11.6.1.2480 WRITE-FILE FILE
( c-addr u fileid -- ior )
Write u characters from c-addr to the file identified by fileid starting at its current position. ior is the implementation-defined I/O result code.
At the conclusion of the operation, FILE-POSITION returns the next file position after the last character written to the file, and FILE-SIZE returns a value greater than or equal to the value returned by FILE-POSITION.