master > master: codego - auslagern, erzeugungsmethode verbessert, SyntaxBaum -> Formula

codego/aussagenlogik/recursion/recursion_nnf.go

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+package recursion
+
+import (
+	"logik/aussagenlogik/formulae"
+)
+
+/* ---------------------------------------------------------------- *
+ * METHOD: compute NNF
+ * ---------------------------------------------------------------- */
+
+// NOTE: diese bedarf einer Art Doppeltrekursion
+func NNF(tree formulae.Formula) formulae.Formula {
+	// Definiere Schema:
+	var schema = func(tree formulae.Formula, prevValues []formulae.FormulaPair) formulae.FormulaPair {
+		// separate out positive and negative parts:
+		var pairs = formulae.NewFormulaPairs(prevValues)
+		var prevPos = pairs.Pos()
+		var prevNeg = pairs.Neg()
+		// compute value from previous positive/negative parts:
+		if tree.IsPositiveLiteral() {
+			return formulae.FormulaPair{
+				Pos: tree.Deepcopy(),
+				Neg: formulae.Negation(tree),
+			}
+		} else if tree.IsNegativeLiteral() {
+			return formulae.FormulaPair{
+				Pos: tree.Deepcopy(),
+				Neg: prevPos[0],
+			}
+		} else if tree.IsTautologySymbol() {
+			return formulae.FormulaPair{
+				Pos: formulae.Tautology,
+				Neg: formulae.Contradiction,
+			}
+		} else if tree.IsContradictionSymbol() {
+			return formulae.FormulaPair{
+				Pos: formulae.Contradiction,
+				Neg: formulae.Tautology,
+			}
+		} else if tree.IsNegation() {
+			return formulae.FormulaPair{
+				Pos: prevNeg[0],
+				Neg: prevPos[0],
+			}
+		} else if tree.IsConjunction2() {
+			return formulae.FormulaPair{
+				Pos: formulae.Conjunction2(prevPos[0], prevPos[1]),
+				Neg: formulae.Disjunction2(prevNeg[0], prevNeg[1]),
+			}
+		} else if tree.IsConjunction() {
+			return formulae.FormulaPair{
+				Pos: formulae.Conjunction(prevPos),
+				Neg: formulae.Disjunction(prevNeg),
+			}
+		} else if tree.IsDisjunction2() {
+			return formulae.FormulaPair{
+				Pos: formulae.Disjunction2(prevPos[0], prevPos[1]),
+				Neg: formulae.Conjunction2(prevNeg[0], prevNeg[1]),
+			}
+		} else if tree.IsDisjunction() {
+			return formulae.FormulaPair{
+				Pos: formulae.Disjunction(prevPos),
+				Neg: formulae.Conjunction(prevNeg),
+			}
+		} else if tree.IsImplication() {
+			return formulae.FormulaPair{
+				Pos: formulae.Implies(prevPos[0], prevPos[1]),
+				Neg: formulae.Conjunction2(prevPos[0], prevNeg[1]),
+			}
+		} else {
+			panic("Could not evaluate expression!")
+		}
+	}
+	// Erzeuge Funktion aus Schema und berechne Wert:
+	fn := formulae.CreateFromSchemeFmlPairValued(schema)
+	return fn(tree).Pos
+}