> (define (upcase-all in) (for ([l (in-lines in)]) (display (string-upcase l)) (newline)))
> (upcase-all (open-input-string (string-append "Hello, World!\n" "Can you hear me, now?")))
CAN YOU HEAR ME, NOW?
If you want to determine whether “hello” appears in a file, then you could search separate lines, but it’s even easier to simply apply a regular expression (see Regular Expressions) to the stream:
> (define (has-hello? in) (regexp-match? #rx"hello" in)) > (has-hello? (open-input-string "hello"))
> (has-hello? (open-input-string "goodbye"))
If you want to copy one port into another, use copy-port from racket/port, which efficiently transfers large blocks when lots of data is available, but also transfers small blocks immediately if that’s all that is available:
> (define o (open-output-string)) > (copy-port (open-input-string "broom") o) > (get-output-string o)