Re: [racket-users] Recursevly processing a list with "wholes"
Hi Justin, thanks for reply and the code! :) Cheers Meino Justin Zamora[16-11-17 04:02]: > I think you are looking for something like this: > > #lang racket > > (require test-engine/racket-tests) > > (define (remove-empty-lists lst) > (cond > [(null? lst) '()] ; Check for end of list > [(null? (first lst)) (remove-empty-lists (rest lst))] ; Skip null > sublist > [(not (list? (first lst))) ; Leave non-lists alone > (cons (first lst) (remove-empty-lists (rest lst)))] > [else ; Process the sublists recursively > (cons (remove-empty-lists (first lst)) >(remove-empty-lists (rest lst)))])) > > (check-expect (remove-empty-lists '()) '()) > (check-expect (remove-empty-lists '(a)) '(a)) > (check-expect (remove-empty-lists '(a b c)) '(a b c)) > (check-expect (remove-empty-lists '(())) '()) > (check-expect (remove-empty-lists '(() a)) '(a)) > (check-expect (remove-empty-lists '(a ())) '(a)) > (check-expect (remove-empty-lists '(a (b () c) d)) '(a (b c) d)) > (check-expect (remove-empty-lists '((a) (b c) () (e () f (g ())) h (() i > j))) > '((a) (b c) (e f (g)) h (i j))) > (test) > > Justin > > On Tue, Nov 15, 2016 at 10:52 PM, wrote: > > > Hi, > > > > I have a list of sublists. Some of the sublists are empty. > > The list should be processed recursevly and the resulting > > list should no longer contain empty sublists. > > > > The code I have so far looks like: > > > > (define (step-through-list lst) > > (if (empty? lst) > > lst > > (cons (process-sublist (car lst)) (step-through-list (cdr lst))) > > > > but "car" would feed empty sublists to process-sublist as any other > > sublist. How can I "silently" skip empty sublists and even get out of > > the recursion without harm (if the last sublist is empty) without > > switching to iteration? > > Is there something like "car-not-empty" ? ;) > > Or do I oversee the obvious here...? ;))) > > > > Thank you vary much for any help in advance! > > Cheers > > Meino > > > > > > -- > > You received this message because you are subscribed to the Google Groups > > "Racket Users" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to racket-users+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. > > > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] syntax-class composed of literals
On 11/16/2016 08:24 PM, Dan Liebgold wrote: FWIW, Eric Dobson wrote a very nice `define-literal-syntax-class` macro that is used extensively inside TR. https://github.com/racket/typed-racket/blob/master/typed-racket-lib/typed-racket/utils/literal-syntax-class.rkt Hmm... I can't quite figure that one out. Maybe with some examples? How does the ":spec" in the pattern work? It's just a class specified Suppose you have (define-syntax-class sc #:attributes (a b) ) The pattern x:sc or (~var x sc) binds x, x.a, and x.b. The pattern :sc or (~var || sc) binds just a and b (no prefix). The pattern _:sc or (~var _ sc) binds nothing. Note that || is a way of writing the 0-length identifier in Racket. Ryan -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] syntax-class composed of literals
On 11/16/2016 07:51 PM, Vincent St-Amour wrote: FWIW, Eric Dobson wrote a very nice `define-literal-syntax-class` macro that is used extensively inside TR. https://github.com/racket/typed-racket/blob/master/typed-racket-lib/typed-racket/utils/literal-syntax-class.rkt Its companion `define-merged-syntax-class` is quite nice too. https://github.com/racket/typed-racket/blob/master/typed-racket-lib/typed-racket/optimizer/utils.rkt#L110 I've used those in other projects as well, and like them a lot. Ryan: Would you consider adding them (or something like them) to syntax/parse? I could add a `#:define-syntax-class name` option to `define-literal-set` that would additionally define `name` as a syntax-class matching any of the literals. I would want to wait to add that until I implement the backtracking-aware handling of disappeared-uses, which I just haven't gotten to yet. For `define-merged-syntax-class`, I don't think I would put it in core syntax/parse, but maybe as a library in syntax/parse/lib/*. Ryan -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] syntax-class composed of literals
On 11/16/2016 07:42 PM, Dan Liebgold wrote: Literal sets can include datum-literals: (define-literal-set lits #:datum-literals (a b c) (d e)) Ah, oops I missed that keyword parameter. For question 1, that's probably the best way. If you want to suppress the printing of all of the datum literals in error messages, you can mark the syntax class as `#:opaque`. I was more wanting to avoid keeping two lists of the literals in the source... I *do* want the error to enumerate possibilities. In principle, you could also use `literal-set->predicate`, but I just discovered it ignores the datum literals. I'll push a fix. I saw that... assuming it worked, I'm not sure how/where I would put that.. Something like this: (define-literal-set var-type-lits ) (define-syntax-class var-type (pattern x:id #:fail-unless ((literal-set->predicate var-type-lits) #'x) "unrecognized var-type")) But then you wouldn't get the enumeration of the literals in errors either. Ryan -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] If a thunk is a proc of zero arguments, what is a proc of one argument?
