/*
Apply Disjunctive Normal Form.
Convert ANDs of ORs to ORs of ANDs. For example:
(A OR B) AND C => (A AND C) OR (B AND C)
Also apply constant folding. Remove any constant terms.
*/
func (this *DNF) VisitAnd(expr *expression.And) (interface{}, error) {
err := expr.MapChildren(this)
if err != nil {
return nil, err
}
// Constant folding
var terms expression.Expressions
for _, term := range expr.Operands() {
val := term.Value()
if val == nil {
if terms == nil {
terms = make(expression.Expressions, 0, len(expr.Operands()))
}
terms = append(terms, term)
continue
}
if !val.Truth() {
return expression.FALSE_EXPR, nil
}
}
if len(terms) == 0 {
return expression.TRUE_EXPR, nil
}
if len(terms) < len(expr.Operands()) {
expr = expression.NewAnd(terms...)
}
// DNF
if dnfComplexity(expr, 16) >= 16 {
return expr, nil
} else {
return applyDNF(expr, 0), nil
}
}
