--- a/mercurial/revset.py	Fri Mar 02 21:43:55 2012 +0200
+++ b/mercurial/revset.py	Fri Feb 24 11:02:21 2012 +0100
@@ -1319,5 +1319,20 @@
 
     return ret
 
+def prettyformat(tree):
+    def _prettyformat(tree, level, lines):
+        if not isinstance(tree, tuple) or tree[0] in ('string', 'symbol'):
+            lines.append((level, str(tree)))
+        else:
+            lines.append((level, '(%s' % tree[0]))
+            for s in tree[1:]:
+                _prettyformat(s, level + 1, lines)
+            lines[-1:] = [(lines[-1][0], lines[-1][1] + ')')]
+
+    lines = []
+    _prettyformat(tree, 0, lines)
+    output = '\n'.join(('  '*l + s) for l, s in lines)
+    return output
+
 # tell hggettext to extract docstrings from these functions:
 i18nfunctions = symbols.values()