I found a book on programming language design which you can download from
here:
  http://cseng.aw.com/book/related/0,3833,0805311912+20,00.html#top

It contains two ideas which I found particularly intriguing, although I don't know whether they would be worth adding to a language, overall.


"Power Loops" are a cross between "for" loops and recursive functions. E.g., use "nest" to say "this for loop can be at different levels" and "deeper" to go to the next level:

   variable
      Queen : array 1 ..n of integer;

   nest Column := 1 to n
      for Queen[Column] := 1 to n do
         if OkSoFar(Column) then
            deeper;
         end; -- if OkSoFar(Column)
      end; -- for Queen[Column]
   do
      write(Queen[1..n]);
   end;

Of course, they would only rarely be useful.


You can also use dimensions as a kind of meta-type to help type-safety and make sure that you don't make bad conversions.  E.g.:

   dimension
      area = distance * distance;
      velocity = distance / time;
   constant
      mile = 5280 * foot;  -- foot is predeclared
      acre = mile * mile / 640;
   variable
      d1, d2 : distance real;
      a1 : area real;
      v1 : velocity real;
   (etc.)

This might be useful in science and engineering.  In D it could be achieved using (string) typedefs and conversion macros so I don't imagine it would be worth adding.


What do you think about these?

Dimensional programming probably would be interesting for science and engineering apps. -Walter

"Ben Cohen" <bc@skygate.co.uk> wrote in message news:9secuk$2oja$1@digitaldaemon.com...
> I found a book on programming language design which you can download from
> here:
>   http://cseng.aw.com/book/related/0,3833,0805311912+20,00.html#top
>
> It contains two ideas which I found particularly intriguing, although I don't know whether they would be worth adding to a language, overall.
>
>
> "Power Loops" are a cross between "for" loops and recursive functions. E.g., use "nest" to say "this for loop can be at different levels" and "deeper" to go to the next level:
>
>    variable
>       Queen : array 1 ..n of integer;
>
>    nest Column := 1 to n
>       for Queen[Column] := 1 to n do
>          if OkSoFar(Column) then
>             deeper;
>          end; -- if OkSoFar(Column)
>       end; -- for Queen[Column]
>    do
>       write(Queen[1..n]);
>    end;
>
> Of course, they would only rarely be useful.
>
>
> You can also use dimensions as a kind of meta-type to help type-safety and make sure that you don't make bad conversions.  E.g.:
>
>    dimension
>       area = distance * distance;
>       velocity = distance / time;
>    constant
>       mile = 5280 * foot;  -- foot is predeclared
>       acre = mile * mile / 640;
>    variable
>       d1, d2 : distance real;
>       a1 : area real;
>       v1 : velocity real;
>    (etc.)
>
> This might be useful in science and engineering.  In D it could be achieved using (string) typedefs and conversion macros so I don't imagine it would be worth adding.
>
>
> What do you think about these?