func TestNNF(t *testing.T) {
// Build a simple BNF aGrammar description aGrammar.
gb := parser.OpenGrammarBuilder()
gb.Name("a4").
Terminals("a").
Nonterminals("S", "A", "E").
Rule().Lhs("`*").Rhs("S", "`.").
Rule().Lhs("S").Rhs("A", "A", "A", "A").
Rule().Lhs("A").Rhs("a").
Rule().Lhs("A").Rhs("E").
Rule().Lhs("E").Rhs("`e")
g, err := gb.Build()
if err != nil {
t.Error(err)
return
}
var aGrammar parser.Grammar
var rTransform parser.SyntaxTreeTransform
nnf, err := IsNihilisticNormalForm(g)
if err != nil {
t.Error()
return
}
if !nnf {
fmt.Println("Grammar is not NNF, transforming.")
aGrammar, rTransform, err = GetNihilisticAugmentGrammar(g)
if err != nil {
t.Error(err)
return
}
} else {
t.Error("Grammar returned NNF.")
return
}
fmt.Println("Name: " + aGrammar.Name())
terms := make([]string, aGrammar.NumTerminals())
for i, t := range aGrammar.Terminals() {
terms[i] = t.String()
}
nterms := make([]string, aGrammar.NumNonterminals())
for i, t := range aGrammar.Nonterminals() {
nterms[i] = t.String()
}
fmt.Println("Terminals: " + strings.Join(terms, ", "))
fmt.Println("Nonterminals: " + strings.Join(nterms, ", "))
fmt.Println("Productions:")
for _, p := range aGrammar.Productions() {
fmt.Println(" " + p.String())
}
rTransform = rTransform
}
func GetNihilisticAugmentGrammar(g parser.Grammar) (parser.Grammar, parser.SyntaxTreeTransform, error) {
exceptionalEpsilons := []parser.GrammarParticle{}
idxg := parser.GetIndexedGrammar(g)
idx, err := idxg.GetIndex(index.BASIC_INDEX)
if err != nil {
return nil, nil, err
}
bidx := idx.(*index.BasicGrammarIndex)
idx, err = idxg.GetIndex(index.NAME_INDEX)
if err != nil {
return nil, nil, err
}
nidx := idx.(*index.NameIndex)
for _, nt := range idxg.Nonterminals() {
n, err := IsNihilistic(nt)
if err != nil {
return nil, nil, err
}
if bidx.Epsilon(nt) && !n {
exceptionalEpsilons = append(exceptionalEpsilons, nt)
}
}
gb := parser.OpenGrammarBuilder()
for _, nt := range g.Nonterminals() {
if nt.Asterisk() {
continue
}
gb.Nonterminals(nt.Name())
}
for _, t := range g.Terminals() {
if t.Epsilon() {
continue
}
gb.Terminals(t.Name())
}
augmentMap := make(map[string]string)
invMap := make(map[string]string)
for _, e := range exceptionalEpsilons {
eName := e.Name() + "-ε"
augmentMap[e.Name()] = eName
invMap[eName] = e.Name()
gb.Nonterminals(eName)
//gb.Rule().Lhs(eName).Rhs("`e")
}
for _, nt := range g.Nonterminals() {
for i := 0; i < bidx.NumLhsStarts(nt); i++ {
prod := bidx.LhsStart(nt, i)
//fmt.Printf("LHSTART(%s,%d): %s\n", nt.String(), i, prod.String())
exIdx := []int{}
rhs := []string{}
for j := 0; j < prod.RhsLen(); j++ {
t := prod.Rhs(j)
if _, has := augmentMap[t.Name()]; has {
exIdx = append(exIdx, j)
//fmt.Println("exidx gets "+t.String())
}
rhs = append(rhs, t.Name())
}
if nt.Asterisk() { // Initial rule is special-cased.
//fmt.Println("rule transfers: "+prod.String())
//fmt.Println("Args: {"+prod.Lhs(0).Name()+"}, {"+strings.Join(rhs,",")+"}")
gb.Rule().Lhs(prod.Lhs(0).Name()).Rhs(rhs...)
