From Xojo Documentation
IsFunctionAvailable will attempt to load the passed function from the specified library.
If the function can be loaded, IsFunctionAvailable returns True. If the operation fails, it returns False. Calling IsFunctionAvailable or using the Soft keyword in a Declare statement will cache both the library loading code as well as the function itself. Multiple calls to the same function will suffer almost no overhead costs in comparison to regular ("hard") Declares. See the description of Soft Declares in the notes for the Declare statement.