USING: io kernel math math.parser ;
IN: payments

: interest-rate ( -- rate )
    .02 12 / ;

: initial-balance
    500 ;

: total-to-pay
    587 ;

: number-of-payments
    6 ;

: monthly-payment ( -- payment )
    total-to-pay number-of-payments / ;

: collect-interest ( balance -- new-balance )
    dup interest-rate * + ;

: payment ( balance -- new-balance )
    collect-interest monthly-payment - ;

: do-it ( -- )
    initial-balance number-of-payments [ payment ] times
    number>string print ;

MAIN: do-it