Extract left factor

lab2/ll1.go

@@ -195,6 +195,9 @@ func ExtractLeftFactor() {
 					BodySize:   production.BodySize - len(extendFactor),
 					ID:         production.ID, // 可以循环利用，反正这个后面会删掉
 				}
+				if newProduction.BodySize == 0 {
+					newProduction.BodySymbol = []interface{}{&epsilonSymbol}
+				}
 				newSymbol.ProductionTable[index] = newProduction
 			}
 
@@ -202,12 +205,18 @@ func ExtractLeftFactor() {
 			index := 0
 			// 因为 prods 是按照 ProductionTable 的顺序排列的
 			// 所以可以直接用一个 index 一起
-			for originalIndex, production := range symbol.ProductionTable {
+			for originalIndex := 0; originalIndex < len(symbol.ProductionTable); originalIndex++ {
+				if index >= len(prods) {
+					break
+				}
+				production := symbol.ProductionTable[originalIndex]
 				if !cmp.Equal(production, prods[index]) {
 					continue
 				}
 				// 直接删掉
 				symbol.ProductionTable = append(symbol.ProductionTable[:originalIndex], symbol.ProductionTable[originalIndex+1:]...)
+				originalIndex--
+				index++
 			}
 			// 添加一个 A \to \alpha A'
 			symbol.ProductionTable = append(symbol.ProductionTable, &Production{

lab2/ll1_test.go

@@ -163,14 +163,17 @@ func initLeftFactorExample() {
 	// productions
 	// S -> if E then S | if E then S else S | Other
 	leftFactorExample.S.ProductionTable = append(leftFactorExample.S.ProductionTable, &Production{
+		ID:         0,
 		BodySize:   4,
 		BodySymbol: []interface{}{&leftFactorExample.If, &leftFactorExample.E, &leftFactorExample.Then, &leftFactorExample.S},
 	})
 	leftFactorExample.S.ProductionTable = append(leftFactorExample.S.ProductionTable, &Production{
+		ID:         1,
 		BodySize:   6,
 		BodySymbol: []interface{}{&leftFactorExample.If, &leftFactorExample.E, &leftFactorExample.Then, &leftFactorExample.S, &leftFactorExample.Else, &leftFactorExample.S},
 	})
 	leftFactorExample.S.ProductionTable = append(leftFactorExample.S.ProductionTable, &Production{
+		ID:         2,
 		BodySize:   1,
 		BodySymbol: []interface{}{&leftFactorExample.Other},
 	})
@@ -394,3 +397,25 @@ func TestBuildLL1AnalysisTable(t *testing.T) {
 		t.Error("F, ( = F -> ( E ) not found")
 	}
 }
+
+// 测试提取左因子
+func TestExtractLeftFactor(t *testing.T) {
+	GrammarSymbolTable = []interface{}{&leftFactorExample.S, &leftFactorExample.E, &leftFactorExample.If, &leftFactorExample.Else, &leftFactorExample.Other}
+	RootSymbol = &leftFactorExample.S
+
+	if !leftFactorExample.S.LeftFactored() {
+		t.Error("TestExtractLeftFactor failed")
+	}
+
+	ExtractLeftFactor()
+
+	for _, symbol := range GrammarSymbolTable {
+		if symbol, ok := symbol.(*NonTerminalSymbol); ok {
+			t.Log(symbol.String())
+		}
+	}
+
+	if leftFactorExample.S.LeftFactored() {
+		t.Error("TestExtractLeftFactor failed")
+	}
+}