[Prev][Next][Index][Thread]

multiple values in a return from function

I'm not sure what I'm doing wrong here.  I wanted to return two values from
a function that computes solar positions--the right ascension and
declination of the sun.  Both are <floats>.  When I tried interactively
testing this function, it would only return 1 value.  I must be missing
something simple, but I don't get it.   If I change the function to return
an object that contains a right ascension slot and a declination slot, it
works fine.  If I return a list of the right ascension and declination, it
works too.

What Dylan concept do I need to bone up on?

I've included the source for illustration:


  **** This one works when tested interactively ****
define method compute-solar-position( epoch-day :: <integer> ) =>
  ( results :: <astro-position>)

   // Now pre-compute the important values based on epoch day
   ecliptic-obliquity := 23.4393 - 3.563e-7 * epoch-day;
   solar-eccentricity := 0.016709 - 1.151E-9 * epoch-day;
   solar-mean-anomaly := 356.0470 + 0.9856002585 * epoch-day;
   solar-arg-perihelion := 282.9404 + 4.70935E-5 * epoch-day;


  // compute eccentric anomaly in radians
  let eccentric-anomaly = solar-mean-anomaly +  (solar-eccentricity  *
                                           sin( solar-mean-anomaly ) *
                                           ( 1.0 + solar-eccentricity *
os( solar-mean-anomaly )));
  // compute x and y component of true anomaly position
  let x-true-anom       = cos( eccentric-anomaly ) - solar-eccentricity;
  let y-true-anom       = sqrt( 1.0 - solar-eccentricity ^ 2 ) *
in( eccentric-anomaly );

  let true-anomaly = atan2( y-true-anom , x-true-anom );

  // assume this is in AU?
  let solar-distance = sqrt( x-true-anom ^ 2  + y-true-anom ^ 2);

  // compute solar true longitude
  let solar-true-long = true-anomaly + solar-arg-perihelion;

   // compute solar ecliptic rectangular coordinates
  let x-sun = solar-distance * cos( solar-true-long );
  let y-sun = solar-distance * sin( solar-true-long );

  // now convert these to equatorial, rectangular coordinates
  let eq-x-sun = x-sun;
  let eq-y-sun = y-sun * cos( ecliptic-obliquity );
  let eq-z-sun = y-sun * sin( ecliptic-obliquity );

  let suns-pos = make( <astro-position> );
  // Finally, compute right ascension and declination
  suns-pos.right-ascension := atan2( eq-y-sun, eq-x-sun );
  suns-pos.declination     := atan2( eq-z-sun, sqrt( eq-x-sun ^ 2  +
eq-y-sun ^ 2));
  suns-pos;


end method;



  **** This one doesn't ****

define method compute-solar-position( epoch-day :: <integer> ) =>
  ( results :: false-or( <astro-position>))

   // Now pre-compute the important values based on epoch day
   ecliptic-obliquity := 23.4393 - 3.563e-7 * epoch-day;
   solar-eccentricity := 0.016709 - 1.151E-9 * epoch-day;
   solar-mean-anomaly := 356.0470 + 0.9856002585 * epoch-day;
   solar-arg-perihelion := 282.9404 + 4.70935E-5 * epoch-day;


  // compute eccentric anomaly in radians
  let eccentric-anomaly = solar-mean-anomaly +  (solar-eccentricity  *
                                           sin( solar-mean-anomaly ) *
                                           ( 1.0 + solar-eccentricity *
os( solar-mean-anomaly )));
  // compute x and y component of true anomaly position
  let x-true-anom       = cos( eccentric-anomaly ) - solar-eccentricity;
  let y-true-anom       = sqrt( 1.0 - solar-eccentricity ^ 2 ) *
in( eccentric-anomaly );

  let true-anomaly = atan2( y-true-anom , x-true-anom );

  // assume this is in AU?
  let solar-distance = sqrt( x-true-anom ^ 2  + y-true-anom ^ 2);

  // compute solar true longitude
  let solar-true-long = true-anomaly + solar-arg-perihelion;

   // compute solar ecliptic rectangular coordinates
  let x-sun = solar-distance * cos( solar-true-long );
  let y-sun = solar-distance * sin( solar-true-long );

  // now convert these to equatorial, rectangular coordinates
  let eq-x-sun = x-sun;
  let eq-y-sun = y-sun * cos( ecliptic-obliquity );
  let eq-z-sun = y-sun * sin( ecliptic-obliquity );

  // Finally, compute right ascension and declination
  let right-ascension = atan2( eq-y-sun, eq-x-sun );
  let declination       = atan2( eq-z-sun, sqrt( eq-x-sun ^ 2  + eq-y-sun ^
2));

   values( right-ascension, declination );
end method;
Follow-Ups: