

---
 lib/ur/list.ur    | 14 ++++++++++++++
 lib/ur/list.urs   |  2 ++
 src/cjr_print.sml |  4 ++--
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/lib/ur/list.ur b/lib/ur/list.ur
index 71d8fa98..354ef132 100644
--- a/lib/ur/list.ur
+++ b/lib/ur/list.ur
@@ -308,6 +308,20 @@ fun sort [a] (gt : a -> a -> bool) (ls : t a) : t a =
         sort' ls
     end
 
+val nth [a] =
+    let
+        fun nth (ls : list a) (n : int) : option a =
+            case ls of
+                [] => None
+              | x :: ls' =>
+                if n <= 0 then
+                    Some x
+                else
+                    nth ls' (n-1)
+    in
+        nth
+    end
+
 fun assoc [a] [b] (_ : eq a) (x : a) =
     let
         fun assoc' (ls : list (a * b)) =
diff --git a/lib/ur/list.urs b/lib/ur/list.urs
index a0cec8fb..c23bf840 100644
--- a/lib/ur/list.urs
+++ b/lib/ur/list.urs
@@ -71,6 +71,8 @@ val mapQueryPartialM : tables ::: {{Type}} -> exps ::: {Type} -> t ::: Type
 
 val sort : a ::: Type -> (a -> a -> bool) (* > predicate *) -> t a -> t a
 
+val nth : a ::: Type -> list a -> int -> option a
+
 (** Association lists *)
 
 val assoc : a ::: Type -> b ::: Type -> eq a -> a -> t (a * b) -> option b
diff --git a/src/cjr_print.sml b/src/cjr_print.sml
index e440a53d..99b42657 100644
--- a/src/cjr_print.sml
+++ b/src/cjr_print.sml
@@ -861,7 +861,7 @@ fun unurlify fromClient env (t, loc) =
                                   space,
                                   string "+=",
                                   space,
-                                  string "3, NULL) : ((!strncmp(request, \"Cons\", 4) && (request[4] == 0 ",
+                                  string "3, (*request == '/' ? *request++ = 0 : 0), NULL) : ((!strncmp(request, \"Cons\", 4) && (request[4] == 0 ",
                                   string "|| request[4] == '/')) ? (request",
                                   space,
                                   string "+=",
@@ -895,7 +895,7 @@ fun unurlify fromClient env (t, loc) =
                                   newline,
                                   string ":",
                                   space,
-                                  string ("(uw_error(ctx, FATAL, \"Error unurlifying list\"), NULL))));"),
+                                  string ("(uw_error(ctx, FATAL, \"Error unurlifying list: %s\", request), NULL))));"),
                                   newline],
                              string "}",
                              newline,
-- 
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