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 <stamo...@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 < > matth...@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:$+> .576 x))) > > >> > > >> and I am not sure how I would go about doing this? > > >> > > >> On Sat, Jan 4, 2014 at 8:45 AM, Matthias Felleisen < > matth...@ccs.neu.edu> wrote: > > >> > > >> If you really just want the name, use object-name: > > >> > > >> (define (select-random-safe-function) > > >> (object-name > > >> (list-ref safe-function-set (random (length safe-function-set))))) > > >> > > >> Welcome to DrRacket, version 6.0.0.1--2013-12-29(bbb0c5f6/d) [3m]. > > >> Language: racket. > > >> > (select-random-safe-function) > > >> '$* > > >> > > >> > > >> > > >> > > >> 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 < > sa...@cs.indiana.edu> wrote: > > >>> Try replacing `safe-function-set` with: > > >>> > > >>> (define safe-function-set (list $+ $- $* $/)) > > >>> > > >>> Sam > > >>> > > >>> On Fri, Jan 3, 2014 at 5:28 PM, Rian Shams <rian.sh...@gmail.com> > wrote: > > >>> > Hello, > > >>> > > > >>> > I am working with functions that I have defined to only take 1 or > 2 operands > > >>> > (called safe-functions) for the implementation of a genetic > program. > > >>> > > > >>> > (define ($+ 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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