ffi:call

(ffi:call address return-type argument-types args...)

Calls a C function at address with the given return type and argument-type list, marshalling each argument and the answer. The whole calling convention is decided at RUN time, which is what lets cffi:defcfun invent a shape in your program. Type designators are the CFFI keywords (:char .. :ullong, :float, :double, :pointer, :string, :void, :int8 .. :uint64), plus (:struct member...) for a structure by value and :varargs marking where a variadic tail starts.

A :string argument is copied into foreign memory for the call and freed after; a :string return reads the NUL-terminated UTF-8 back.