[racket] racket newbie question on quoting and the built in procedure-arity function

Perfect, I didn't know structs could be used like that.
Thank you!

As a follow-up question, can you directly create functions with a custom
printing method, without having to go through structs?


On Sat, Jan 4, 2014 at 8:13 PM, Vincent St-Amour <stamourv at ccs.neu.edu>wrote:

> Similarly, you can represent safe functions as applicable structures (so
> they can behave like functions) with a custom printing method.
>
>     #lang racket
>
>     (struct safe-function (f name)
>             #:property prop:procedure 0 ; first field is the function
>             #:methods gen:custom-write
>             [(define (write-proc safe-function port mode)
>                (display (safe-function-name safe-function) port))])
>
>     (define $+ (safe-function + '$+))
>
>     ($+ 1 2) ; => 3
>     $+ ; prints "$+"
>
>
> Vincent
>
>
>
> At Sat, 4 Jan 2014 18:52:55 -0500,
> Matthias Felleisen wrote:
> >
> > [1  <multipart/alternative (7bit)>]
> > [1.1  <text/plain; iso-8859-1 (quoted-printable)>]
> >
> > Perhaps you want something like this:
> >
> > Welcome to Racket v6.0.0.1.
> > > (current-print (lambda (x) (if (procedure? x) (printf "~a"
> (object-name x)) (print x)) (newline)))
> > #<void>
> > > +
> > +
> > > 10
> > 10
> >
> >
> >
> >
> > On Jan 4, 2014, at 6:40 PM, Rian Shams wrote:
> >
> > > Sorry for my lack of clarity.
> > >
> > > My question is about the output that is displayed from calling the
> function. For example, evaluating just
> > >
> > > >$+
> > > #<procedure:$+>
> > >
> > > The result I am looking for is
> > >
> > > >$+
> > > $+
> > >
> > > as opposed to
> > > #<procedure:$+>
> > >
> > > I am not sure whether this is just a formatting or renaming problem,
> or if it is possible to change what the interpreter displays in Dr.Racket?
> > >
> > > I am fairly new to Racket and programming in general and so I really
> appreciate your responses and patience.
> > >
> > >
> > > On Sat, Jan 4, 2014 at 5:49 PM, Matthias Felleisen <
> matthias at ccs.neu.edu> wrote:
> > >
> > > Yes, you need two functions: one that gives you the name of a
> procedure and one that picks a procedure. I was merely hinting at how to do
> the former. -- Matthias
> > >
> > >
> > >
> > > On Jan 4, 2014, at 4:57 PM, Rian Shams wrote:
> > >
> > >> Thanks Matthias,
> > >>
> > >> If I use your definition:
> > >>
> > >> (define (select-random-safe-function)
> > >>   (object-name
> > >>    (list-ref safe-function-set (random (length safe-function-set)))))
> > >>
> > >> then,
> > >>
> > >> >(procedure-arity (select-random-safe-function))
> > >> error:procedure-arity: contract violation
> > >>   expected: procedure?
> > >>   given: '$+
> > >>
> > >>
> > >> I believe I need two things:
> > >>
> > >> 1. (select-random-safe-function) should return an unquoted procedure,
> similar to
> > >>
> > >> (define (select-random-safe-function) ;without object-name
> > >>    (list-ref safe-function-set (random (length safe-function-set))))
> > >> >(select-random-safe-function)
> > >> #<procedure:$+>
> > >>
> > >> preferably without #<procedure: $+ >
> > >>
> > >> so my problem is that I want the output to display
> > >> $+
> > >> instead of
> > >> #<procedure:$+>
> > >>
> > >> 2. The reason the procedure needs to be unquoted is because
> > >> (procedure-arity (select-random-safe-function)) will produce an error
> if the function is quoted.
> > >>
> > >>
> > >>
> > >>
> > >> Later on I use both (procedure-arity (select-random-safe-function))
> and (select-random-safe-function) in a main function:
> > >>
> > >> ;;Generate Initial Population
> > >> ;population size is a positive integer and the auxiliary-function,
> generate-chromsome generates a tree using functions from safe-function-set
> and terms (numbers and symbols) from a term-set
> > >>
> > >> (define (generate-initial-population population-size)
> > >>   (cond [(zero? population-size) empty]
> > >>            [else (cons (generate-chromosome initial-chromosome-depth)
> ;initial-chromosome-depth is 3
> > >>                             (generate-initial-population (sub1
> population-size)))]))
> > >>
> > >> > (generate-initial-population 1)
> > >> '((#<procedure:$/> (#<procedure:$-> x .234) (#<procedure:$+> .576 x)))
> > >>
> > >> this gets me my desired result, but is hard for me to read especially
> as the depth and population size grows (typically I will be working with
> populations ranging in the hundreds or thousands and each chromosome/tree's
> depth could easily exceed 10) so it would be more convenient here if my
> solution displays
