It encapsulates symbol lookup, possibly searching multiple libraries for a function. But that's not all: by wrapping Ffidl callout into an auto-generated Tcl procedure, it provides additional argument types that are pre-processed and post-processed before and after callout.
ffix also included some commands to manage in-memory buffers, thus allowing you to use functions with deferred input/output. This relies on Roger E Critchlow's Ffidl 0.6 (stubsymbol), while the other parts of ffix may work with Ffidl 0.5
This initial release of ffix is highly experimental and subject to changes in the API.