@ben 1) thanks for the stickers, they’re great (already on laptop) 2) would def buy a Racket shirt from DevSwag or similar

Anyone with more FFI experience than me, I’ve written the following code using mmap(), but it always segfaults:

(define _mmap
  (get-ffi-obj 'mmap #f
               (_fun _pointer _ssize _int _int _int _int -> _pointer)))

(define (mmap f len)
  (define fp (open-input-file f))
  (_mmap #f len (bitwise-xor PROT_WRITE PROT_READ) MAP_SHARED (get_port_fd fp) 0))

(ptr-ref (mmap "/tmp/x" 100) _byte 0)

I assume I’m doing something wrong, but I don’t know what

@samth Trying using #:save-errno 'posix and (saved-errno); probably the OS reports an error

samth: taking a look now…. where can I import get_port_fd from?

For me, it’s EACCES, and using MAP_PRIVATE makes it succeed

(define get_port_fd (get-ffi-obj 'scheme_get_port_fd #f (_fun _racket -> _int)))

ah, using PROT_READ only makes it work

yeah, mmap returns –1 for your invocation

samth: use open-input-output-file instead of open-input-file

@thinkmoore I’ve tried that, but it gives me an error (with 25 as errno, which isn’t EACCES)

instead it appears to be ENOTTY which is very odd

@samth Does mmap return –1 in that case?

I don’t think so

I get 35 as the first byte of the file I’m reading (my source code itself), which is unicode for #

errno does happen to be set to 25

ah, ok

so it just sets errno wrongly

well, more likely just doesn’t set it at all

one last q: is the best way to check that the pointer returned by mmap is sensible is just (cast m _pointer _long) and see if it’s positive?

also, @thinkmoore @mflatt thanks for the help — now working

https://github.com/samth/mmap

Good morning all — In v6.8 is there a way to force DrRacket to open files in new windows? I can’t find the option :disappointed:

nevermind, found it :slightly_smiling_face:

If I have a class and inside I define a helper function using (define (helper a b) (+ a b)), how can I access this function from another module in order to test it?

@pocmatos There isn’t really a way to access that, it’s local to the class definition, but if you have methods or fields that use the helper function you can use those to test the behavior of the object and make sure helper works the way you expect

@dan shame there isn’t some kind of override, but thanks.

It’s basically the same reason that you can’t access a definition local to a function ie: (define (foo x y z) (define (helper a b) (+ a b)) (... some-expression-maybe-using-helper ...)) There’s no way to test that helper is correct inside of foo other than testing foo itself

Yes, I understand that however there are exceptions to accesses when testing, for example, you can do require/expose to access non provided members of a module. I had hoped there was something similar for local definitions. :slightly_smiling_face:

@pocmatos The require/expose form only works for modules, not helpers inside a function. In general it’s not possible to extract a locally defined helper because it might have closed over local variables that wouldn’t exist once you’ve extracted it. If your helper doesn’t depend on the local context it’s defined in, lift it into a regular module-level definition so you can test it

:wave: s back

what brought you to Racket from CL? If I may ask