The other arguments are as for define-foreign-function
It defines the-name to be a function that can be used to invoke foreign blocks which takes arguments that match args. The block is then invoked by simply calling the function the-name with the block and arguments:
(the-name block arg1 arg2 ...)
The block argument is of type foreign-block-pointer.
The lambda list of the invoker is
). When lambda-list is supplied,
define-foreign-block-invoker inserts in front of the supplied lambda-list an additional argument for the block. Therefore a supplied lambda-list must not include an argument for the block. Similarly a supplied lambda-list in define-foreign-funcallable should not include an argument for the function.
LispWorks Foreign Language Interface User Guide and Reference Manual - 29 Sep 2017