Backtrace:
           5 (primitive-load "/gnu/store/hjc7n3s77yb6q24jvaxmbchclg7?")
In ice-9/eval.scm:
   196:43  4 (_ #f)
In srfi/srfi-1.scm:
   691:23  3 (filter-map #<procedure configuration-sub-directory ?> . #)
In ice-9/eval.scm:
    159:9  2 (_ #(#(#<directory (guile-user) 7ffff7812c80>) (# # ?)))
In srfi/srfi-1.scm:
   586:17  1 (map1 ("/lib/udev/hwdb.d" "/libexec/udev/hwdb.d"))
In unknown file:
           0 (string-append (begin udev-rule "90-spoof-eth0-mac.?" ?) ?)

ERROR: In procedure string-append:
In procedure string-append: Wrong type (expecting string): (begin udev-rule "90-spoof-eth0-mac.rules" (string-append "ACTION==\"add\", SUBSYSTEM==\"net\", " "ATTR{address}==\"b8:27:eb:15:61:71\", " "RUN+=\"" "/gnu/store/4pbaxbbrl87g4nr3x1hw35j1kyn7zcp3-iproute2-6.4.0" "/sbin/ip link set dev eth0 address b0:25:aa:46:63:d6\""))