1 files changed, 73 insertions, 1 deletions
diff --git a/luatexbase-mcb.dtx b/luatexbase-mcb.dtx
index d9fb995..df95170 100644
--- a/luatexbase-mcb.dtx
+++ b/luatexbase-mcb.dtx
@@ -862,7 +862,7 @@ luatexbase.create_callback = create_callback
 %    \end{macrocode}
 %
 %    This function calls a callback. It can only call a callback created by
-%    the \texttt{create} function.
+%    the |create_callback| function.
 %
 %    \begin{macrocode}
 function call_callback(name, ...)
@@ -890,6 +890,74 @@ end
 luatexbase.call_callback = call_callback
 %    \end{macrocode}
 %
+%    |is_active_callback| checks the activation state of a given
+%    callback function. It is passed the description of the function
+%    and the name of the callback it was registered under.
+%
+%    The function raises an error if passed an invalid callback name
+%    or if the name or the description is missing.
+%    The return value is |true| iff the callback function is
+%    registered, |false| otherwise.
+%
+%    \begin{macrocode}
+--- string -> string -> bool
+luatexbase.is_active_callback = function (name, description)
+    if not name then
+        err ("unable to check for callback:\nno proper name passed")
+        return false
+    elseif not callbacktypes [name] then
+        err ("unable to check for callback %q:\nis not a valid callback", name)
+        return false
+    elseif not description then
+        err ("unable to check for callback %q:\nno description given", name)
+        return false
+    end
+    local lst = callbacklist [name]
+    if not lst then --- callback inactive, no functions registered
+        return false
+    end
+    for _, v in next, lst do
+        if v.description == description then --- success
+            return true
+        end
+    end
+    return false
+end
+%    \end{macrocode}
+%
+%    |callback_descriptions| returns a table containing all
+%    descriptions of the functions registered for a given callback in
+%    the order of their priority.
+%
+%    The function raises an error if the callback name is missing or
+%    invalid.
+%    If there is no function registered for the callback, an empty
+%    table is returned.
+%
+%    \begin{macrocode}
+--- string -> string list option
+luatexbase.callback_descriptions = function (name)
+    if not name then
+        err ("unable to check for callback:\nno proper name passed")
+        return
+    elseif not callbacktypes [name] then
+        err ("unable to check for callback %q:\nis not a valid callback", name)
+        return
+    end
+    local lst        = callbacklist [name]
+    local registered = { }
+    if lst then
+        for i = 1, #lst do
+            local itm = lst [i]
+            if i then
+                registered [i] = itm.description
+            end
+        end
+    end
+    return registered
+end
+%    \end{macrocode}
+%
 %    That's all folks!
 %
 %    \begin{macrocode}
@@ -913,13 +981,17 @@ local function sample(head,...)
     return head, true
 end
 local prio = luatexbase.priority_in_callback
+local is_active = luatexbase.is_active_callback
 msg("\n*********\n* Testing management functions\n*********")
 luatexbase.add_to_callback("hpack_filter", sample, "sample one", 1)
 luatexbase.add_to_callback("hpack_filter", sample, "sample two", 2)
 luatexbase.add_to_callback("hpack_filter", sample, "sample three", 1)
 assert(prio("hpack_filter", "sample three"))
+assert(is_active("hpack_filter", "sample three") == true)
+assert(#luatexbase.callback_descriptions("hpack_filter") == 3)
 luatexbase.remove_from_callback("hpack_filter", "sample three")
 assert(not prio("hpack_filter", "sample three"))
+assert(is_active("hpack_filter", "sample three") == false)
 luatexbase.reset_callback("hpack_filter")
 assert(not prio("hpack_filter", "sample one"))
 %    \end{macrocode}