;;;; srfi.27.paretos.scm
;;;; Kon Lovett, Dec '17
;;;; Kon Lovett, Jun '17
;;;; Kon Lovett, May '06

; Chicken Generic Arithmetic! (would use fp routines, except for the "real" constraint)

(module srfi.27.paretos

(;export
  *make-random-paretos
  make-random-paretos)

(import scheme
  (chicken base)
  (chicken type)
  (only type-errors error-argument-type)
  (only type-checks
    define-check+error-type
    check-procedure
    check-natural-integer
    check-real
    check-open-interval
    check-closed-interval)
  (srfi 27)
  srfi-27-distributions-support
  (srfi 27 gammas)
  (srfi 27 exponentials))

;;;

(include "srfi-27-common-types")

(: *make-random-paretos (number number random-real-function -> number-function))
(: make-random-paretos (#!rest -> number-function procedure))

;;; Pareto distribution

(define (*make-random-paretos alpha xmin randoms)
  (let ((gammas (*make-random-gammas alpha (*reciprocal xmin) randoms)))
    (*make-random-exponentials 1 (lambda () (*reciprocal (+ xmin (gammas)))))) )

(define (make-random-paretos #!key (alpha 1) (xmin 1) (randoms (current-random-real)))
  (check-positive-real 'make-random-paretos alpha 'alpha)
  (check-positive-real 'make-random-paretos xmin 'xmin)
  (check-procedure 'make-random-paretos randoms 'randoms)
  (values
    (*make-random-paretos alpha xmin randoms)
    (lambda () (values alpha xmin randoms))) )

) ;module srfi.27.paretos