This is the first Scheme program I had ever wrote; and its present form is the result of many kind folks helping me out :)

#lang scheme

(define mamort
 (lambda (bal pcnt pay)
   (format "Payment #,Payment Amount,Interest Paid,Principle
Paid,Balance,Total Interest~%")
   (amort bal pcnt pay 12)))

(define amort
 (lambda (bal pcnt pay freq)
   (let loop ((bal bal) (tot-int 0) (pmt 1))
     (let* ((int (* pcnt bal (/ freq)))
            (prin (min (- pay int) bal))
            (new-bal (- bal prin))
            (new-int (+ int tot-int))
            (done (< (+ int prin) pay)))
       (if done
           (printf "~s,~s,~s,~s,~s,~s~n"
                   pmt (+ int prin) int prin new-bal new-int)
           (begin
             (printf "~s,~s,~s,~s,~s,~s~n"
                     pmt pay int prin new-bal new-int)
             (loop new-bal new-int (+ 1 pmt))))))))

(mamort 10000 .12 350)

import Text.Printf

amortize :: Float -> Float -> Int -> [(Int, Float, Float, Float)]
amortize _ _ 0 = []
amortize b r l = (l - 1, prn, int, b') : amortize b' r (l - 1)
                 where int = b * r
                       prn = int / (1 - (1 + r) ^^ (-l)) - int
                       b' = b - prn

amortization :: Float -> Float -> Int -> IO ()
amortization b r l = do
    putStrLn "Left Principal Interest   Balance"
    mapM_ table $ (l, 0, 0, b) : amortize b (r / 12 / 100) l
    where table (m, p, i, t) = printf "%4d %9.2f %8.2f %9.2f\n" m p i t

main :: IO ()
main = amortization 10000 7 36