From ce48a0fbea5673d1eec5d758341c20f8e66887c0 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Date: Sun, 9 Jan 2011 17:07:53 -0500
Subject: [PATCH] Add sexp_cmp

---
 server/sexp.c | 19 +++++++++++++++++++
 server/sexp.h |  1 +
 2 files changed, 20 insertions(+)

diff --git a/server/sexp.c b/server/sexp.c
index 9e62490..9da78a4 100644
--- a/server/sexp.c
+++ b/server/sexp.c
@@ -155,6 +155,25 @@ cmsg_bytes_t sexp_data(sexp_t *x) {
   }
 }
 
+int sexp_cmp(sexp_t *a, sexp_t *b) {
+ tail:
+  if (a == b) return 0;
+  if (sexp_stringp(a) && sexp_stringp(b)) {
+    return cmsg_bytes_cmp(sexp_data(a), sexp_data(b));
+  }
+  if (sexp_pairp(a) && sexp_pairp(b)) {
+    int result = sexp_cmp(sexp_head(a), sexp_head(b));
+    if (result) return result;
+    a = sexp_tail(a);
+    b = sexp_tail(b);
+    goto tail;
+  }
+  if (a == NULL) return -1;
+  if (b == NULL) return 1;
+  if (a->kind < b->kind) return -1;
+  return 1;
+}
+
 sexp_t *sexp_assoc(sexp_t *list, cmsg_bytes_t key) {
   while (list != NULL) {
     sexp_t *candidate = sexp_head(list);
diff --git a/server/sexp.h b/server/sexp.h
index 1ed5f8d..2c9058f 100644
--- a/server/sexp.h
+++ b/server/sexp.h
@@ -65,6 +65,7 @@ static inline int sexp_pairp(sexp_t *x) {
 }
 
 extern cmsg_bytes_t sexp_data(sexp_t *x);
+extern int sexp_cmp(sexp_t *a, sexp_t *b);
 
 static inline sexp_t *sexp_head(sexp_t *x) {
   assert(x->kind == SEXP_PAIR);