define prepend
    $prepend_val !
    $prepend_phrase !
    '[ $prepend_val @ $prepend_phrase @ unphrase '] phrase
    $prepend_val forget $prepend_phrase forget
    ;

define append
    $append_val !
    $append_phrase !
    '[ $append_phrase @ unphrase $append_val @ '] phrase
    $append_val forget $append_phrase forget
    ;

[ 2 3 ] 1 prepend .
[ 2 3 ] 4 append .
[ 1 2 3 ] pop . .