rules2Prereq function

DefaultMap<Logic, Set<Logic>> rules2Prereq(DefaultMap<(Logic, bool), Set<(Logic, bool)>> rules)

build prerequisites table from rules

Description by example

given set of logic rules:

a -> b, c b -> c

we build prerequisites (from what points something can be deduced):

b <- a c <- a, b

rules: {} of a -> b, c, ... return: {} of c <- a, b, ...

Note however, that these prerequisites may not be enough to prove a fact. An example is 'a -> b' rule, where prereq(a) is b, and prereq(b) is a. That's because a=T -> b=T, and b=F -> a=F, but a=F -> b=?

Implementation

DefaultMap<Logic, Set<Logic>> rules2Prereq(
    DefaultMap<(Logic, bool), Set<(Logic, bool)>> rules) {
  final prereq = DefaultMap<Logic, Set<Logic>>(() => <Logic>{});
  for (final entry in rules.entries) {
    final (key, impl) = (entry.key, entry.value);
    var (a, _) = key;
    if (a is Not) {
      a = a.arg;
    }
    for (var (i, _) in impl) {
      if (i is Not) {
        i = i.arg;
      }
      if (!prereq.containsKey(i)) {
        prereq[i] = <Logic>{};
      }
      prereq[i].add(a);
    }
  }
  return prereq;
}