Re: [Chicken-users] html-stream: idiom for large iterations?

[Alejandro Forero Cuervo]

Hey.

> I'm fairly new to Scheme and streams, and am trying to grok how to use
> the html-stream extension to generate an HTML document with a large
> repeating section. I wrote the following (to compare its performance
> to similar functions I implemented other languages):
> 
> (require-extension html-stream)
> (stream->string
>  (html-stream
>   (html (head (title "Hello, world!"))
>    (body (ul
>           (apply stream-append
>                  (map (lambda (x) (html-stream
>                                    (li "This is item " x)))
>                       (iota 1000))))))))
> 
> However, this fails because the (map) generates a list of 1000
> elements, which exceeds the parameter limit for (apply).
> 
> Is there an idiomatic way to rewrite this, and avoid the parameter limit?

I would suggest using “stream-concatenate” instead of “apply
stream-append” (or even “fold-right stream-append”).  The only
difference is that you wouldn't pass a list but a stream.  This has
one advantage (that is usually minor but can, in some cases, make a
very big difference): the information you are appending
(concatenating) is only built as it is consumed.

Your code would thus look like this:

  (require-extension html-stream stream-ext)
  (stream->string
   (html-stream
    (html (head (title "Hello, world!"))
     (body
      (ul
       (stream-concatenate
        (stream-map (lambda (x) (html-stream (li "This is item " x)))
                    (stream-iota 1000))))))))

stream-concatenate is defined in the stream-ext egg; since you are
doing stream-append, I suppose you're already using it.

I hope it works.

Alejo.
http://bachue.com/alejo

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