flex Expert System Toolkit - LPIS

8. Run-Time Interpretation of KSL 110
Interpretation of KSL Sentences
Under the normal Prolog interpretation of relation calls, arguments are
treated as fixed objects which can only pattern-match with each other. This
interpretation is used wherever a $ symbol appears in a KSL program.
Under the flex interpretation of relation calls, however, arguments are
dereferenced immediately before the call is made. Furthermore, KSL objects
can be dereferenced to alternative values. For example, the construct
or([E 1
,…,E k
]) dereferences to some E i
where 1•i•k .
This interpretation means that backtracking can take place not only over
relation calls, but also over the dereferencing mechanism itself. For example,
consider the following call to the built-in predicate member/2.
member( X, [ 123, or([a,b,c]) ] ) .
Under a Prolog interpretation the possible solutions are
X = 123
X = or([a,b,c]) .
But under a flex interpretation there are 6 possible solutions :
X = 123
X = 123
X = 123
X = a
X = b
X = c
This is because the flex dereferencing mechanism generates three possible
Prolog goals from the original flex goal, namely:
member( X , [123,a] ) .
member( X , [123,b] ) .
member( X , [123,c] ) .
Each of these yields two solutions for X.
flex toolkit