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destructive append to a string
Posted: Sat Dec 17, 2005 2:16 pm
by Dmi
Is there a way to destructive append to the end of string?
Similar to 'push?
Posted: Sat Dec 17, 2005 2:23 pm
by HPW
Use:
From the help-file:
Code: Select all
;; fast in-place string appending
(set 'str "")
(dotimes (x 5) (write-buffer str "hello"))
Posted: Sat Dec 17, 2005 2:32 pm
by Dmi
Oh! Thanks!
Posted: Sat Dec 17, 2005 4:17 pm
by Lutz
... and 'write-line' works too for destructive string append.
About your XML questions/example. I don't see a streight forward way to do it, but you might look into 'implicit indexing' as a short way of writing/accessing elements or sublists from a deeply complex nested list structure like returned from 'xml-parse':
Code: Select all
(xml-type-tags nil nil nil nil)
(set 'page (xml-parse (read-file "myfile.xml") (+ 1 4 8 16)))
(set 'sheet-type (page 0 2 4 1 0))
You may also want to look into 'ref' as a means to get the right indices of an element or sublist in the nested list returned:
Code: Select all
> (set 'L '(foo bar (sheet-name "my Sheet")))
(foo bar (sheet-name "my Sheet"))
> (ref 'sheet-name L)
(2 0)
> (L ((ref 'sheet-name L) 1))
foo
> (L ((ref 'sheet-name L) 0))
(sheet-name "my Sheet")
> ((L ((ref 'sheet-name L) 0)) 1)
"my Sheet"
>
This combines 'ref' and implicit indexing. Of course you could also use 'nth', 'first', 'last' etc., but it is more to write (and sometimes more readable too).
Lutz
Posted: Sat Dec 17, 2005 4:36 pm
by Lutz
.. and her is another trick:
Code: Select all
;; you somehow extracted from a complex XML structure:
> sheet-spec
(sheet-name "MySheet")
;; define a procedure for this an other tags
> (define (sheet-name s) (append "the sheet-name is: " s))
;; then evaluate the list structure
> (eval sheet-spec)
"the sheet-name is: MySheet"
This technique could also be used to generate XML/HTML from a list stucture.
Lutz
Posted: Sat Dec 17, 2005 4:40 pm
by Dmi
Hmm... nice trick! I sould to think around it...
Thanks!