CPS (NeWS)
C to PostScript: the NeWS stub compiler, which made PostScript procedures living in the window server callable as C macros and shipped the arguments down the connection.
A C program that wanted to draw in NeWS sent PostScript text to the server. Assembling those strings by hand was error-prone, so Sun supplied cps: in a .cps file you wrote cdef ps_moveto(x, y) x y moveto, and out came a C header with a ps_moveto macro that encoded the arguments compactly and appended them to the output buffer bound for the server. An arrow, =>, in a definition declared that the server would send something back, tagged so the client could wait for the right value.
It was remote procedure call in miniature, with the whole server as the address space: a stub could define a new class in the server just as easily as move a pen. The idea outlived NeWS. Adobe's Display PostScript got pswrap, which did exactly the same thing with defineps blocks, and NeXT programmers wrote wraps for a decade. By the TNT era it became more common to write the entire interface in PostScript and let the C side shrink.