: add ( seq seq -- seq )
    [ '[ swap _ [ H{ } clone or [ '[ swap _ at+ ] assoc-each ] keep ] change-at ] assoc-each ] keep ;

: weighted-choice ( chain key -- elem )
    swap at dup [ >alist [ swap ] assoc-map random-weighted* ] [ ] if ;
    
: add-line ( chain line -- chain )
    " " split 2 clump  [ first2 1 swap associate swap associate add ] each ;

: sentence ( chain word -- response )
    tuck 1 -rot [ dupd weighted-choice rot 1+ dup 15 < [ -rot ] dip dupd and ] [ dup ] [ 3drop ] produce " " join swap prefix " " join CHAR: . suffix ;