HTML Page

By means of the library(spin) we wrote a HTTP server that does serve two pages /style.css and /moon.cgi. The style sheet /style.css is a static file served from the file system, it is used to give the SVG elements some styling such as a fill colour:

dispatch('/style.css', _, _, Res) :-
   http_write_head(Res, 200,
        ['content-type'-'text/css; charset=utf-8']),
   http_text_new(Res, S),
   open('style.css', read, T),
   Etc..

The dynamic page /moon.cgi will present the description and present the sunlit portion in a page with forward and backward links. If the day is not given in the URL query parameters it will take the current day:

dispatch('/moon.cgi', List, _, Res) :-
   http_write_head(Res, 200,
       ['content-type'-'text/html; charset=utf-8']),
   http_text_new(Res, S),
   dom_output_new(S, T),
   (member(day - Day2, List) ->
      sys_time_atom('%Y-%m-%d', Time, Day2);
      statistics(wall, Time)),
   phase(Time, Phase),
Etc..

The learning curve is not extremely high, since there is no need to generate a Prolog term, that would describe the output. The developer can freely interleave output statements and computation statements. As he is most likely already used when dealing with a TTY.

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