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
(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] | [#x10000-#x10FFFF]), 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.
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