Hi Andreas, a good explanation is here: https://stackoverflow.com/questions/31909121/how-does-the-named-let-in-the-form-of-a-loop-work personally i avoid to use it, as i can do the same with internal definitions . regards, Damien
On Sat, Feb 3, 2024 at 10:49 PM Andreas Reuleaux <r...@a-rx.info> wrote: > Hi, > > I have a hard time understanding the let binding lp ... > in the function element->xml - from module sxml simple - > repeated here for convenience. > > > --8<---------------cut here---------------start------------->8--- > (define (element->xml tag attrs body port) > (check-name tag) > (display #\< port) > (display tag port) > (if attrs > (let lp ((attrs attrs)) > (if (pair? attrs) > (let ((attr (car attrs))) > (display #\space port) > (if (pair? attr) > (attribute->xml (car attr) (cdr attr) port) > (error "bad attribute" tag attr)) > (lp (cdr attrs))) > (if (not (null? attrs)) > (error "bad attributes" tag attrs))))) > (if (pair? body) > (begin > (display #\> port) > (let lp ((body body)) > (cond > ((pair? body) > (sxml->xml (car body) port) > (lp (cdr body))) > ((null? body) > (display "</" port) > (display tag port) > (display ">" port)) > (else > (error "bad element body" tag body))))) > (display " />" port))) > --8<---------------cut here---------------end--------------->8--- > > Some background: sxml simple is - as the name implies - > simple (or should be so). - It's implements > > * functions for parsing xml to s-expression > xml->sxml, ... > > * and functions for serializing sxml to xml > sxml->xml, ... (and among them: element->xml, as above) > > This second task (group of functions) is even simpler > (than the parsing stuff) - I would say. > > Now these function (sxml->xml, element->xml) work for > me: I can test them with some simple s-expression foo for example > > --8<---------------cut here---------------start------------->8--- > (define foo > '(d:para (d:emphasis (@ (role "strong")) "system analyst") " for " > (d:link (@ (xl:href "http://www.blah.com";)) (d:emphasis (@ (role > "strong")) "Blah")) " in Berlin, and so on")) > --8<---------------cut here---------------end--------------->8--- > > > --8<---------------cut here---------------start------------->8--- > scheme@(guile-user) [13]> (sxml->xml foo) > <d:para><d:emphasis role="strong">system analyst</d:emphasis> for > <d:link xl:href="http://www.blah.com";><d:emphasis > role="strong">Blah</d:emphasis></d:link> in Berlin, and so on</d:para> > --8<---------------cut here---------------end--------------->8--- > > > sxml->xml making use of element->xml above. > Now with regards to the binding / usage of lp above: it is > bound / used several times: > > > (let lp ((attrs attrs)) ... > let lp be a function that ... does what? > > > (lp (cdr attrs))) > now call this function with (cdr attrs). > What does it do? > set attrs to (cdr attrs)? > > > then similar below > (let lp ((body body)) ... > ??? > > > (lp (cdr body))) > ??? > > > For one thing I am used to > > (let bindings body) > > with bindings being of the form > ((x 'foo) > (y 'bar)) > > (i.e. bind x with 'foo, y with 'bar when executing body) > > for example, lp is not of this style. Maybe if there is just one variable > bound > one can shortcut this to > > let x 'foo body > > Is this what's going on above? And if so: > then lp is bound to a list of one pair? : > > ((attrs attrs)) > > how come can we call this as a function then later. > > And if attrs is a function (which I doubt) that what > is the application of attrs to attrs? > > Anyway: confused. - Thanks in advanc, > A' > > > > > > > > > > > > > > >
