|
|
pl:prolog:pllib:rule_interpreter_3 [2019/06/27 15:50] |
pl:prolog:pllib:rule_interpreter_3 [2019/06/27 15:50] (aktualna) |
| ====== Rule interpreter 3 ====== |
| {{tag>rule interpreter framework}} |
| ===== Description ===== |
| A skeleton two-level rule interpreter |
| |
| **Source**: The Art of Prolog |
| ===== Download ===== |
| Program source code: {{rule_interpreter_3.pl}} |
| ===== Listing ===== |
| <code prolog> |
| /* |
| monitor(Goal) :- |
| Succeeds if a result of yes is returned from solving Goal |
| at the solve level, or when the end of the computation is reached. |
| */ |
| |
| :- op(40,xfy,&). |
| :- op(30,xf,is_true). |
| |
| monitor(Goal) :- solve(Goal,Result), filter(Result). |
| monitor(Goal). |
| |
| filter(yes). |
| % filter(no) fail. |
| |
| /* |
| solve(Goal,Result) :- |
| Given a set of rules of the form rule(A,B,Name), Goal has |
| Result yes if it follows from the rules and no if it does not. |
| */ |
| solve(A,yes) :- fact(A). |
| solve(A,Result) :- rule(A,B,Name), solve_body(B,Result). |
| solve(A,no). |
| |
| solve_body(A&B,Result) :- |
| solve(A,ResultA), solve_and(ResultA,B,Result). |
| solve_body(A is_true,Result) :- solve(A,Result). |
| |
| solve_and(no,A,no). |
| solve_and(yes,B,Result) :- solve(B,Result). |
| |
| % Program 17.18: A skeleton two-level rule interpreter |
| </code> |
| ===== Comments ===== |
| |