diff --git a/custom_functions_you_can_override.lua b/custom_functions_you_can_override.lua
index 35aadcd..b487ee0 100644
--- a/custom_functions_you_can_override.lua
+++ b/custom_functions_you_can_override.lua
@@ -294,7 +294,19 @@ yl_speak_up.custom_functions_a_[ "example function" ] = {
 			"label[0.5,8.0;It is up to the custom function to make whatever sense it wants "..
 				"\nout of these parameters.]"
 	end,
-	-- TODO: function for evaluating the input
+	-- this function will be called by the one that handles all custom input to actions
+	-- of the type "evaluate"; it can change the value of entries of the table "fields"
+	-- if necessary
+	code_input_handler = function(player, n_id, a, formname, fields)
+		local pname = player:get_player_name()
+		-- let's just tell the player the value of "fields" (after all this is an
+		-- example function)
+		minetest.chat_send_player(pname, "The custom action input handler \""..
+			minetest.formspec_escape(tostring(a.a_value)).."\" was called with "..
+			"the following input:\n"..minetest.serialize(fields))
+		-- the function has to return fields
+		return fields
+	end,
 }
 
 
diff --git a/exec_actions.lua b/exec_actions.lua
index 104bbec..ed025e6 100644
--- a/exec_actions.lua
+++ b/exec_actions.lua
@@ -696,14 +696,23 @@ end
 
 -- action of the type "evaluate"
 yl_speak_up.input_fs_action_evaluate = function(player, formname, fields)
-	-- TODO: handle custom functions
+	local pname = player:get_player_name()
+	local a_id = yl_speak_up.speak_to[pname].a_id
+	-- the custom input_handler may have something to say here as well
+	local a = yl_speak_up.get_action_by_player(player)
+	if(player and a and a.a_value) then
+		local custom_data = yl_speak_up.custom_functions_a_[a.a_value]
+		if(custom_data and custom_data.code_input_handler) then
+			local fun = custom_data.code_input_handler
+			-- actually call the function (which may change the value of fields)
+			fields = fun(player, n_id, a, formname, fields)
+		end
+	end
 	-- back from error_msg? then show the formspec again
 	if(fields.back_from_error_msg) then
 		yl_speak_up.show_fs(player, "action_evaluate", nil)
 		return
 	end
-	local pname = player:get_player_name()
-	local a_id = yl_speak_up.speak_to[pname].a_id
 	if(fields.back_to_talk) then
 		-- the action was aborted
 		yl_speak_up.execute_next_action(player, a_id, nil)
@@ -732,6 +741,7 @@ end
 yl_speak_up.get_fs_action_evaluate = function(player, param)
 	local pname = player:get_player_name()
 	local dialog = yl_speak_up.speak_to[pname].dialog
+	local n_id = yl_speak_up.speak_to[pname].n_id
 	local a = yl_speak_up.get_action_by_player(player)
 	if(not(a)) then
 		return ""