Hello.
I think I understand how memq, memv, member works:
> (memq 'y '(y yes n no))
'(y yes n no)
> (memq 'n '(y yes n no))
'(n no)
> (memq 'racket '(y yes n no))
#f
>
By the way, I wrote a procedure as follows:
(require srfi/13)
(define (yes-or-no? arg)
; expected it returns #t or #f
; depending on input such as yes or no
(letrec ((y-or-n?
; if argument is either Y or YES,
; it returns #t otherwise #f
(lambda (sym)
(and (memq sym '(Y YES)) #t)))
(symbol-upcase
; confirm any symbol into uppercase
(lambda (arg)
(if (symbol? arg)
(string->symbol (string-upcase (symbol->string arg)))
(yes-or-no? (read))))))
(let ((sym (symbol-upcase arg)))
(if (memq sym '(Y YES N NO))
(y-or-n? sym)
(yes-or-no? (read))))))
I expected that (cond ((I input y or yes) returns #t)
((I input n or no) returns #f)
(else this procedure waits something))
However, result is sooooo strange:
> (yes-or-no? (read))
3
2
4
foo
bar
baz
yes
y
no
n
#f
Notice that even though yes, y or no is entered, the procedure ignores and
it never returns #f until n is entered.
Strange.
Does anyone know why this doesn't work?
Thanks.
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