;;;; srfi.27.weibulls.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.weibulls

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

(import scheme
  (chicken base)
  (chicken type)
  (only (type-checks-numbers scheme) check-real)
  (only type-checks-structured check-procedure)
  (srfi 27)
  srfi-27-distributions-support)

;;;

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

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

;;; Weibull distribution

(define (*make-random-weibulls shape scale randoms)
  (let ((invscale (*-reciprocal scale))
        (invshape (*reciprocal shape)) )
    (lambda () (expt (* invscale (log (- 1 (randoms)))) invshape)) ) )

(define (make-random-weibulls #!key (shape 1) (scale 1) (randoms (current-random-real)))
  (check-positive-real 'make-random-weibulls shape 'shape)
  (check-positive-real 'make-random-weibulls scale 'scale)
  (check-procedure 'make-random-weibulls randoms 'randoms)
  (values (*make-random-weibulls shape scale randoms)
          (lambda () (values shape scale randoms))) )

) ;module srfi.27.weibulls