Yes! This is exactly what I needed to know. (I suspected as much...my email earlier was in the midst of trying to figure out a huge type error I was getting (related to a bug report I sent in shortly after).)
Thanks! Best, jmj -- Sent from my Android phone with K-9 Mail. "J. Ian Johnson" <i...@ccs.neu.edu> wrote: >On a higher level note, if you're asking about the surrounding form for >the @ 0, this is what is called a filter - meaning what type >information do you learn if the output of the function tests to be >non-false and likewise for false. (left of | is then branch info, right >is else branch). > >If you test a number in an if, you will always go to the then branch. >Thus in the then branch you just know that whatever was given to the >function has the "not false" type. In the else branch you know the >input has the "false" type. This is useless information in the number >case, because Typed Racket already knows (Number @ 0) implies (! False >@ 0). > >-Ian >----- Original Message ----- >From: "Matthias Felleisen" <matth...@ccs.neu.edu> >To: "Jordan Johnson" <j...@fellowhuman.com> >Cc: users@racket-lang.org >Sent: Thursday, October 18, 2012 7:30:38 PM GMT -05:00 US/Canada >Eastern >Subject: Re: [racket] Meaning of "@" notation in TR > > >To elaborate on Ian's answer, TR can't use 'x' from the function >formals because x isn't in scope. So it has to use some other way of >saying '0th' argument, '1st' '2nd' etc. > > >On Oct 18, 2012, at 6:50 PM, Jordan Johnson wrote: > >> Hi all, >> >> I'm puzzled by this cryptic notation in Typed Racket (copied from the >docs): >> >> (λ: ([x : Number]) x) >> - : (Number -> Number : ((! False @ 0) | (False @ 0)) (0)) >> >> >> What does the "@ 0" mean? I have searched all of the TR doc pages, >but I see no explanation. >> >> Thanks, >> jmj >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users > > >____________________ > Racket Users list: > http://lists.racket-lang.org/users
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