initSym := nidx.Nonterminal(rhs[0])
if initSym != nil {
if bidx.Epsilon(initSym) {
gb.Rule().Lhs(initSym.Name()).Rhs(augmentMap[initSym.Name()])
}
}
} else {
rhsinst := make([]string, len(rhs))
//fmt.Printf("index len %d\n", len(exIdx))
s := cnt.FirstSelection(uint(len(exIdx)))
for {
nnCount := 0
for j := 0; j < len(rhs); j++ {
rhsinst[j] = rhs[j]
if nidx.Terminal(rhs[j]) != nil {
nnCount++
} else {
nt := nidx.Nonterminal(rhs[j])
nihil, err := IsNihilistic(nt)
if err != nil {
return nil, nil, err
}
if !nihil {
nnCount++
}
}
}
copy(rhsinst, rhs)
for j := 0; j < len(exIdx); j++ {
if s.Test(j) {
//fmt.Printf("idx %d replacement: %s->%s\n", exIdx[j], rhsinst[exIdx[j]], augmentMap[rhsinst[exIdx[j]]])
rhsinst[exIdx[j]] = augmentMap[rhsinst[exIdx[j]]]
nnCount--
}
}
var head string
if nnCount == 0 {
head = augmentMap[prod.Lhs(0).Name()]
} else {
head = prod.Lhs(0).Name()
}
//fmt.Println("rule transforms: "+prod.String())
//fmt.Println("Args: {"+head+"}, {"+strings.Join(rhs,",")+"}")
gb.Rule().Lhs(head).Rhs(rhsinst...)
if s.HasNext() {
s = s.Next()
} else {
break
}
}
}
}
}
gb.Name(g.Name() + "-ε")
augmentedGrammar, err := gb.Build()
if err != nil {
return nil, nil, err
}
augidx := parser.GetIndexedGrammar(augmentedGrammar)
idx, err = augidx.GetIndex(index.NAME_INDEX)
if err != nil {
return nil, nil, err
}
anidx := idx.(*index.NameIndex)
idx, err = augidx.GetIndex(index.BASIC_INDEX)
if err != nil {
return nil, nil, err
}
abidx := idx.(*index.BasicGrammarIndex)
reverseMap := make(map[parser.GrammarParticle]parser.GrammarParticle)
for k, v := range augmentMap {
reverseMap[anidx.Nonterminal(v)] = nidx.Nonterminal(k)
}
prodMap := make(map[parser.Production]parser.Production)
for _, p := range augmentedGrammar.Productions() {
// Ignore the special case start rule for grammars that accept nil input.
if p.LhsLen() == 1 && p.RhsLen() == 1 {
initSym := abidx.LhsStart(augmentedGrammar.Asterisk(), 0).Rhs(0)
if p.Lhs(0) == initSym && invMap[p.Rhs(0).Name()] == initSym.Name() {
continue
}
}
if p.RhsLen() == 1 && p.Rhs(0).Epsilon() {
continue
}
rhs := make([]string, 0, p.RhsLen())
for i := 0; i < p.RhsLen(); i++ {
rp := p.Rhs(i)
if ot, has := reverseMap[rp]; has {
rhs = append(rhs, ot.Name())
} else {
rhs = append(rhs, rp.Name())
}
}
//fmt.Printf("Searching for preimage rhs %s\n", strings.Join(rhs,","))
var target parser.Production
for _, cp := range nidx.RhsNames(rhs) {
//fmt.Println(" considering "+cp.String())
//for _, p := range g.Productions() {
//fmt.Println(p.String())
//}
if nt, has := reverseMap[p.Lhs(0)]; has {
if cp.Lhs(0) == nt {
target = cp
break
}
} else {
if cp.Lhs(0).Name() == p.Lhs(0).Name() {
target = cp
break
}
}
}
if target == nil {
return nil, nil, errors.New("Could not find preimage of augmented production rule: " + p.String())
}
prodMap[p] = target
}
var rtrans func(treeNode parser.SyntaxTreeNode) (parser.SyntaxTreeNode, error)
rtrans = func(treeNode parser.SyntaxTreeNode) (parser.SyntaxTreeNode, error) {
part := treeNode.Part()
if op, has := reverseMap[part]; has {
part = op
}
exp := make([]parser.SyntaxTreeNode, treeNode.NumChildren())
for i := 0; i < len(exp); i++ {
st := treeNode.Child(i)
if _, has := reverseMap[st.Part()]; has {
r, err := rtrans(st)
if err != nil {
return nil, err
}
exp[i] = r
} else {
exp[i] = st
}
}
return &parser.BasicSyntaxTreeNode{
Particle: part,
FirstTokenIdx: treeNode.First(),
LastTokenIdx: treeNode.Last(),
SyntacticValue: treeNode.Value(),
Prod: prodMap[treeNode.Rule()],
Expansion: exp,
}, nil
}
return augmentedGrammar, rtrans, nil
}