<div dir="ltr">Perfect, I didn't know structs could be used like that.<div>Thank you!</div><div> </div><div>As a follow-up question, can you directly create functions with a custom printing method, without having to go through structs?</div> </div><div class="gmail_extra"> <div class="gmail_quote">On Sat, Jan 4, 2014 at 8:13 PM, Vincent St-Amour <<a href="mailto:stamourv@ccs.neu.edu" target="_blank">stamourv@ccs.neu.edu</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">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)>] <div><div class="h5">> > 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 <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> 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:$+> .576 x))) > >> > >> and I am not sure how I would go about doing this? > >> > >> On Sat, Jan 4, 2014 at 8:45 AM, Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> wrote: > >> > >> If you really just want the name, use object-name: > >> > >> (define (select-random-safe-function) > >> (object-name > >> (list-ref safe-function-set (random (length safe-function-set))))) > >> > >> Welcome to DrRacket, version 6.0.0.1--2013-12-29(bbb0c5f6/d) [3m]. > >> Language: racket. > >> > (select-random-safe-function) > >> '$* > >> > >> > >> > >> > >> 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 <<a href="mailto:samth@cs.indiana.edu">samth@cs.indiana.edu</a>> wrote: > >>> Try replacing `safe-function-set` with: > >>> > >>> (define safe-function-set (list $+ $- $* $/)) > >>> > >>> Sam > >>> > >>> On Fri, Jan 3, 2014 at 5:28 PM, Rian Shams <<a href="mailto:rian.shams@gmail.com">rian.shams@gmail.com</a>> wrote: > >>> > Hello, > >>> > > >>> > I am working with functions that I have defined to only take 1 or 2 operands > >>> > (called safe-functions) for the implementation of a genetic program. > >>> > > >>> > (define ($+ 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: > >>> > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> > >>> > > >>> > >>> > >>> > >>> -- > >>> Rian Shams > >>> ____________________ > >>> Racket Users list: > >>> <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> > >> > >> > >> > >> > >> -- > >> Rian Shams > > > > > > > > > > -- > > Rian Shams > </div></div>> [1.2 <text/html; iso-8859-1 (7bit)>] > > [2 <text/plain; us-ascii (7bit)>] <div class="HOEnZb"><div class="h5">> ____________________ > Racket Users list: > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </div></div></blockquote></div> <div> </div>-- Rian Shams </div>