good point, thanks.
On Fri, Mar 7, 2014 at 1:18 PM, Jens Axel Søgaard <jensa...@soegaard.net>wrote: > Error messages use the name reported by object-name. > > 2014-03-07 13:11 GMT+01:00 Laurent <laurent.ors...@gmail.com>: > > Is this really a need? I really wouldn't bother to have > >> (object-name empty?) > > 'null? > > > > (I have no strong opinion on the subject though, I'm just wondering if > there > > is a pratical different too) > > > > Laurent > > > > > > > > On Fri, Mar 7, 2014 at 12:27 PM, Jens Axel Søgaard < > jensa...@soegaard.net> > > wrote: > >> > >> The (define (empty? l) (null? l)) is needed due to object-name. > >> > >> > (object-name null?) > >> 'null? > >> > (object-name empty?) > >> 'empty? > >> > (define my-empty? empty?) > >> > (object-name my-empty?) > >> 'empty? > >> > >> /Jens Axel > >> > >> > >> 2014-03-07 12:19 GMT+01:00 Ryan Davis <zenspi...@gmail.com>: > >> > > >> > On Mar 7, 2014, at 2:45, Daniel Carrera <dcarr...@gmail.com> wrote: > >> > > >> >> Hello, > >> >> > >> >> Is there any difference between `first` and `car`, or between `last` > >> >> and `cdr`, or between `empty? and null?` ? > >> >> > >> >> I had assumed that these were just synonyms, added by Racket because > >> >> they might be more memorable to a student. But apparently Racket > doesn't > >> >> think they are equal: > >> >> > >> >> -> (equal? first car) > >> >> #f > >> >> -> (equal? last cdr) > >> >> #f > >> >> -> (equal? empty? null?) > >> >> #f > >> >> > >> >> > >> >> I suppose that they could be separate functions that happen to do the > >> >> same thing, but if so, my next question would be why they aren't just > >> >> aliases. As in: > >> >> > >> >> -> (define myfirst car) > >> >> -> (equal? myfirst car) > >> > > >> > For many/most things in racket, you can bring up the definition for > >> > something inside of DrRacket: > >> > > >> > (define (first x) > >> > (if (and (pair? x) (list? x)) > >> > (car x) > >> > (raise-argument-error 'first "(and/c list? (not/c empty?))" x))) > >> > > >> > I couldn't for car, so I'm assuming it is considered a primitive. > >> > > >> > last and cdr aren't synonymous: > >> > > >> > (define (last l) > >> > (if (and (pair? l) (list? l)) > >> > (let loop ([l l] [x (cdr l)]) > >> > (if (pair? x) > >> > (loop x (cdr x)) > >> > (car l))) > >> > (raise-argument-error 'last "(and/c list? (not/c empty?))" l))) > >> > > >> > > >> > (define (empty? l) (null? l)) > >> > > >> > null? seems to be a primitive as well. Not sure why they're not direct > >> > synonyms in this case. > >> > > >> > > >> > ____________________ > >> > Racket Users list: > >> > http://lists.racket-lang.org/users > >> > >> > >> > >> -- > >> -- > >> Jens Axel Søgaard > >> > >> ____________________ > >> Racket Users list: > >> http://lists.racket-lang.org/users > > > > > > > > -- > -- > Jens Axel Søgaard >
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