confusing warning from autoconf

[Mo DeJong]

Perhaps I am just doing something stupid here, but I just can
not figure out why autoconf is printing a warning for this
configure.in file.

% cat configure.in
AC_INIT(foo)


AC_DEFUN(FOO, [
    foo_cmd="$JAVAC $JAVAC_FLAGS Test.java"
    echo $foo_cmd
])

FOO

% autoconf
autoconf: undefined macros:
configure.in:5:    foo_cmd="$JAVAC $JAVAC_FLAGS Test.java"


Any ideas?

Mo Dejong
Red Hat Inc.