Obtaining More Solutions

• Backtracking used for obtaining multiple solutions
• Results obtained one by one which meet the requirements of a single goal
• Each time we generate a new solution - we need to overwrite the previous one
  Variable binding to one solution - then another - and so on until all solutions have been obtained
• However, sometimes prefer to have all the generated objects available together - into a List
• This is achieved in Prolog, using bagof and setof
• Some Prolog implementations provide findall

miles(sketches_of_spain).
miles(aura).
miles(do_bop).
miles(tutu).
miles(amandala).
miles(a_kind_of_blue).

jones(back_on_the_block).
jones(right_thing).
jones(swing).

Q: miles(X)
A: X = sketches_of_spain

Then need to explicitly ask for more solutions to the query - in which case it fails backtracking result and repeats the query starting from the point where the last call was satisfied.

A : X = aura

However, if we issue the query :

Q: findall(X,miles(X),L)  
A: X = _34 ; L = [ sketches_of_spain, aura, 
 do_bop, tutu, amandala, a_kind_of_blue ]

 
• findall
• bagof or setof
• Removing duplicate items with setof