Mailing List Archive: 49091 messages
  • Home
  • Script library
  • AltME Archive
  • Mailing list
  • Articles Index
  • Site search

[REBOL] Re: Don't understand "try" and "disarm"

From: petr:krenzelok:trz:cz at: 14-Mar-2006 15:03

Hi Steven, a bit confusing, isn't it? In fact, some time ago, I just did the same mistake. I expected 'try to catch the error. Well, it does so, but it returns it. I don't like the way it work, but it is so, so let's just find some way out from it - ->> try [read %nonexistant.txt] ** Access Error: Cannot open /c/rebol/view/nonexistant.txt ** Near: read %nonexistant.txt ->> error? try [read %nonexistant.txt] == true You can see? 'try is there just to catch the error, but you still have to somehow maintain it. Single 'error? is enough for script not to crash, let's rewrite it a bit: ->> if error? try [read %nonexistant.txt][print "file does not exist"] file does not exist It seems to me, the error is returned from 'try call to the interpreter. We can "catch" it using 'disarm function: ->> probe disarm try [read %nonexistant.txt] make object! [ code: 500 type: 'access id: 'cannot-open arg1: "/c/rebol/view/nonexistant.txt" arg2: none arg3: none near: [read %nonexistant.txt] where: none ] I think you was not alone, who was a bit confused, so we've got some shortcuts in some later Core releases - 'attempt function: ->> attempt [read %nonexistant.txt] == none Attempt is a mezzanine function (defined in rebol): ->> source attempt attempt: func [ {Tries to evaluate and returns result or NONE on error.} value ][ if not error? set/any 'value try :value [get/any 'value] ] I hope you can proceed from that further .... Cheers, -pekr-