Lookahead-* procedures mutate port position.

[Takashi Kato]

This should return (#\a 0 #\b) but (#\a 1 #\a)

(define in (open-string-input-port "ab"))

(let* ((c0 (peek-char in))
       (pos (port-position in))
       (c1 (begin
             (set-port-position! in 1)
             (read-char in))))
  (list c0 pos c1))

[Takashi Kato]

It turned out that both binary and textual ports peeked port position handling is incorrect. The following script shows wrong results:

#!r6rs
(import (rnrs))

(define (print . args) (for-each display args) (newline))

(define (test-port in peek read)
  (print
   (let* ((c0 (peek in))
          (pos (port-position in))
          (c1 (begin
                (set-port-position! in 1)
                (read in))))
     (list c0 pos c1)) ))
(test-port (open-string-input-port "ab") peek-char read-char)
(test-port (open-bytevector-input-port #vu8(1 2)) lookahead-u8 get-u8)

[Takashi Kato]

Considering peeked buffer during returning port position (Fixes #184)

→ <<cset 9b05f1639723>>