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Re: Lost in Loop

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B. Pym wrote:

> Pascal Bourguignon wrote:
> 
> > > it to learn Lisp.  Basically, for a list of book titles I wanted to
> > > return a list of position in text and the book title, so
> > > (build-book-index "wjhedbwjhbMarkajbdadbGenesis" books)
> > > 
> > > gave: ((21 "Genesis") (10 "Mark")).
> > > 
> > > I had an approach working but it looked horrid so I thought I would try
> > > loop.  I came up with this:
> > > 
> > > (defun build-book-index (text books)
> > >  (loop for book in books
> > >     when (search (string-downcase book) (string-downcase text)) collect
> > >     (list it book)))
> > > 
> > > Of course, ...collect it ... worked but the version above gave:
> > > 
> > > in: LAMBDA NIL
> > > ;     (LIST IT BOOK)
> > > ; caught WARNING:  undefined variable: IT
> > > 
> > > Is this expected?
> > 
> > Yes.
> > 
> > > How can I get round it?
> > 
> > Not using IT.
> > 
> > (defun build-book-index (text books)
> >   (loop
> >      for book in books
> >      for my-it = (search (string-downcase book) (string-downcase text))
> >      when my-it collect (list my-it book)))
> 
> Gauche Scheme
> 
> (use srfi-13)  ;; string-contains-ci
> 
> (define (build-book-index text books)
>   (filter-map~ book
>     (let1 p (string-contains-ci text book)
>       (and p (list p book)))
>     books))
> 
> (build-book-index "foo.tiger lillies.bar.dead calm.what"
>   '("whammo" "Tiger Lillies" "Dead Calm"))
> 
>   ===>
> ((4 "Tiger Lillies") (22 "Dead Calm"))
> 
> Given:
> 
> (define-syntax fn*
>   (syntax-rules ()
>     [(_ (a b c ... . d) . z)
>      (lambda (xs)
>        (let-values (((a b c ... . d) (apply valuevs xs))) . z))]
>     [(_ (v ...) . z)
>      (lambda (xs) (let-values (((v ...) (apply values xs))) . z))]
>     [(_ (a . b) . z)
>      (lambda (xs) (let ((a (car xs)) (b (cdr xs))) . z)) ]
>     [(_ a . z) (lambda (a) . z) ] ))
> 
> (define-syntax filter-map~
>   (syntax-rules ()
>     [(_ (v0 v1 ...) expr seq0 seq1 seq2 ...)
>      (filter-map (lambda(v0 v1 ...) expr) seq0 seq1 seq2 ...) ]
>     [(_ v expr seq) (filter-map (fn* v expr) seq) ] ))

Using an anaphoric macro:

(define (build-book-index text books)
  (keep book (string-contains-ci text book) (list it book)
    books))

Given:


(define-macro keep
  (case-lambda
    ((pred seq)  `(filter ,pred ,seq))
    ((v test expr seq)
     `(filter-map
        (lambda(,v) (let ((it ,test)) (and it ,expr)))
        ,seq))
    ((v test seq)
     `(filter (lambda(,v) ,test) ,seq))))

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Re: Lost in Loop "B. Pym" <Nobody447095@here-nor-there.org> - 2025-08-15 07:22 +0000
  Re: Lost in Loop "B. Pym" <Nobody447095@here-nor-there.org> - 2025-08-15 08:03 +0000

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