I was trying to define a "read-only" parameter, i.e. a parameter that can be "read" and "parameterized", but not "written". I'd want to call functions without being worried that the any of them changes that parameter, but I want to allow each function to parameterize the parameter for internal use.
Perhaps an "example" is clearer: ;----- #lang racket/base (require racket/port) (define my-curr-out-port (make-parameter (current-output-port))) (define (hello) (displayln "Hello" (my-curr-out-port))) (define (quietly) (parameterize ([my-curr-out-port (open-output-nowhere)]) (hello))) (define (mute) (my-curr-out-port (open-output-nowhere))) ; I'd want an error here. (hello) ;---> "Hello" (quietly) ;---> "" (hello) ;---> "Hello" (mute) (hello) ;---> "" :( ;--- Gustavo ____________________ Racket Users list: http://lists.racket-lang.org/users