Ah, I should have thought of that. Yep, it works. Thanks. On Wed, Nov 16, 2016 at 5:12 PM, Greg Hendershottwrote: > racket-mode is on MELPA: > > https://melpa.org/#/racket-mode > > But not MELPA stable. > > Personally I use only MELPA non-stable, because I like packages to > break all the time. Seriously, it's been fine, for me. > > In Emacs 24.4+ I understand it's possible to use both. You can say to > get certain packages from one or the other, using > `package-pinned-packages`, as explained here: > > http://stackoverflow.com/questions/38632453/how-should- > i-work-with-melpa-and-melpa-stable-using-emacs/38648126 > > Also even in older Emacs as explained here under "Customizations": > > https://melpa.org/#/getting-started > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Recursevly processing a list with "wholes"
I think you are looking for something like this: #lang racket (require test-engine/racket-tests) (define (remove-empty-lists lst) (cond [(null? lst) '()] ; Check for end of list [(null? (first lst)) (remove-empty-lists (rest lst))] ; Skip null sublist [(not (list? (first lst))) ; Leave non-lists alone (cons (first lst) (remove-empty-lists (rest lst)))] [else ; Process the sublists recursively (cons (remove-empty-lists (first lst)) (remove-empty-lists (rest lst)))])) (check-expect (remove-empty-lists '()) '()) (check-expect (remove-empty-lists '(a)) '(a)) (check-expect (remove-empty-lists '(a b c)) '(a b c)) (check-expect (remove-empty-lists '(())) '()) (check-expect (remove-empty-lists '(() a)) '(a)) (check-expect (remove-empty-lists '(a ())) '(a)) (check-expect (remove-empty-lists '(a (b () c) d)) '(a (b c) d)) (check-expect (remove-empty-lists '((a) (b c) () (e () f (g ())) h (() i j))) '((a) (b c) (e f (g)) h (i j))) (test) Justin On Tue, Nov 15, 2016 at 10:52 PM,wrote: > Hi, > > I have a list of sublists. Some of the sublists are empty. > The list should be processed recursevly and the resulting > list should no longer contain empty sublists. > > The code I have so far looks like: > > (define (step-through-list lst) > (if (empty? lst) > lst > (cons (process-sublist (car lst)) (step-through-list (cdr lst))) > > but "car" would feed empty sublists to process-sublist as any other > sublist. How can I "silently" skip empty sublists and even get out of > the recursion without harm (if the last sublist is empty) without > switching to iteration? > Is there something like "car-not-empty" ? ;) > Or do I oversee the obvious here...? ;))) > > Thank you vary much for any help in advance! > Cheers > Meino > > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] syntax-class composed of literals
> FWIW, Eric Dobson wrote a very nice `define-literal-syntax-class` macro > that is used extensively inside TR. > > > https://github.com/racket/typed-racket/blob/master/typed-racket-lib/typed-racket/utils/literal-syntax-class.rkt > Hmm... I can't quite figure that one out. Maybe with some examples? How does the ":spec" in the pattern work? It's just a class specified The examples in TR seem to declare classes one literal at a time? > Its companion `define-merged-syntax-class` is quite nice too. > > > https://github.com/racket/typed-racket/blob/master/typed-racket-lib/typed-racket/optimizer/utils.rkt#L110 > I was just looking for exactly that... very useful. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] If a thunk is a proc of zero arguments, what is a proc of one argument?
