;;; 2.15b.scm
;;;
;;; $Id: 2.15b.scm 1.2 2024/12/07 12:12:25 s Exp $
;
; bc, Before-tax cash flow 
; nbc, nominal before-tax cash flow
; da,  Depletion
; ti,  Taxable income
; tax
; ac, After-tax cash flow
; tr, tax rate
; ir, infration rate
; ic, initial capital expenditure
; dr,  discount rate
; df, discount factor
; ny
; pvac, present value of ac
(use gauche.sequence)
(define (main args)
  ; procedure
  (define sum (lambda (x) (fold + 0 x)))

  ; input
  (define tr 0.34)
  (define ir 0.04)
  (define dr 0.12)
  (define ic 10e6)
  (define ny 5)
  (define bc   (list (- ic) 2990e3 2990e3 2990e3 2990e3 2990e3))
  (define da   (list 0 (/ ic ny) (/ ic ny) (/ ic ny) (/ ic ny) (/ ic ny)))
  (define keisen "")
  (define dash   "-")

  ; calculation
  (define infl_fac (map-with-index (lambda (i _) (expt (+ 1 ir) i)) bc))
  (define nbc      (map            (lambda (x y) (* x y)) infl_fac bc))
  (define ti       (map            (lambda (x y) (if (>= x y) (- x y) 0)) nbc da))
  (define tax      (map            (lambda (x)   (* x tr)) ti))
  (define ac       (map            (lambda (x y) (- x y))  nbc tax))
  (define df       (map-with-index (lambda (i _) (/ (expt (+ 1 dr) i))) bc))
  (define pvac     (map            (lambda (x y) (* x y)) ac df))
  (define sumpvac  (sum pvac))

  ; output
  (print "2.15b.scm")
  (format #t "~10@a~10@a~10@a~10@a~10@a~10@a~10@a~10@a~10@a~10@a\n"
             "year" "bc" "infl_fac" "nbc" "da" "ti" "tax" "ac" "df" "pvac")
  (for-each-with-index (lambda (i x1 x2 x3 x4 x5 x6 x7 x8 x9)
      (format #t "~10d~10d~10,3f~10d~10d~10d~10d~10d~10,3f~10d\n" 
                    i
        (x->integer x1) 
                    x2 
        (x->integer x3)
        (x->integer x4)
        (x->integer x5) 
        (x->integer x6) 
        (x->integer x7)
                    x8
        (x->integer x9)
      )
    ) 
    bc infl_fac nbc da ti tax ac df pvac
  )
  (format #t "~90@a~10d\n" "sum of pvac=" (x->integer sumpvac))
  (print "note")
  (print "bc: before-tax cash flow, infl_fac: inflation factor, nbc: nominal beforetax cash flow")
  (print "da: depletion, ti: taxable income, ac: after-tax cash flow, df: discount factor")
  (print "pvac: present value of after-tax cash flow")
0)
;;; end