diff -r 000000000000 -r c8e21d7dd685 src/pyams_utils/tales.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/pyams_utils/tales.py	Wed Dec 05 12:45:56 2018 +0100
@@ -0,0 +1,116 @@
+#
+# Copyright (c) 2008-2015 Thierry Florac <tflorac AT ulthar.net>
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE.
+#
+
+__docformat__ = 'restructuredtext'
+
+
+# import standard library
+import re
+
+# import interfaces
+from pyams_utils.interfaces.tales import ITALESExtension
+
+# import packages
+from chameleon.astutil import Symbol
+from chameleon.codegen import template
+from chameleon.tales import StringExpr
+from zope.contentprovider.tales import addTALNamespaceData
+
+
+class ContextExprMixin(object):
+    """Mixin-class for expression compilers"""
+
+    transform = None
+
+    def __call__(self, target, engine):
+        # Make call to superclass to assign value to target
+        assignment = super(ContextExprMixin, self).__call__(target, engine)
+        transform = template("target = transform(econtext, target)",
+                             target=target,
+                             transform=self.transform)
+        return assignment + transform
+
+
+FUNCTION_EXPRESSION = re.compile('(.+)\((.+)\)', re.MULTILINE | re.DOTALL)
+ARGUMENTS_EXPRESSION = re.compile('[^(,)]+')
+
+
+def render_extension(econtext, name):
+    """TALES extension renderer
+
+    See :ref:`tales` for complete description.
+    """
+
+    def get_value(econtext, arg):
+        """Extract argument value from context
+
+        Extension expression language is quite simple. Values can be given as
+        positioned strings, integers or named arguments of the same types.
+        """
+        arg = arg.strip()
+        if arg.startswith('"') or arg.startswith("'"):
+            # may be a quoted string...
+            return arg[1:-1]
+        if '=' in arg:
+            key, value = arg.split('=', 1)
+            value = get_value(econtext, value)
+            return {key.strip(): value}
+        try:
+            arg = int(arg)  # check integer value
+        except ValueError:
+            args = arg.split('.')
+            result = econtext.get(args.pop(0))
+            for arg in args:
+                result = getattr(result, arg)
+            return result
+        else:
+            return arg
+
+    name = name.strip()
+    context = econtext.get('context')
+    request = econtext.get('request')
+    view = econtext.get('view')
+
+    args, kwargs = [], {}
+    func_match = FUNCTION_EXPRESSION.match(name)
+    if func_match:
+        name, arguments = func_match.groups()
+        for arg in map(lambda x: get_value(econtext, x), ARGUMENTS_EXPRESSION.findall(arguments)):
+            if isinstance(arg, dict):
+                kwargs.update(arg)
+            else:
+                args.append(arg)
+
+    registry = request.registry
+    extension = registry.queryMultiAdapter((context, request, view), ITALESExtension, name=name)
+    if extension is None:
+        extension = registry.queryMultiAdapter((context, request), ITALESExtension, name=name)
+    if extension is None:
+        extension = registry.queryAdapter(context, ITALESExtension, name=name)
+
+    # provide a useful error message, if the extension was not found.
+    if extension is None:
+        return None
+
+    # Insert the data gotten from the context
+    addTALNamespaceData(extension, econtext)
+
+    return extension.render(*args, **kwargs)
+
+
+class ExtensionExpr(ContextExprMixin, StringExpr):
+    """tales: TALES expression
+
+    This expression can be used to call a custom named adapter providing ITALESExtension interface.
+    """
+
+    transform = Symbol(render_extension)