Re: [racket-users] Why does 1 count as numeric in xexpr, but 0 does not?

2017-03-14 Thread Marc Kaufmann 
Fair enough if that's the specification, even if it is unexpected (to me at 
least). Thanks,

Marc

On Tuesday, March 14, 2017 at 10:41:02 AM UTC-4, Jay McCarthy wrote:
> Hi Marc,
> 
> libxml2 only allows numeric entity references in this range:
> 
> * [2] Char ::= #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD]
> * | [#x1-#x10]
> 
> Racket doesn't fully respect that, but both disallow 0. I think we
> should match libxml2 and tighten the contract.
> 
> Jay
> 
> -- 
> -=[ Jay McCarthy   http://jeapostrophe.github.io]=-
> -=[ Associate ProfessorPLT @ CS @ UMass Lowell ]=-
> -=[ Moses 1:33: And worlds without number have I created; ]=-

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Re: [racket-users] Why does 1 count as numeric in xexpr, but 0 does not?

2017-03-14 Thread Jay McCarthy 
Hi Marc,

libxml2 only allows numeric entity references in this range:

* [2] Char ::= #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD]
* | [#x1-#x10]

Racket doesn't fully respect that, but both disallow 0. I think we
should match libxml2 and tighten the contract.

Jay

-- 
-=[ Jay McCarthy   http://jeapostrophe.github.io]=-
-=[ Associate ProfessorPLT @ CS @ UMass Lowell ]=-
-=[ Moses 1:33: And worlds without number have I created; ]=-

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Re: [racket-users] Why does 1 count as numeric in xexpr, but 0 does not?

2017-03-14 Thread Marc Kaufmann 
I understand that the number 1 is different from the string (although I would 
probably have expected it to be turned into a string before being passed to the 
browser or something, but it doesn't matter for my purposes). What does 
surprise me is that (xexpr->string 1) gives , yet (xexpr->string 0) does not 
give  but throws an error. Is this due to the XML specification, or due to 
the Racket implementation of X-expressions?

Cheers,
Marc



On Monday, March 13, 2017 at 10:32:50 PM UTC-4, Philip McGrath wrote:
> Numbers in x-expressions are interpreted as XML entities, not as the string 
> representation of the number. The value of (xexpr->string '(html 1)), to use 
> your example, is "". The 1 represents the character that 
> Racket would represent as #\u0001, i.e. the value of (integer->char 1). In 
> contrast, (char->integer #\1) produces 49.
> 
> 
> 
> -Philip
> 
> 
> 
> On Mon, Mar 13, 2017 at 8:38 PM, Marc Kaufmann  wrote:
> Hi,
> 
> 
> 
> I am creating matrices of 0s and 1s that I display in HTML-tables and 
> somewhat surprisingly I found out that 0s are not permissible in 
> X-expressions, while 1s are:
> 
> 
> 
> (require web-server/http)
> 
> 
> 
> (response/xexpr '(html 1)) ; Fine, no trouble.
> 
> (response/xexpr '(html 0)) ; Blow-up.
> 
> 
> 
> The specific violation is the following:
> 
> 
> 
> "response/xexpr: contract violation;
> 
>  Not an Xexpr. Expected a string, symbol, valid numeric entity, comment, 
> processing instruction, or list, given 0"
> 
> 
> 
> After some digging around, it turns out that only numbers that satisfy 
> valid-char? are acceptable, which means "exact-nonnegative-integer whose 
> character interpretation under UTF-8 is from the set ([#x1-#xD7FF] | 
> [#xE000-#xFFFD] | [#x1-#x10]), in accordance with section 2.2 of the 
> XML 1.1 spec."
> 
> 
> 
> First, should 0 really not be accepted? (I am not going to try and figure out 
> the UTF-8 interpretation...) And second, is the reason that negative numbers 
> are not acceptable that they are not under the XML spec above? This took me 
> by surprise and means I have to put number->string in a bunch of places.
> 
> 
> 
> Cheers,
> 
> Marc
> 
> 
> 
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Re: [racket-users] Why does 1 count as numeric in xexpr, but 0 does not?

2017-03-13 Thread Philip McGrath 
Numbers in x-expressions are interpreted as XML entities, not as the string
representation of the number. The value of (xexpr->string '(html 1)), to
use your example, is "". The 1 represents the character
that Racket would represent as #\u0001, i.e. the value of (integer->char
1). In contrast, (char->integer #\1) produces 49.

-Philip

On Mon, Mar 13, 2017 at 8:38 PM, Marc Kaufmann 
wrote:

> Hi,
>
> I am creating matrices of 0s and 1s that I display in HTML-tables and
> somewhat surprisingly I found out that 0s are not permissible in
> X-expressions, while 1s are:
>
> (require web-server/http)
>
> (response/xexpr '(html 1)) ; Fine, no trouble.
> (response/xexpr '(html 0)) ; Blow-up.
>
> The specific violation is the following:
>
> "response/xexpr: contract violation;
>  Not an Xexpr. Expected a string, symbol, valid numeric entity, comment,
> processing instruction, or list, given 0"
>
> After some digging around, it turns out that only numbers that satisfy
> valid-char? are acceptable, which means "exact-nonnegative-integer whose
> character interpretation under UTF-8 is from the set ([#x1-#xD7FF] |
> [#xE000-#xFFFD] | [#x1-#x10]), in accordance with section 2.2 of
> the XML 1.1 spec."
>
> First, should 0 really not be accepted? (I am not going to try and figure
> out the UTF-8 interpretation...) And second, is the reason that negative
> numbers are not acceptable that they are not under the XML spec above? This
> took me by surprise and means I have to put number->string in a bunch of
> places.
>
> Cheers,
> Marc
>
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[racket-users] Why does 1 count as numeric in xexpr, but 0 does not?

2017-03-13 Thread Marc Kaufmann 
Hi,

I am creating matrices of 0s and 1s that I display in HTML-tables and somewhat 
surprisingly I found out that 0s are not permissible in X-expressions, while 1s 
are:

(require web-server/http)

(response/xexpr '(html 1)) ; Fine, no trouble.
(response/xexpr '(html 0)) ; Blow-up.

The specific violation is the following:

"response/xexpr: contract violation;
 Not an Xexpr. Expected a string, symbol, valid numeric entity, comment, 
processing instruction, or list, given 0"

After some digging around, it turns out that only numbers that satisfy 
valid-char? are acceptable, which means "exact-nonnegative-integer whose 
character interpretation under UTF-8 is from the set ([#x1-#xD7FF] | 
[#xE000-#xFFFD] | [#x1-#x10]), in accordance with section 2.2 of the 
XML 1.1 spec." 

First, should 0 really not be accepted? (I am not going to try and figure out 
the UTF-8 interpretation...) And second, is the reason that negative numbers 
are not acceptable that they are not under the XML spec above? This took me by 
surprise and means I have to put number->string in a bunch of places.

Cheers,
Marc

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