The vector contains all the constants, variable names and function names used by the function, except for certain primitives that are coded as special instructions. This command reads the defun containing point, compiles it, and evaluates the result. If you use this on a defun that is actually a function definition, the effect is to install a compiled version of that function. This function compiles a file of Lisp code named filename into a file of byte-code. The output file's name is made by appending c to the end of filename .
Compilation works by reading the input file one form at a time.
If it is a definition of a function or macro, the compiled function or macro definition is written out. Other forms are batched together, then each batch is compiled, and written so that its compiled code will be executed when the file is read. All comments are discarded when the input file is read. This command returns t . When called interactively, it prompts for the file name.