Hi Alexander, I asked this question some time ago: http://article.gmane.org/gmane.comp.lang.racket.user/3420/match=structure+question
I got a very good answer from Matthias Felleisen who showed how this could be achieved: http://article.gmane.org/gmane.comp.lang.racket.user/3437/match=structure+question Hope this helps in some way. -- Manfred On Fri, 6 Jun 2014 16:59:41 -0400 "Alexander D. Knauth" <alexan...@knauth.org> wrote: > Is there a way to define a type constructor that accepts keyword > arguments? > > I know that things like the Class type constructor do this already, > so is there a way to define something like this myself? > > The reason is I have a struct that represents a dimension (as in > dimensional analysis and units) and I want a type constructor that > lets me make types for specific instances of it without having to > remember what order the fields go in: > > (struct: (Length-Expt Mass-Expt Time-Expt Charge-Expt Temp-Expt) > dimension > ([length-expt : Length-Expt] > [mass-expt : Mass-Expt] > [time-expt : Time-Expt] > [charge-expt : Charge-Expt] > [temperature-expt : Temp-Expt]) > ) > > (define (dimension--kws #:length^ [length-expt 0] > #:mass^ [mass-expt 0] > #:time^ [time-expt 0] > #:charge^ [charge-expt 0] > #:temperature^ [temp-expt 0]) > (dimension length-expt mass-expt time-expt charge-expt temp-expt)) > > ;; I want to be able to do something that would do the same thing as > this: (it doesn't have to be this easy) (define-type (Dimmension--kws > #:length^ Length-Expt #:mass^ Mass-Expt > #:time^ Time-Expt > #:charge^ Charge-Expt > #:temperature^ Temp-Expt) > (dimension Length-Expt Mass-Expt Time-Expt Charge-Expt Temp-Expt)) > > > ____________________ Racket Users list: http://lists.racket-lang.org/users