racket-mode is on MELPA: https://melpa.org/#/racket-mode But not MELPA stable. Personally I use only MELPA non-stable, because I like packages to break all the time. Seriously, it's been fine, for me. In Emacs 24.4+ I understand it's possible to use both. You can say to get certain packages from one or the other, using `package-pinned-packages`, as explained here: http://stackoverflow.com/questions/38632453/how-should-i-work-with-melpa-and-melpa-stable-using-emacs/38648126 Also even in older Emacs as explained here under "Customizations": https://melpa.org/#/getting-started -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] syntax-class composed of literals
FWIW, Eric Dobson wrote a very nice `define-literal-syntax-class` macro that is used extensively inside TR. https://github.com/racket/typed-racket/blob/master/typed-racket-lib/typed-racket/utils/literal-syntax-class.rkt Its companion `define-merged-syntax-class` is quite nice too. https://github.com/racket/typed-racket/blob/master/typed-racket-lib/typed-racket/optimizer/utils.rkt#L110 I've used those in other projects as well, and like them a lot. Ryan: Would you consider adding them (or something like them) to syntax/parse? Vincent On Wed, 16 Nov 2016 17:11:26 -0600, Dan Liebgold wrote: > > Hi, > > A couple questions about literals in syntax-parse: > > 1. I'd like to make a syntax-class that is just a set of literals (with a > clear error for something not matching any literal). Is there a better way > than this: > > http://pasterack.org/pastes/86722 > > I need to ignore the bindings for those identifiers, and I need to preserve > the syntax context. > > 2. Is there any plan or easy way to implement #:datum-literal-sets for > syntax-classes? It'd be nice to share a list of literals (with ignored > bindings) among multiple classes. > > Thanks, > Dan > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] syntax-class composed of literals
> > Literal sets can include datum-literals: > >(define-literal-set lits #:datum-literals (a b c) (d e)) > Ah, oops I missed that keyword parameter. > For question 1, that's probably the best way. If you want to suppress > the printing of all of the datum literals in error messages, you can > mark the syntax class as `#:opaque`. > I was more wanting to avoid keeping two lists of the literals in the source... I *do* want the error to enumerate possibilities. > In principle, you could also use `literal-set->predicate`, but I just > discovered it ignores the datum literals. I'll push a fix. > I saw that... assuming it worked, I'm not sure how/where I would put that.. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] syntax-class composed of literals
On 11/16/2016 06:11 PM, Dan Liebgold wrote: Hi, A couple questions about literals in syntax-parse: 1. I'd like to make a syntax-class that is just a set of literals (with a clear error for something not matching any literal). Is there a better way than this: http://pasterack.org/pastes/86722 I need to ignore the bindings for those identifiers, and I need to preserve the syntax context. 2. Is there any plan or easy way to implement #:datum-literal-sets for syntax-classes? It'd be nice to share a list of literals (with ignored bindings) among multiple classes. Literal sets can include datum-literals: (define-literal-set lits #:datum-literals (a b c) (d e)) For question 1, that's probably the best way. If you want to suppress the printing of all of the datum literals in error messages, you can mark the syntax class as `#:opaque`. In principle, you could also use `literal-set->predicate`, but I just discovered it ignores the datum literals. I'll push a fix. Ryan -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[racket-users] syntax-class composed of literals
Hi, A couple questions about literals in syntax-parse: 1. I'd like to make a syntax-class that is just a set of literals (with a clear error for something not matching any literal). Is there a better way than this: http://pasterack.org/pastes/86722 I need to ignore the bindings for those identifiers, and I need to preserve the syntax context. 2. Is there any plan or easy way to implement #:datum-literal-sets for syntax-classes? It'd be nice to share a list of literals (with ignored bindings) among multiple classes. Thanks, Dan -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Recursevly processing a list with "wholes"
