Introduction

ScalaLogic is a light-weight Prolog interpreter written in Scala.

It can parse and execute Prolog code or it can write logic programs in a Prolog-like DSL language inside Scala. Emphasis is on simplicity, not performance. Most standard library predicates are not supported but can easily be added.

Example

Define the theory in the DSL language:

  val append = 'append
  val quicksort = 'quicksort
  val partition = 'partition
  
  val theory = scalog(
        //Quicksort
    	quicksort(Nil, Nil),
    	quicksort('HEAD ::'TAIL,'SORTED) := partition('HEAD,'TAIL,'LEFT,'RIGHT) &
                                    		quicksort('LEFT,'SORTEDL) &
                                    		quicksort('RIGHT,'SORTEDR) &
                                    		append('SORTEDL,'HEAD ::'SORTEDR,'SORTED),
        
        //Partition
        partition('PIVOT, Nil, Nil, Nil),
        partition('PIVOT,'HEAD ::'TAIL,'HEAD::'LEFT,'RIGHT) :='HEAD < 'PIVOT &
                                                         	   partition('PIVOT,'TAIL,'LEFT,'RIGHT),
        partition('PIVOT,'HEAD ::'TAIL,'LEFT,'HEAD ::'RIGHT) :='HEAD >= 'PIVOT &
                                                         	    partition('PIVOT, 'TAIL, 'LEFT, 'RIGHT),
        
        //Append
        append(Nil, 'L, 'L),
        append('H ::'L1,'L2,'H ::'L3) := append('L1,'L2,'L3)
  )

Execute a goal:

  val solutions = 
    theory ?= quicksort(List(3,2,1,10,8,9,7,5,6,4,3,2,1,10,8,9,7,5,6,4,3), 'Sorted)

Print each solution in the Stream:

  print(solutions)

  Sorted = [1,1,2,2,3,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10].