Re: How to recover whitespace from syntax->string

It turns out that I have more trouble with printing whitespace from 
syntax.  Consider this:

    (require racket)
    (require syntax/to-string)

    (define (syntax-on-lines-v1 xs)
       (define (iter fin ys)
         (let ((y (read-syntax "<string>" fin)))
           (if (eof-object? y)
               (reverse ys)
               (iter fin (cons y ys)))))
       (if (null? xs)
           '()
           (let* ((fout (open-output-string))
                  (_ (for* ((x xs))
                       (writeln x fout)))
                  (_ (close-output-port fout))
                  (fin (open-input-string (get-output-string fout))))
             (port-count-lines! fin)
             (iter fin '()))))

The basic case works:

    ;; ex1
    (let* ((xs '("collected" "from" "separate" "lines"))
            (ys (syntax-on-lines xs)))
       (syntax->string
        #`(#,@ys)))
    ;; "\"collected\"\n\"from\"\n\"separate\"\n\"lines\""

But I need to decorate a number of constant items, such as:

    ;; ex2
    (let* ((xs '("collected" "from" "separate" "lines"))
            (ys (syntax-on-lines xs)))
       (syntax->string
        #`(comment #,@ys)))
    ;; "comment\"collected\"\"from\"\"separate\"\"lines\""

In ex2, the loss of line breaks seems to stem from lack of srcloc info 
on the first token.  However, I don't understand just what's necessary 
to keep things moving along.  If I populate the first token only with 
quasisyntax/loc as follows, I get my EOLs:

    ;; ex3
    (let* ((xs '("collected" "from" "separate" "lines"))
            (ys (syntax-on-lines xs))
            (zs (cons (quasisyntax/loc (car ys) "comments") ys)))
       (syntax->string
        #`(#,@zs)))
    ;; "\"comments\"\"collected\"\n\"from\"\n\"separate\"\n\"lines\""

But that's quite inconvenient if I have a bunch of stuff to decorate.  
If I try to do the more convenient outside position for quasisyntax/loc, 
my EOL data seems to get overwritten:

    ;; ex4
    (let* ((xs '("collected" "from" "separate" "lines"))
            (ys (syntax-on-lines xs)))
       (syntax->string (quasisyntax/loc (car ys) ("comments" #,@ys))))
    ;; "\"comments\"\"collected\"\"from\"\"separate\"\"lines\""

Is there a way to do something like ex4, where I can add a number of new 
constant tokens, but without overwriting the EOL data?

Thanks in advance,


Jeff Henrikson


On 4/9/21 9:57 AM, Jeff Henrikson wrote:
>
> Laurent,
>
> Thank you very much.  It probably would have taken me a long time on 
> my own to think of the possibility that the port was at fault.
>
>
> Jeff
>
>
> On 4/9/21 4:29 AM, Laurent wrote:
>> You need to enable line/character counting with `port-count-lines!`:
>>
>> #lang racket
>> (require syntax/to-string)
>>
>> (define in (open-input-string "(comment\n  \"hello world\"\n  line)"))
>> (port-count-lines! in)
>> (syntax->string (read-syntax "mystring" in))
>>
>> ; -> "comment\n \"hello world\"\n line"
>>
>> On Fri, Apr 9, 2021 at 2:10 AM Jeff Henrikson <[email protected] 
>> <mailto:[email protected]>> wrote:
>>
>>     Racket users,
>>
>>     I’m trying to read a scheme file, decorate a bit of window
>>     dressing around the edges, and write the expressions to a new
>>     file.  I’ve got the basic mechanism working with (read . . .) and
>>     (pretty-write . . .), but of course that doesn’t preserve
>>     linebreaks.  So now I’m trying to improve it to preserve
>>     linebreaks.  It would be nice to preserve all whitespace, but
>>     I'll settle for linebreaks.  The racket docs seem to suggest it
>>     is possible:
>>
>>         2.6 Rendering Syntax Objects with Formatting
>>          (require syntax/to-string)     package: base
>>                 procedure
>>                 (syntax->string stx-list) → string?
>>               stx-list : (and/c syntax? stx-list?)
>>         Builds a string with newlines and indenting according to the
>>         source locations in stx-list; the outer pair of parens are
>>         not rendered from stx-list.
>>
>>     However, when I evaluate:
>>
>>         (syntax->string (read-syntax "mystring" (open-input-string
>>         "(comment\n  \"hello world\"\n line)")))
>>
>>     I get:
>>
>>         "comment\"hello world\"line"
>>
>>     which has no whitespace at all, not even the whitespace that is
>>     necessary to separate the original tokens.
>>
>>     I get a similar behavior if I read-syntax from a file and apply
>>     syntax->string to those values.
>>
>>     Does anyone know how to get syntax->string to recover the
>>     original whitespace?
>>
>>     I'm using Racket 8.0 cs on Ubuntu 20.
>>
>>
>>     Thanks in advance,
>>
>>
>>     Jeff Henrikson
>>
>>
>>     -- 
>>     You received this message because you are subscribed to the
>>     Google Groups "Racket Users" group.
>>     To unsubscribe from this group and stop receiving emails from it,
>>     send an email to racket-users+unsubscribe-/[email protected]
>>     <mailto:racket-users+unsubscribe-/[email protected]>.
>>     To view this discussion on the web visit
>>     https://groups.google.com/d/msgid/racket-users/95dd99f5-2d04-a607-ed11-bc235095eeb7%40gmail.com
>>     <https://groups.google.com/d/msgid/racket-users/95dd99f5-2d04-a607-ed11-bc235095eeb7%40gmail.com?utm_medium=email&utm_source=footer>.
>>

-- 
You received this message because you are subscribed to the Google Groups "Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/[email protected]
To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/5c23d277-8508-3fce-d925-e45cfb6e5452%40gmail.com.