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 block argument is of type foreign-block-pointer.
The lambda list of the invoker is
inserts in front of the supplied
an additional argument for the block. Therefore a supplied
must not include an argument for the block. Similarly a supplied
in define-foreign-funcallable should not include an argument for the function.
LispWorks Foreign Language Interface User Guide and Reference Manual - 7 Dec 2011