For Want of a Nail.pl

itemlost_becauseof(shoe, nail).
itemlost_becauseof(horse, shoe).
itemlost_becauseof(rider, horse).
itemlost_becauseof(battle, rider).
itemlost_becauseof(kingdom, battle).

write_poem(ItemLost) :-
    write_poem_aux(ItemLost);
    write_last_line(ItemLost).

write_poem_aux(ItemLost) :-
    itemlost_becauseof(Impacted, ItemLost),
    write_line(ItemLost, Impacted),
    write_poem_aux(Impacted).

write_line(Item, Impacted) :-
    write("For want of a "), write(Item), write(" a "), write(Impacted), write(" was lost;"), nl.

write_last_line(Item) :-
    write("And all for the want of a "), write(Item), write("."), nl.

%% Example poem (try in a Prolog repl)
?- write_poem(horse).

%% Root cause and impact
loss_rootcause(ItemLost, Cause) :- 
    itemlost_becauseof(ItemLost, Z), loss_rootcause(Z, Cause), !.
loss_rootcause(ItemLost, Cause) :- 
    itemlost_becauseof(ItemLost, Cause).

item_impacted(Cause, ItemLost) :-
    itemlost_becauseof(ItemLost, Cause).
item_impacted(Cause, ItemLost) :-
    itemlost_becauseof(ItemLost, X),
    item_impacted(Cause, X).
    
%% To find the root cause on kindom's downfall
?- loss_rootcause(kingdom, RootCause).
   
%% To find the impact of a missing nail
?- findall(X, item_impacted(nail, X), NailImpacted).

%% Annotated names
annotated_name(nail,  horse-nail).
annotated_name(X,  X).

write_annotated(X) :-
    annotated_name(X, Annotated), write(Annotated).
   
% write_last_line(Item) :-
%     write("And all for the want of a "), write_annotated(Item), write("."), nl.