% 99 bottles of beer, CHR(Prolog) version.
% tested in the K.U.Leuven CHR implementation in SWI-Prolog
% Mon Jun 19 14:22:05 2006 Jon Sneyers
% top-level goal: beer
:- use_module(library(chr)).
:- chr_constraint beer, beer(+int), bottle, sing,
capital, bottles, ofbeer, onwall, comma,
take_one, dotnl,
bottle_count, bottles(+int), writeresult.
:- chr_option(toplevel_show_store,off).
:- chr_option(optimize,full).
:- chr_option(debug,off).
% make 99 bottles and start singing
beer <=> beer(99), sing.
% make N bottles
makebottle @ beer(N) <=> N > 0 | bottle, beer(N-1).
endloop @ beer(_) <=> true.
% stop singing if we're already singing
% (change to simpagation rule to make the song infinite)
sing, sing <=> true.
% sing two lines
sing ==> capital, bottles, ofbeer, onwall, comma, bottles, ofbeer, dotnl,
take_one, comma, bottles, ofbeer, onwall, dotnl, nl.
% if we're still singing: sing again
sing <=> sing.
% take one bottle down
take_one, bottle <=> write('Take one down and pass it around').
% no more bottles: go to the store and start again
take_one <=> write('Go to the store and buy some more'), beer.
% print how many bottles there are in the store
bottle, bottle \ bottles <=> bottle_count, write(' bottles').
bottle \ bottles <=> write('1 bottle').
capital, bottles <=> write('No more bottles').
bottles <=> write('no more bottles').
% count the number of bottles in the store
bottle_count, bottle ==> bottles(1).
bottle_count <=> writeresult.
bottles(X), bottles(Y) <=> Z is X+Y, bottles(Z).
writeresult, bottles(N) <=> write(N).
% write stuff
onwall <=> write(' on the wall').
ofbeer <=> write(' of beer').
dotnl <=> write('.'), nl.
comma \ capital <=> true.
comma <=> write(', ').