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|
package grammar
import (
"fmt"
)
type ActionType string
const (
ActionTypeShift = ActionType("shift")
ActionTypeReduce = ActionType("reduce")
ActionTypeError = ActionType("error")
)
type actionEntry int
const actionEntryEmpty = actionEntry(0)
func newShiftActionEntry(state stateNum) actionEntry {
return actionEntry(state * -1)
}
func newReduceActionEntry(prod productionNum) actionEntry {
return actionEntry(prod)
}
func (e actionEntry) isEmpty() bool {
return e == actionEntryEmpty
}
func (e actionEntry) describe() (ActionType, stateNum, productionNum) {
if e == actionEntryEmpty {
return ActionTypeError, stateNumInitial, productionNumNil
}
if e < 0 {
return ActionTypeShift, stateNum(e * -1), productionNumNil
}
return ActionTypeReduce, stateNumInitial, productionNum(e)
}
type GoToType string
const (
GoToTypeRegistered = GoToType("registered")
GoToTypeError = GoToType("error")
)
type goToEntry uint
const goToEntryEmpty = goToEntry(0)
func newGoToEntry(state stateNum) goToEntry {
return goToEntry(state)
}
func (e goToEntry) isEmpty() bool {
return e == goToEntryEmpty
}
func (e goToEntry) describe() (GoToType, stateNum) {
if e == goToEntryEmpty {
return GoToTypeError, stateNumInitial
}
return GoToTypeRegistered, stateNum(e)
}
type ParsingTable struct {
actionTable []actionEntry
goToTable []goToEntry
stateCount int
terminalCount int
nonTerminalCount int
InitialState stateNum
}
func (t *ParsingTable) getAction(state stateNum, sym symbolNum) (ActionType, stateNum, productionNum) {
pos := state.Int()*t.terminalCount + sym.Int()
return t.actionTable[pos].describe()
}
func (t *ParsingTable) getGoTo(state stateNum, sym symbolNum) (GoToType, stateNum) {
pos := state.Int()*t.nonTerminalCount + sym.Int()
return t.goToTable[pos].describe()
}
func (t *ParsingTable) writeShiftAction(state stateNum, sym symbol, nextState stateNum) error {
pos := state.Int()*t.terminalCount + sym.num().Int()
act := t.actionTable[pos]
if !act.isEmpty() {
ty, _, _ := act.describe()
if ty == ActionTypeReduce {
return fmt.Errorf("shift/reduce conflict")
}
}
t.actionTable[pos] = newShiftActionEntry(nextState)
return nil
}
func (t *ParsingTable) writeReduceAction(state stateNum, sym symbol, prod productionNum) error {
pos := state.Int()*t.terminalCount + sym.num().Int()
act := t.actionTable[pos]
if !act.isEmpty() {
ty, _, p := act.describe()
if ty == ActionTypeReduce && p != prod {
return fmt.Errorf("reduce/reduce conflict")
}
return fmt.Errorf("shift/reduce conflict")
}
t.actionTable[pos] = newReduceActionEntry(prod)
return nil
}
func (t *ParsingTable) writeGoTo(state stateNum, sym symbol, nextState stateNum) {
pos := state.Int()*t.nonTerminalCount + sym.num().Int()
t.goToTable[pos] = newGoToEntry(nextState)
}
func genSLRParsingTable(automaton *lr0Automaton, prods *productionSet, follow *followSet, termCount, nonTermCount int) (*ParsingTable, error) {
var ptab *ParsingTable
{
initialState := automaton.states[automaton.initialState]
ptab = &ParsingTable{
actionTable: make([]actionEntry, len(automaton.states)*termCount),
goToTable: make([]goToEntry, len(automaton.states)*nonTermCount),
stateCount: len(automaton.states),
terminalCount: termCount,
nonTerminalCount: nonTermCount,
InitialState: initialState.num,
}
}
for _, state := range automaton.states {
for sym, kID := range state.next {
nextState := automaton.states[kID]
if sym.isTerminal() {
err := ptab.writeShiftAction(state.num, sym, nextState.num)
if err != nil {
return nil, err
}
} else {
ptab.writeGoTo(state.num, sym, nextState.num)
}
}
for prodID := range state.reducible {
prod, _ := prods.findByID(prodID)
flw, err := follow.find(prod.lhs)
if err != nil {
return nil, err
}
for sym := range flw.symbols {
err := ptab.writeReduceAction(state.num, sym, prod.num)
if err != nil {
return nil, err
}
}
if flw.eof {
err := ptab.writeReduceAction(state.num, symbolEOF, prod.num)
if err != nil {
return nil, err
}
}
}
}
return ptab, nil
}
|