Hi David, thanks for the reply and the link! :) I have a list of sublist, which I want to process recursively. Some sublists are empty, some are filled. The typical pattern is (as far as I know) (define (process-list lst) (cons (do-somthing-with-sublist (car lst)) (process-lst (car lst But this has the drawback, that empty sublists (via 'car lst') are processed also. So I need a "kind of car" which returns not the next sublist but the next not-empty sublist and skipping any empty sublist without breaking the recursion. Others on the list already posted some solutions for what I try to acchieve and this is only to clearify things. Is it now understandable, what I try to acchieve? Cheers Meino David Storrs[16-11-16 20:16]: > Hi Meino, > > As a suggestions, you might want to read through this page on Stack > Overflow about how to ask technical questions: > http://stackoverflow.com/help/how-to-ask The summary is: tell us what > you're trying to achieve, what you've tried, and what *specifically* is not > working. > > The question you're asking here (about walk-lists) is hard to help with, > because it's not clear what the context is. I'll take my best shot, though: > > On Wed, Nov 16, 2016 at 10:04 AM, wrote: > > > Hi John, > > > > thank you for your reply ! :) > > > > ...no, not a homework... > > I want to teach myself some racket and hope 'to get it' finally... > > Since I am no native speaker I have the deficulty to search for > > things, which names I dont know... > > > > One example of my code is: > > > > (define (trim-list lst) > > (if (empty? lst) > > lst > > (cons (string-trim (car lst)) (trim-list (cdr lst) > > > > > > (define (walk-sublists lst) > > (if (empty? lst) > > lst > > (cons (trim-list (car lst)) (walk-sublists (cdr lst) > > > > I want to avoid to call trim-list, if 'car lst' returns an empty list. > > Instead 'car lst' sghould return the next non-empty list... > > > > I will take a look in the reference manual for 'filter' and 'compose'. > > > > Cheers > > Meino > > > > > > > You might try something like this: > > (define (trim-list lst) > (if (empty? lst) > lst > (cons (string-trim (car lst)) > (trim-list (cdr lst) > > > > > > > > > > 'John Clements' via Racket Users > > [16-11-16 18:26]: > > > > > > > On Nov 15, 2016, at 19:52, meino.cra...@gmx.de wrote: > > > > > > > > Hi, > > > > > > > > I have a list of sublists. Some of the sublists are empty. > > > > The list should be processed recursevly and the resulting > > > > list should no longer contain empty sublists. > > > > > > Is this homework? > > > > > > if so: can you show your test cases? > > > > > > if not: (filter (compose not null?) l). > > > > > > > > > John Clements > > > > > > > > > > > The code I have so far looks like: > > > > > > > > (define (step-through-list lst) > > > >(if (empty? lst) > > > >lst > > > >(cons (process-sublist (car lst)) (step-through-list (cdr lst))) > > > > > > > > but "car" would feed empty sublists to process-sublist as any other > > > > sublist. How can I "silently" skip empty sublists and even get out of > > > > the recursion without harm (if the last sublist is empty) without > > > > switching to iteration? > > > > Is there something like "car-not-empty" ? ;) > > > > Or do I oversee the obvious here...? ;))) > > > > > > > > Thank you vary much for any help in advance! > > > > Cheers > > > > Meino > > > > > > > > > > > > -- > > > > You received this message because you are subscribed to the Google > > Groups "Racket Users" group. > > > > To unsubscribe from this group and stop receiving emails from it, send > > an email to racket-users+unsubscr...@googlegroups.com. > > > > For more options, visit https://groups.google.com/d/optout. > > > > > > > > > > > > -- > > > You received this message because you are subscribed to the Google > > Groups "Racket Users" group. > > > To unsubscribe from this group and stop receiving emails from it, send > > an email to racket-users+unsubscr...@googlegroups.com. > > > For more options, visit https://groups.google.com/d/optout. > > > > > > > -- > > You received this message because you are subscribed to the Google Groups > > "Racket Users" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to racket-users+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. > > > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails
