char-numeric? and digits

[soegaard]

The documentation [1] suggests that char-numeric? is only true for digits:

However, it returns true for unicode symbols that have the numeric property.

That behaviour matches R6RS, so I think the docs needs a little touch up.

However, it might be an idea to add a char-digit?.

[1] https://scheme.com/tspl4/objects.html#./objects:s203

[soegaard]

A list of unicode characters with the numeric property.

https://www.johndcook.com/unicode_numbers.html

[soegaard]

Note that R7RS has introduced digit-value to convert a unicode character with the numeric property to a an integer value (as counted from the nearest "zero").

https://small.r7rs.org/ticket/220/

Example from Gambit:

> (digit-value #\u0665)
5
> #\u0665 
#\٥

The odd looking character is an "Arabic-Indic Digit Five".