Hi all,
...think, I have to apologize....
I screwed it up....it is a language (spoke one...not "programming" )
thing:
I read "List of strings" which in german is "Liste von Zeichenketten".
THIS expression means this:
"A" "B" "C"
(for example).
This applied to string-join in a germenglish head forms:
(string-join "A" "B" "C" "seperator")
But I had
(define lst (list "A" "B" "C"))
(string-join lst "seperator")
...so I thougt I need an "apply" to move the
string-join right in front of the "list of strings" (spoken language)
in the list of strings (racket-speak).
But despite of the nonsense I thought I now have learned
how to handle functions with additional arguments in case
of the need to 'apply' them.
Thanks a lot Shu-Hung, for you help and the patience of all
who wanted de-confuse me ;)
(THANKS!)
Cheers,
Meino
Shu-Hung You <shh...@u.northwestern.edu> [16-10-29 18:08]:
> Hi Meino,
>
> Could you give an example of lst or line? Unlike string-append, most of the
> time
> string-join doesn't really require an 'apply'. As we can see:
>
> > (string-append "a" "b" "c")
> "abc"
> > (string-join '("a" "b" "c") ":")
> "a:b:c"
>
> While string-append takes all its arguments and concatenates them into a
> string,
> string-join simply joins all the strings in its first argument (which
> should be a list of strings).
> So suppose we have 'line' to be a list of string, then string-append
> and string-join can
> be used as follows:
>
> > (define line '("x" "y" "z"))
> > (apply string-append line)
> "xyz"
> > (string-join line " ")
> "x y z"
>
> If string-join is really to be used with apply, then we need to first
> construct its arguments
> into a list. For instance, the first of example of string-join is turned into:
>
> > (string-join '("a" "b" "c") ":")
> "a:b:c"
> > (apply string-join '(("a" "b" "c") ":"))
> "a:b:c"
>
> Given 'line' to be a list of strings, we need to construct the
> separator as the second item in
> the argument list of string-join:
>
> > (define line '("x" "y" "z"))
> > (apply string-join (list line " "))
> "x y z"
>
> Best,
> Shu-Hung
>
> On Sat, Oct 29, 2016 at 10:31 AM, <meino.cra...@gmx.de> wrote:
> >
> > Hi Stephen,
> >
> > thanks for yoru reply ! ::)
> >
> > At the certain point of the program I get
> > a list as parameter 'lst', which contains
> > the sublists of strings. I wrote this
> > function:
> >
> >
> > (define (to-txt lst)
> > (if (empty? lst)
> > lst
> > (let ((line (car lst)))
> > (begin
> > (displayln (apply string-join line " " )) ;;; WRONG SYNTAX HERE
> > (to-txt (cdr lst))))))
> >
> > Since I get the sublists as parameters I need an 'apply' to 'inject'
> > (sorry...I am no native speaker...) 'string-join' into the list.
> >
> > But string-join has additional parameters, and I dont know how to
> > combine those with 'apply'?
> >
> > PS: The resulting strings will later be processed further... the
> > 'displayln' is just a placeholder...
> >
> > Cheers,
> > Meino
> >
> >
> > Stephen Chang <stch...@ccs.neu.edu> [16-10-29 17:16]:
> >> string-join already expects a list of strings, so are you sure you want
> >> apply?
> >> Can you give a more specific example?
> >>
> >> Perhaps map or some other iteration is what you want?
> >>
> >> (for ([strs '(("a" "b") ("c" "D" "E"))])
> >> (displayln (string-join strs " ")))
> >>
> >> =>
> >> a b
> >> c D E
> >>
> >> On Sat, Oct 29, 2016 at 10:27 AM, <meino.cra...@gmx.de> wrote:
> >> > Hi,
> >> >
> >> > ...still improving my shortwave-broadcaster-dumper... :)
> >> >
> >> > I have a list with sublists of strings, which I want to concatenate.
> >> > Each sublist shall form one line of output.
> >> > I tried 'string-append', but this gives me something like this
> >> > (excerpt):
> >> > "189RikisutvarpidRas1+20000-24001234567Icelandic"
> >> > ...the separating #\space is missing.
> >> >
> >> > The according code looks like this (excerpt)
> >> >
> >> > (apply string-append sublist)
> >> >
> >> > then I found 'string-join' which has extra-parameters
> >> > to define separator of all kinds.
> >> >
> >> > ...but...how can I express the 'apply'-instruction...with the
> >> > addional parameters???
> >> >
> >> > This looks something inbetween funny and weird:
> >> >
> >> > (apply string-join sublist " ")
> >> >
> >> > and racket mumbles:
> >> > apply: contract violation
> >> > expected: list?
> >> > given: " "
> >> > argument position: 3rd
> >> > other arguments...:
> >> > #<procedure:string-join>
> >> >
> >> >
> >> > ?
> >> >
> >> > Cheers
> >> > Meino
> >> >
> >> >
> >> >
> >> >
> >> >
> >> > --
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