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|
package compiler
import (
"bytes"
"errors"
"fmt"
"io"
)
type SyntaxError struct {
message string
}
func (err *SyntaxError) Error() string {
return fmt.Sprintf("Syntax Error: %v", err.message)
}
func raiseSyntaxError(message string) {
panic(&SyntaxError{
message: message,
})
}
type symbolTable struct {
symPos2Byte map[symbolPosition]byte
endPos2ID map[symbolPosition]int
}
func genSymbolTable(root astNode) *symbolTable {
symTab := &symbolTable{
symPos2Byte: map[symbolPosition]byte{},
endPos2ID: map[symbolPosition]int{},
}
return genSymTab(symTab, root)
}
func genSymTab(symTab *symbolTable, node astNode) *symbolTable {
if node == nil {
return symTab
}
switch n := node.(type) {
case *symbolNode:
symTab.symPos2Byte[n.pos] = n.value
case *endMarkerNode:
symTab.endPos2ID[n.pos] = n.id
default:
left, right := node.children()
genSymTab(symTab, left)
genSymTab(symTab, right)
}
return symTab
}
func parse(regexps map[int][]byte) (astNode, *symbolTable, error) {
if len(regexps) == 0 {
return nil, nil, fmt.Errorf("parse() needs at least one token entry")
}
var root astNode
for id, re := range regexps {
if len(re) == 0 {
return nil, nil, fmt.Errorf("regular expression must be a non-empty byte sequence")
}
p := newParser(id, bytes.NewReader(re))
n, err := p.parse()
if err != nil {
return nil, nil, err
}
if root == nil {
root = n
} else {
root = newAltNode(root, n)
}
}
positionSymbols(root, 1)
return root, genSymbolTable(root), nil
}
type parser struct {
id int
lex *lexer
peekedTok *token
lastTok *token
}
func newParser(id int, src io.Reader) *parser {
return &parser{
id: id,
lex: newLexer(src),
peekedTok: nil,
lastTok: nil,
}
}
func (p *parser) parse() (astNode, error) {
return p.parseRegexp()
}
func (p *parser) parseRegexp() (ast astNode, retErr error) {
defer func() {
err := recover()
if err != nil {
retErr = err.(error)
var synErr SyntaxError
if !errors.Is(retErr, &synErr) {
panic(err)
}
return
}
}()
alt := p.parseAlt()
p.expect(tokenKindEOF)
return newConcatNode(alt, newEndMarkerNode(p.id, symbolPositionNil)), nil
}
func (p *parser) parseAlt() astNode {
left := p.parseConcat()
for {
if !p.consume(tokenKindAlt) {
break
}
right := p.parseConcat()
left = newAltNode(left, right)
}
return left
}
func (p *parser) parseConcat() astNode {
left := p.parseRepeat()
for {
right := p.parseRepeat()
if right == nil {
break
}
left = newConcatNode(left, right)
}
return left
}
func (p *parser) parseRepeat() astNode {
group := p.parseGroup()
if !p.consume(tokenKindRepeat) {
return group
}
return newRepeatNode(group)
}
func (p *parser) parseGroup() astNode {
if p.consume(tokenKindGroupOpen) {
defer p.expect(tokenKindGroupClose)
return p.parseAlt()
}
if !p.consume(tokenKindChar) {
return nil
}
b := []byte(string(p.lastTok.char))
switch len(b) {
case 1:
return newSymbolNode(p.lastTok, b[0], symbolPositionNil)
case 2:
return newConcatNode(
newSymbolNode(p.lastTok, b[0], symbolPositionNil),
newSymbolNode(p.lastTok, b[1], symbolPositionNil),
)
case 3:
return newConcatNode(
newConcatNode(
newSymbolNode(p.lastTok, b[0], symbolPositionNil),
newSymbolNode(p.lastTok, b[1], symbolPositionNil),
),
newSymbolNode(p.lastTok, b[2], symbolPositionNil),
)
default: // is equivalent to case 4
return newConcatNode(
newConcatNode(
newConcatNode(
newSymbolNode(p.lastTok, b[0], symbolPositionNil),
newSymbolNode(p.lastTok, b[1], symbolPositionNil),
),
newSymbolNode(p.lastTok, b[2], symbolPositionNil),
),
newSymbolNode(p.lastTok, b[3], symbolPositionNil),
)
}
}
func (p *parser) expect(expected tokenKind) {
if !p.consume(expected) {
tok := p.peekedTok
errMsg := fmt.Sprintf("unexpected token; expected: %v, actual: %v", expected, tok.kind)
raiseSyntaxError(errMsg)
}
}
func (p *parser) consume(expected tokenKind) bool {
var tok *token
var err error
if p.peekedTok != nil {
tok = p.peekedTok
p.peekedTok = nil
} else {
for {
tok, err = p.lex.next()
if err != nil {
panic(err)
}
break
}
}
p.lastTok = tok
if tok.kind == expected {
return true
}
p.peekedTok = tok
p.lastTok = nil
return false
}
|