Re: [racket-users] Recursevly processing a list with "wholes"
On Wed, Nov 16, 2016 at 11:10 AM, David Storrswrote: > Hi Meino, > > As a suggestions, you might want to read through this page on Stack > Overflow about how to ask technical questions: > http://stackoverflow.com/help/how-to-ask The summary is: tell us what > you're trying to achieve, what you've tried, and what *specifically* is not > working. > > The question you're asking here (about walk-lists) is hard to help with, > because it's not clear what the context is. I'll take my best shot, though: > > On Wed, Nov 16, 2016 at 10:04 AM, wrote: > >> Hi John, >> >> thank you for your reply ! :) >> >> ...no, not a homework... >> I want to teach myself some racket and hope 'to get it' finally... >> Since I am no native speaker I have the deficulty to search for >> things, which names I dont know... >> >> One example of my code is: >> >> (define (trim-list lst) >> (if (empty? lst) >> lst >> (cons (string-trim (car lst)) (trim-list (cdr lst) >> >> >> (define (walk-sublists lst) >> (if (empty? lst) >> lst >> (cons (trim-list (car lst)) (walk-sublists (cdr lst) >> >> I want to avoid to call trim-list, if 'car lst' returns an empty list. >> Instead 'car lst' sghould return the next non-empty list... >> >> I will take a look in the reference manual for 'filter' and 'compose'. >> >> Cheers >> Meino >> >> >> > You might try something like this: > > (define (trim-list lst) > (if (empty? lst) > lst > (cons (string-trim (car lst)) > (trim-list (cdr lst) > Dangit, GMail, hitting 'tab, space' does not necessarily mean I want to send, it might just mean I want to indent some code. Sorry for that, all. (define (trim-list lst) ...) ;; process a list, but skip any element of the list that is null (define (walk-sublists lst) (cond[(null? lst) null] [(null? (car lst)) (walk-lists (cdr lst))] [else (cons (trim-list (car lst)) (walk-sublists (cdr lst])) Code not tested, but let me know if it makes sense. Dave >> >> >> 'John Clements' via Racket Users >> [16-11-16 18:26]: >> > >> > > On Nov 15, 2016, at 19:52, meino.cra...@gmx.de wrote: >> > > >> > > Hi, >> > > >> > > I have a list of sublists. Some of the sublists are empty. >> > > The list should be processed recursevly and the resulting >> > > list should no longer contain empty sublists. >> > >> > Is this homework? >> > >> > if so: can you show your test cases? >> > >> > if not: (filter (compose not null?) l). >> > >> > >> > John Clements >> > >> > > >> > > The code I have so far looks like: >> > > >> > > (define (step-through-list lst) >> > >(if (empty? lst) >> > >lst >> > >(cons (process-sublist (car lst)) (step-through-list (cdr lst))) >> > > >> > > but "car" would feed empty sublists to process-sublist as any >> other >> > > sublist. How can I "silently" skip empty sublists and even get out of >> > > the recursion without harm (if the last sublist is empty) without >> > > switching to iteration? >> > > Is there something like "car-not-empty" ? ;) >> > > Or do I oversee the obvious here...? ;))) >> > > >> > > Thank you vary much for any help in advance! >> > > Cheers >> > > Meino >> > > >> > > >> > > -- >> > > You received this message because you are subscribed to the Google >> Groups "Racket Users" group. >> > > To unsubscribe from this group and stop receiving emails from it, >> send an email to racket-users+unsubscr...@googlegroups.com. >> > > For more options, visit https://groups.google.com/d/optout. >> > >> > >> > >> > -- >> > You received this message because you are subscribed to the Google >> Groups "Racket Users" group. >> > To unsubscribe from this group and stop receiving emails from it, send >> an email to racket-users+unsubscr...@googlegroups.com. >> > For more options, visit https://groups.google.com/d/optout. >> > >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to racket-users+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> > > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Recursevly processing a list with "wholes"
