p.s. > Also: Am I correct that the user-supplied function gets JIT-ed, and > there's no big performance hit from this? (I think the answer is no,
That question had mixed polarities. :) I should have written, I think the answer is No there's no big performance hit, and Yes it gets JIT-ed. On Thu, May 23, 2013 at 2:22 PM, Greg Hendershott <[email protected]> wrote: > I've never had a reason to use `dynamic-require`, but now I think I do. > > For my Frog static blog generator, I'd like to provide a light > "template" feature, where the user can override the default layout of > the main container <div> in the page. > > I have an existing function that returns an xexpr for this. So my idea > is to let the user optionally supply a `template.rkt` file that > `provide`s a function named (say) `container` that returns (listof > xexpr?). > > So I think what I want to do is something like this: > > (define (container-proc) > (define p (build-path (src-path) "template.rkt")) > (cond [(file-exists? p) > (dynamic-require p > 'container > (thunk default-container))] > [else default-container])) > > The built-in `default-container` looks something like this: > > (define (default-container bootstrap-row-class ;"row" or "row-fluid" > bodies ;listof xexpr?: main content > tocs ;listof xexpr?: TOC > tags/feeds ;listof xexpr?: tag/feed links > follow) ;listof xexpr?: Twitter, etc. > `((div ([class ,bootstrap-row-class]) > ;; Left column > (div ([id "left-sidebar"] > [class "span2 bs-docs-sidebar"]) > ,@tocs > (p nbsp)) > ;; Main column > (div ([id "content"] > [class "span8"]) > ,@bodies) > ;; Right column > (div ([id "right-sidebar"] > [class "span2"]) > ,@(tags/feeds) > ,@(follow))))) > > The user-supplied template.rkt would provide some variation on it. For > example they don't want any left column with a TOC, so they supply > this: > > ;; template.rkt > #lang racket > (provide container) > (define (container bootstrap-row-class ;"row" or "row-fluid" > bodies ;listof xexpr?: main content > tocs ;listof xexpr?: TOC > tags/feeds ;listof xexpr?: tag/feed links > follow) ;listof xexpr?: Twitter, etc. > `((div ([class ,bootstrap-row-class]) > ;; Don't want any left column; ignore `tocs` > ;; Main column > (div ([id "content"] > [class "span9"]) ;wider > ,@bodies) > ;; Right column: Tags/feeds/follow > (div ([id "right-sidebar"] > [class "span3"]) ;wider > ,@(tags/feeds) > ,@(follow))))) > > In a quick experiment this seems to work fine. I could also go further > and make this a tiny s-exp #lang, to make the end user experience even > simpler. But meanwhile, and before that, I just want to make sure that > `dynamic-require` is a reasonable way to do this? Does anyone > disagree? > > Also: Am I correct that the user-supplied function gets JIT-ed, and > there's no big performance hit from this? (I think the answer is no, > because from reviewing Racket's own source, I got the impression that > all modules are built on dynamic-require, but I might have > understood.) > > Thank you in advance for any advice or suggestions! ____________________ Racket Users list: http://lists.racket-lang.org/users
