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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