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#lang scheme/base
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; PARSEQ.PLT
;; A Parser Combinator library.
;;
;; Bonzai Lab, LLC. All rights reserved.
;;
;; Licensed under LGPL.
;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; util.ss - an utility module... the code might be moved out of here...
;; yc 12/31/2009 - first version
(require mzlib/etc
)
;; the-number
;; makes a function that returns a particular number no matter what
;; args are passed in
(define (the-number n)
(lambda args n))
;; bits->byte
;; convert a list of bits into its corresponding byte (or integer...)
;; note the byte can be greater than 255
(define (bits->byte bits)
(define (->i bit)
(case bit
((0 #f) 0)
((1 #t) 1)))
(apply +
(map (lambda (bit exponent)
(* (->i bit) (expt 2 exponent)))
bits
(reverse (build-list (length bits) identity)))))
;; byte->bits
;; the reverse of converting byte to bits...
(define (byte->bits b)
(define (helper q acc)
(cond ((= 0 q) acc)
(else
(let-values (((q r)
(quotient/remainder q 2)))
(helper q (cons r acc))))))
(helper b '()))
;; string-bytes/utf-8-length
;; return the bytes length for a string (instead of character length)
(define (string-bytes/utf-8-length s)
(bytes-length (string->bytes/utf-8 s)))
(provide (all-defined-out))
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