% $Id: ChoiceExamples.oz,v 1.2 2008/12/03 17:14:15 leavens Exp leavens $
\insert 'SolveFirst.oz'
declare

proc {Vowel ?R}
   choice
      R=a
   [] R=e
   [] R=i
   [] R=o
   [] R=u
   end
end

% Solve returns a lazy List
L = {Solve Vowel}
{Browse L}
{Delay 5000}
_={List.take L 2}

% A choice suspends if used directly
% {Browse {Vowel $}}

% But can be used in a search with Solve
{Browse {List.take {Solve Vowel} 4}}

% fail continues with next alternative of most recent choice

declare
proc {Distinct ?Res}
   V1 V2
in
   {Vowel V1}
   {Vowel V2}
   if V1 == V2 then fail end
   Res=V1#V2
end

{Browse {List.take {Solve Distinct} 7}}
{Browse {List.take {Solve proc {$ ?Z} {Distinct Z} end} 15}}
{Browse {List.take {Solve Distinct} 21}}