eval-when-compile

eval-when-compile is a Lisp macro in `byte-run.el'.

(eval-when-compile &rest BODY)

Like `progn', but evaluates the body at compile time if you're compiling.
Thus, the result of the body appears to the compiler as a quoted
constant. In interpreted code, this is entirely equivalent to
`progn', except that the value of the expression may be (but is
not necessarily) computed at load time if eager macro expansion
is enabled.