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grammar.go
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grammar.go
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package lr0
import (
"fmt"
"github.com/pkg/errors"
)
//// Grammar defines full grammar how to parse an input stream
//type Grammar interface {
// Lexer
// RulesCount() int
// Rule(index int) Rule
// // MainRule returns main rule, the one with EOF flag
// MainRule() Rule
// // RulesFor returns set of rules for the given subject
// RulesFor(id Id) []Rule
//}
// newGrammar creates new Grammar
//
// Violation of the following statements will cause panic ErrDefine since
// it is definition mistake.
//
// - All Terminal must be used in Rules. No unused Terminals.
//
// - Every Id in every rule definition must exist either in Terminals or
// in Rules Subject
//
// - Exactly one Rule must have EOF flag - this is Main Rule
func newGrammar(terminals []Terminal, nonTerminals []NonTerminalDefinition) *grammar {
var (
l = newLexer(terminals...)
nonTerm = make(map[Id]Symbol)
mainS Symbol
ruleIndex int
si = make(map[Id][]int)
furtherNTAt = make(map[Id]string)
usedT = make(map[Id]struct{})
)
gr := &grammar{
lexer: l,
nonTerm: nonTerm,
rules: make([]Rule, 0),
mainIndex: -1,
subjectsIndices: si,
}
for _, ntDef := range nonTerminals {
subjId := ntDef.Id()
nonTerm[subjId] = ntDef
delete(furtherNTAt, subjId)
if subjId == InvalidId {
panic(errors.Wrapf(ErrDefine, "Non-Terminal %s id is zero", dumpSymbol(ntDef)))
}
if l.IsTerminal(subjId) {
panic(errors.Wrapf(ErrDefine, "Non-Terminal %s is Terminal", dumpSymbol(ntDef)))
}
for ri, r := range ntDef.GetRules(gr) {
if r.HasEOF() {
if mainS != nil {
panic(errors.Wrapf(ErrDefine, "another rule %s has Main flag too, previous was %s", dumpSymbol(ntDef), dumpSymbol(mainS)))
}
mainS = ntDef
gr.mainIndex = ruleIndex
}
si[subjId] = append(si[subjId], ruleIndex)
// now this non-terminal is defined
gr.rules = append(gr.rules, r)
ruleIndex++
for i, id := range r.Definition() {
// defined Terminal - ok
if l.IsTerminal(id) {
usedT[id] = struct{}{}
continue
}
// already defined non-terminal - ok
if _, ok := si[id]; ok {
continue
}
// already know where it was seen first time - ok
if _, ok := furtherNTAt[id]; ok {
continue
}
// seeing this non-terminal first time
furtherNTAt[id] = fmt.Sprintf("#%d in NT %s rules[%d] (%s) definitions[%d]", id, dumpSymbol(ntDef), ri, r, i)
}
}
}
if len(furtherNTAt) != 0 {
msg := "undefined non-terminals without rules:\n"
for _, at := range furtherNTAt {
msg += "- " + at + "\n"
}
panic(errors.Wrap(ErrDefine, msg))
}
if gr.mainIndex == -1 {
panic(errors.Wrap(ErrDefine, "no main rule with EOF flag"))
}
if len(usedT) != len(terminals) {
msg := "following Terminals are not used in any Rule:\n"
bad := false
for _, t := range terminals {
if t.Id() < 0 {
continue
}
if _, ok := usedT[t.Id()]; ok {
continue
}
msg += "- " + dumpSymbol(t) + "\n"
bad = true
}
if bad {
panic(errors.Wrap(ErrDefine, msg))
}
}
return gr
}
type grammar struct {
*lexer
nonTerm map[Id]Symbol
rules []Rule
mainIndex int
subjectsIndices map[Id][]int
}
func (g *grammar) SymbolName(id Id) string {
if n := g.lexer.SymbolName(id); n != "" {
return n
}
if s, ok := g.nonTerm[id]; ok {
return s.Name()
}
return ""
}
func (g *grammar) RulesCount() int { return len(g.rules) }
func (g *grammar) Rule(index int) Rule { return g.rules[index] }
func (g *grammar) MainRule() Rule {
return g.rules[g.mainIndex]
}
func (g *grammar) RulesFor(id Id) []Rule {
indices, ok := g.subjectsIndices[id]
if !ok {
if g.IsTerminal(id) {
panic(errors.Wrapf(ErrDefine, "no rule - %s is Terminal", dumpId(id, g)))
}
panic(errors.Wrapf(ErrDefine, "no rule for #%d", id))
}
ret := make([]Rule, 0, len(indices))
for _, idx := range indices {
ret = append(ret, g.rules[idx])
}
return ret
}