Hi Meino, As a suggestions, you might want to read through this page on Stack Overflow about how to ask technical questions: http://stackoverflow.com/help/how-to-ask The summary is: tell us what you're trying to achieve, what you've tried, and what *specifically* is not working. The question you're asking here (about walk-lists) is hard to help with, because it's not clear what the context is. I'll take my best shot, though: On Wed, Nov 16, 2016 at 10:04 AM,wrote: > Hi John, > > thank you for your reply ! :) > > ...no, not a homework... > I want to teach myself some racket and hope 'to get it' finally... > Since I am no native speaker I have the deficulty to search for > things, which names I dont know... > > One example of my code is: > > (define (trim-list lst) > (if (empty? lst) > lst > (cons (string-trim (car lst)) (trim-list (cdr lst) > > > (define (walk-sublists lst) > (if (empty? lst) > lst > (cons (trim-list (car lst)) (walk-sublists (cdr lst) > > I want to avoid to call trim-list, if 'car lst' returns an empty list. > Instead 'car lst' sghould return the next non-empty list... > > I will take a look in the reference manual for 'filter' and 'compose'. > > Cheers > Meino > > > You might try something like this: (define (trim-list lst) (if (empty? lst) lst (cons (string-trim (car lst)) (trim-list (cdr lst) > > > > > 'John Clements' via Racket Users > [16-11-16 18:26]: > > > > > On Nov 15, 2016, at 19:52, meino.cra...@gmx.de wrote: > > > > > > Hi, > > > > > > I have a list of sublists. Some of the sublists are empty. > > > The list should be processed recursevly and the resulting > > > list should no longer contain empty sublists. > > > > Is this homework? > > > > if so: can you show your test cases? > > > > if not: (filter (compose not null?) l). > > > > > > John Clements > > > > > > > > The code I have so far looks like: > > > > > > (define (step-through-list lst) > > >(if (empty? lst) > > >lst > > >(cons (process-sublist (car lst)) (step-through-list (cdr lst))) > > > > > > but "car" would feed empty sublists to process-sublist as any other > > > sublist. How can I "silently" skip empty sublists and even get out of > > > the recursion without harm (if the last sublist is empty) without > > > switching to iteration? > > > Is there something like "car-not-empty" ? ;) > > > Or do I oversee the obvious here...? ;))) > > > > > > Thank you vary much for any help in advance! > > > Cheers > > > Meino > > > > > > > > > -- > > > You received this message because you are subscribed to the Google > Groups "Racket Users" group. > > > To unsubscribe from this group and stop receiving emails from it, send > an email to racket-users+unsubscr...@googlegroups.com. > > > For more options, visit https://groups.google.com/d/optout. > > > > > > > > -- > > You received this message because you are subscribed to the Google > Groups "Racket Users" group. > > To unsubscribe from this group and stop receiving emails from it, send > an email to racket-users+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. > > > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Recursevly processing a list with "wholes"
> On Nov 16, 2016, at 1:04 PM, meino.cra...@gmx.de wrote: > > ...no, not a homework... > I want to teach myself some racket and hope 'to get it' finally... > Since I am no native speaker I have the deficulty to search for > things, which names I dont know... Meino, have you considered reading 'Die Macht der Abstraktion?’ (This is a guess based on your high-level domain.) — Matthias -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Recursevly processing a list with "wholes"
