%
% astro2.pl -- prolog program to determine what you're looking at in
%              the night sky
%
% Brian "Beej" Hall
%
% to run, start prolog and do the following:
%
%    ?- consult(astro2).
%    ?- itsa(X).
%
% or, you could query a specific object to see if you have it right:
%
%    ?- itsa('inner planet').
%

%
% itsa/1: this is the predicate you look for matches in
%

itsa('galaxy') :- galaxy.
itsa('star') :- star.
itsa('planetoid') :- planetoid.
itsa('cluster') :- cluster.
itsa('nebula') :- nebula.
itsa('sun') :- sun.
itsa('moon') :- moon.
itsa('barred spiral galaxy') :- barred_spiral_galaxy.
itsa('spiral galaxy') :- spiral_galaxy.
itsa('elliptical galaxy') :- elliptical_galaxy.
itsa('irregular galaxy') :- irregular_galaxy.
itsa('sunlike') :- sunlike.
itsa('white dwarf') :- white_dwarf.
itsa('red giant') :- red_giant.
itsa('black hole') :- black_hole.
itsa('comet') :- comet.
itsa('asteroid') :- asteroid.
itsa('planet') :- planet.
itsa('inner planet') :- inner.
itsa('outer planet') :- outer.
itsa('open cluster') :- open.
itsa('globular cluster') :- globular.
itsa('emission nebula') :- emission.
itsa('planetary nebula') :- planetary.
itsa('dark') :- dark.

%
% definition of individual objects
% 

galaxy :- fuzzy, not(moves), not(individual_stars).
star :- point, not(moves).
planetoid :- moves.
cluster :- fuzzy, not(moves), individual_stars.
nebula :- fuzzy, not(individual_stars), not(moves).
sun :- large, bright, moves.
moon :- large, bright, crescent, moves.

spiral_galaxy :- galaxy, spiral.
barred_spiral_galaxy :- galaxy, bar.
elliptical_galaxy :- galaxy, elliptical.
irregular_galaxy :- galaxy, not(barred_spiral_galaxy), not(spiral_galaxy), not(elliptical_galaxy).

sunlike :- star, yellow.
white_dwarf :- star, white.
red_giant :- star, red.
black_hole :- star, black.

comet :- planetoid, fuzzy.
asteroid :- planetoid, point.
planet :- planetoid, disk.

inner :- planet, crescent.
outer :- planet, not(crescent).

open :- cluster, not(many_stars).
globular :- cluster, many_stars.

emission :- nebula, glowing, not(ring).
planetary :- nebula, glowing, ring.
dark :- nebula, not(glowing).

%
% These are the individual elements that the above objects are made of.
% The user is queried for each via the ask/1 predicate.
%

fuzzy :- ask('Does the object have a fuzzy appearance').
moves :- ask('Does the object appear to move against the stars').
point :- ask('Is the object a single point of light').
individual_stars :- ask('Can you resolve individual stars in the object').
large :- ask('Is the object larger than 2 degrees across').
bright :- ask('Is the object brighter than magnitude -8').
crescent :- ask('Does the object ever appear as a crescent').
spiral :- ask('Does the object have a spiral appearance').
bar :- ask('Does the object have a bar across its center').
elliptical :- ask('Does the object have an elliptical shape').
yellow :- ask('Is the object yellow').
white :- ask('Is the object white').
red :- ask('Is the object red').
black :- ask('Is the object black').
disk :- ask('Does the object appear as a disk').
many_stars :- ask('Does the object consist of more than 40 stars').
glowing :- ask('Is the object glowing').
ring :- ask('Is the object ring-shaped').

%
% asked/1: true for a question if is has already been asked.  (Don't
%          want to query the user twice for the same thing.)
%

asked('Does the object have a fuzzy appearance') :- fail.
asked('Does the object appear to move against the stars') :- fail.
asked('Is the object a single point of light') :- fail.
asked('Can you resolve individual stars in the object') :- fail.
asked('Is the object larger than 2 degrees across') :- fail.
asked('Is the object brighter than magnitude -8') :- fail.
asked('Does the object ever appear as a crescent') :- fail.
asked('Does the object have a spiral appearance') :- fail.
asked('Does the object have a bar across its center') :- fail.
asked('Does the object have an elliptical shape') :- fail.
asked('Is the object yellow') :- fail.
asked('Is the object white') :- fail.
asked('Is the object red') :- fail.
asked('Is the object black') :- fail.
asked('Does the object appear as a disk') :- fail.
asked('Does the object consist of more than 40 stars') :- fail.
asked('Is the object glowing') :- fail.

%
% ask/1: asks the user (if haven't asked already) one of the questions.
%

ask(Q) :- not(asked(Q)), assert(asked(Q)), write(Q), write('? '), read(yes), asserta(ask(Q)).

%
% yes and no--easier for the user to write than "true" and "fail".
%

yes :- true.
no :- fail.