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;;; R7RS-PNM --- Library for reading and writing PNM (Portable Any Map) files for R7RS
;;; Copyright © 2024 Masaya Tojo <masaya@tojo.tokyo>
;;;
;;; This file is part of R7RS-PNM.
;;;
;;; R7RS-PNM is free software: you can redistribute it and/or modify it
;;; under the terms of the GNU Lesser General Public License as published
;;; by the Free Software Foundation, either version 3 of the License, or
;;; (at your option) any later version.
;;;
;;; R7RS-PNM is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;;; GNU Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public License
;;; along with R7RS-PNM. If not, see <https://www.gnu.org/licenses/>.
(define-library (image-format pnm private checker)
(export make-xy-checker
make-value-checker
make-boolean-value-checker)
(import (scheme base)
(scheme case-lambda)
(image-format pnm image))
(begin
(define (make-xy-checker width height)
(lambda (x y)
(when (or (not (exact-integer? x))
(< x 0)
(<= width x))
(error (string-append "`x` must be an integer such that 0 <= `x` < "
(number->string width))
x))
(when (and (not (exact-integer? y))
(< y 0)
(<= height y))
(error (string-append "`y` must be an integer such that 0 <= `y` < "
(number->string width))
y))))
(define (make-value-checker maxval sym)
(define message
(string-append "`" (symbol->string sym) "`"
" must be an integer such that 0 < "
"`" (symbol->string sym) "`"
" < "
(number->string maxval)))
(lambda (v)
(when (or (not (exact-integer? v))
(< v 0)
(< maxval v))
(error message v))))
(define (make-boolean-value-checker)
(lambda (v)
(when (not (boolean? v))
(error "`v` must be a boolean value" v))))
(define (split-value v)
(values (modulo (quotient v 256) 256)
(modulo v 256)))
(define (combine-values l r)
(+ (* 256 l) r))))
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