Hi John, thank you for your reply ! :) ...no, not a homework... I want to teach myself some racket and hope 'to get it' finally... Since I am no native speaker I have the deficulty to search for things, which names I dont know... One example of my code is: (define (trim-list lst) (if (empty? lst) lst (cons (string-trim (car lst)) (trim-list (cdr lst) (define (walk-sublists lst) (if (empty? lst) lst (cons (trim-list (car lst)) (walk-sublists (cdr lst) I want to avoid to call trim-list, if 'car lst' returns an empty list. Instead 'car lst' sghould return the next non-empty list... I will take a look in the reference manual for 'filter' and 'compose'. Cheers Meino 'John Clements' via Racket Users[16-11-16 18:26]: > > > On Nov 15, 2016, at 19:52, meino.cra...@gmx.de wrote: > > > > Hi, > > > > I have a list of sublists. Some of the sublists are empty. > > The list should be processed recursevly and the resulting > > list should no longer contain empty sublists. > > Is this homework? > > if so: can you show your test cases? > > if not: (filter (compose not null?) l). > > > John Clements > > > > > The code I have so far looks like: > > > > (define (step-through-list lst) > >(if (empty? lst) > >lst > >(cons (process-sublist (car lst)) (step-through-list (cdr lst))) > > > > but "car" would feed empty sublists to process-sublist as any other > > sublist. How can I "silently" skip empty sublists and even get out of > > the recursion without harm (if the last sublist is empty) without > > switching to iteration? > > Is there something like "car-not-empty" ? ;) > > Or do I oversee the obvious here...? ;))) > > > > Thank you vary much for any help in advance! > > Cheers > > Meino > > > > > > -- > > You received this message because you are subscribed to the Google Groups > > "Racket Users" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to racket-users+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. > > > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] a litle help
The program has a few errors. For example, * (define O ( X0 Y0 )) should be something like (define O (make-point X0 Y0)) (define O (point X0 Y0)) (define O (vector X0 Y0)) I'm not sure because the first two don't exist and I guess the last one is not what you want, but you must change that line to (define O (something X0 Y0)) * (* cos dT 30) I guess it should be (* (cos 30) dT) but you have to transform the 30 degrees to radians. -- My suggestion is to try first with an easier exercise. Try to draw a balloon that doesn't move. It's boring but the program is easier. Once you understand all the details about the framework to draw the non moving balloon, you can add the movement. Gustavo On Wed, Nov 16, 2016 at 6:54 AM, Masto Finewrote: > (define (ballon-tourne) > (local [(define LARG 110 ) > (define HAUT 110 ) > (define SCENE (carre 100 100 'outline "black")) > (define BALLON ( circle 5 'solid "red")) > (define X0 (/ LARG 2)) > (define Y0 (/ HAUT 2 )) > (define O ( X0 Y0 )) > (define M ( XM YM )) > (define P ((+ X0 30) Y0)) > (define t (angle OP OM )) > (define INIT 0) > (define dT 5) > (define (suivant t) > ((+ X0 (* cos dT 30)( - Y0 (* sin dT ) > (define (dessiner t) > (place-image BALLON ( (+ X0 ( * cos t 30))(- Y0 (*sin t) > (define (final? t) >(= t 700))] > (big-bang INIT > (on-tick suivant) > (on-draw dessiner) > (stop-when final?can you correct me : > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[racket-users] a litle help
(define (ballon-tourne) (local [(define LARG 110 ) (define HAUT 110 ) (define SCENE (carre 100 100 'outline "black")) (define BALLON ( circle 5 'solid "red")) (define X0 (/ LARG 2)) (define Y0 (/ HAUT 2 )) (define O ( X0 Y0 )) (define M ( XM YM )) (define P ((+ X0 30) Y0)) (define t (angle OP OM )) (define INIT 0) (define dT 5) (define (suivant t) ((+ X0 (* cos dT 30)( - Y0 (* sin dT ) (define (dessiner t) (place-image BALLON ( (+ X0 ( * cos t 30))(- Y0 (*sin t) (define (final? t) (= t 700))] (big-bang INIT (on-tick suivant) (on-draw dessiner) (stop-when final?can you correct me : -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.