Currently LSL code such as below does not compile on OpenSim, but compiles fine in Second Life:
list mylist = [];
mylist += [1, 2, 3];
mylist += "four";
list newlist = mylist + 5.0;
The problem is that the LSL_Types.list class does not have an operator for adding a string to a list.
I am including a patch which implements adding a string, integer or float to a list.
I am also including tests. The file LSL_TypesTestList.cs belongs in
OpenSim/Tests/OpenSim/Region/ScriptEngine/Common/.