> > >>
> > >> '(($/ ($- x .234) ($+ .576 x)))
> > >>
> > >> instead of
> > >>
> > >> '((#<procedure:$/> (#<procedure:$-> x .234) (#<procedure:$+> .576 x)))
> > >>
> > >> and I am not sure how I would go about doing this?
> > >>
> > >> On Sat, Jan 4, 2014 at 8:45 AM, Matthias Felleisen <
> matthias at ccs.neu.edu> wrote:
> > >>
> > >> If you really just want the name, use object-name:
> > >>
> > >> (define (select-random-safe-function)
> > >>   (object-name
> > >>    (list-ref safe-function-set (random (length safe-function-set)))))
> > >>
> > >> Welcome to DrRacket, version 6.0.0.1--2013-12-29(bbb0c5f6/d) [3m].
> > >> Language: racket.
> > >> > (select-random-safe-function)
> > >> '$*
> > >>
> > >>
> > >>
> > >>
> > >> On Jan 4, 2014, at 2:48 AM, Rian Shams wrote:
> > >>
> > >>> If I do this I get the results I need for (procedure-arity
> (select-random-safe-function)), but when I call
> > >>> (safe-function-set) or (select-random-safe-function) or any other
> function that returns a safe function I get for example:
> > >>>
> > >>> >(safe-function-set)
> > >>> '(#<procedure:$+> #<procedure:$-> #<procedure:$*> #<procedure:$/>)
> > >>>
> > >>> >(select-random-safe-function)
> > >>> #<procedure:$->
> > >>>
> > >>> whereas when it was defined using quote as opposed to list I get:
> > >>>
> > >>> >(safe-function-set)
> > >>> '($+ $- $* $/)
> > >>>
> > >>> >(select-random-safe-function)
> > >>> '$-
> > >>>
> > >>> How would I get rid of this #<procedure:$-> part for readability,
> keeping only the $- part which is the actual function I defined, while
> still keeping it a function/procedure that gives me the function arity
> using (procedure-arity (select-random-safe-function))?
> > >>>
> > >>> Best,
> > >>>
> > >>>
> > >>> On Fri, Jan 3, 2014 at 5:31 PM, Sam Tobin-Hochstadt <
> samth at cs.indiana.edu> wrote:
> > >>> Try replacing `safe-function-set` with:
> > >>>
> > >>> (define safe-function-set (list $+ $- $* $/))
> > >>>
> > >>> Sam
> > >>>
> > >>> On Fri, Jan 3, 2014 at 5:28 PM, Rian Shams <rian.shams at gmail.com>
> wrote:
> > >>> > Hello,
> > >>> >
> > >>> > I am working with functions that I have defined to only take 1 or
> 2 operands
> > >>> > (called safe-functions) for the implementation of a genetic
> program.
> > >>> >
> > >>> > (define ($+ augend addend) ;operation is addition
> > >>> >   (+ augend addend)) ; the result is the sum
> > >>> > (define ($- minuend subtrahend) ;operation is subtraction
> > >>> >   (- minuend subtrahend)) ;result is difference
> > >>> > (define ($* multiplicand multiplier) ;operation is multiplication
> > >>> >   (* multiplicand multiplier)) ;result is product
> > >>> > (define ($/ dividend divisor) ;operation is division
> > >>> >   (/ dividend divisor)) ;result is quotient
> > >>> >
> > >>> > (define (infinity? x) (or (eq? x +Inf.0) (eq? x -Inf.0)))
> > >>> > (define ($sin x) (if (infinity? x) (* (sgn x) +Inf.0) (sin x)))
> > >>> > (define ($cos x) (if (infinity? x) (* (sgn x) +Inf.0) (cos x)))
> > >>> >
> > >>> > (define safe-function-set
> > >>> >   '($+
> > >>> >     $-
> > >>> >     $*
> > >>> >     $/
> > >>> >     ;$sin
> > >>> >     ;$cos))
> > >>> >
> > >>> > (define (select-random-safe-function)
> > >>> >   (list-ref safe-function-set (random (length safe-function-set))))
> > >>> >
> > >>> > I would like to use procedure-arity (or a similar function) to
> determine the
> > >>> > arity of a randomly selected safe function but I get this error:
> > >>> >
> > >>> >>(procedure-arity (select-random-safe-function))
> > >>> > error: procedure-arity: contract violation
> > >>> >   expected: procedure?
> > >>> >   given: '$+
> > >>> >
> > >>> > I think the problem is that the safe-functions are passed to
> procedure-arity
> > >>> > quoted. Is there a way I can unquote the functions, or adjust
> > >>> > procedure-arity to make (procedure-arity
> (select-random-safe-function))
> > >>> > work?
> > >>> >
> > >>> > Thanks,
> > >>> > --
> > >>> > Rian Shams
> > >>> >
> > >>> > ____________________
> > >>> >   Racket Users list:
> > >>> >   http://lists.racket-lang.org/users
> > >>> >
> > >>>
> > >>>
> > >>>
> > >>> --
> > >>> Rian Shams
> > >>> ____________________
> > >>>  Racket Users list:
> > >>>  http://lists.racket-lang.org/users
> > >>
> > >>
> > >>
> > >>
> > >> --
> > >> Rian Shams
> > >
> > >
> > >
> > >
> > > --
> > > Rian Shams
> >
> > [1.2  <text/html; iso-8859-1 (7bit)>]
> >
> > [2  <text/plain; us-ascii (7bit)>]
> > ____________________
> >   Racket Users list:
> >   http://lists.racket-lang.org/users
>



-- 
Rian Shams
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