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|
package lexer
import (
"fmt"
"strings"
"unicode/utf8"
)
const eof rune = -1
type Lexem struct {
Type lexType // Type of Lexem.
Value string // Value of Lexem.
Start int // Start position at input string.
End int // End position at input string.
}
//go:generate stringer -type=lexType
type lexType int
const (
LEOF lexType = iota
LError
LObjectStart
LObjectEnd
LObjectKey
LObjectValue
LArrayStart
LArrayEnd
LString
LNumber
LBoolean
LNull
)
// Lexer holds current scanner state.
type Lexer struct {
Input string // Input string.
Start int // Start position of current lexem.
Pos int // Pos at input string.
Output chan Lexem // Lexems channel.
width int // Width of last rune.
states stateStack // Stack of states to realize PrevState.
}
// newLexer returns new scanner for input string.
func NewLexer(input string) *Lexer {
return &Lexer{
Input: input,
Start: 0,
Pos: 0,
Output: make(chan Lexem, 2),
width: 0,
}
}
// Run lexing.
func (l *Lexer) Run(init stateFunc) {
for state := init; state != nil; {
state = state(l)
}
close(l.Output)
}
// PopState returns previous state function.
func (l *Lexer) PopState() stateFunc {
return l.states.Pop()
}
// PushState pushes state before going deeper states.
func (l *Lexer) PushState(s stateFunc) {
l.states.Push(s)
}
// Emit current lexem to output.
func (l *Lexer) Emit(typ lexType) {
l.Output <- Lexem{
Type: typ,
Value: l.Input[l.Start:l.Pos],
Start: l.Start,
End: l.Pos,
}
l.Start = l.Pos
}
// Errorf produces error lexem and stops scanning.
func (l *Lexer) Errorf(format string, args ...interface{}) stateFunc {
l.Output <- Lexem{
Type: LError,
Value: fmt.Sprintf(format, args...),
Start: l.Start,
End: l.Pos,
}
return nil
}
// Next rune from input.
func (l *Lexer) Next() (r rune) {
if int(l.Pos) >= len(l.Input) {
l.width = 0
return eof
}
r, l.width = utf8.DecodeRuneInString(l.Input[l.Pos:])
l.Pos += l.width
return r
}
// Back move position to previos rune.
func (l *Lexer) Back() {
l.Pos -= l.width
}
// Ignore previosly buffered text.
func (l *Lexer) Ignore() {
l.Start = l.Pos
l.width = 0
}
// Peek rune at current position without moving position.
func (l *Lexer) Peek() (r rune) {
r = l.Next()
l.Back()
return r
}
// Accept any rune from valid string. Returns true if Next rune was in valid string.
func (l *Lexer) Accept(valid string) bool {
if strings.ContainsRune(valid, l.Next()) {
return true
}
l.Back()
return false
}
// AcceptString returns true if given string was at position.
func (l *Lexer) AcceptString(s string, caseInsentive bool) bool {
input := l.Input[l.Start:]
if caseInsentive {
input = strings.ToLower(input)
s = strings.ToLower(s)
}
if strings.HasPrefix(input, s) {
l.width = 0
l.Pos += len(s)
return true
}
return false
}
// AcceptAnyOf substrings. Retuns true if any of substrings was found.
func (l *Lexer) AcceptAnyOf(s []string, caseInsentive bool) bool {
for _, substring := range s {
if l.AcceptString(substring, caseInsentive) {
return true
}
}
return false
}
// AcceptWhile passing symbols from input while they at `valid` string.
func (l *Lexer) AcceptWhile(valid string) bool {
isValid := false
for l.Accept(valid) {
isValid = true
}
return isValid
}
// AcceptWhileNot passing symbols from input while they NOT in `invalid` string.
func (l *Lexer) AcceptWhileNot(invalid string) bool {
isValid := false
for !strings.ContainsRune(invalid, l.Next()) {
isValid = true
}
l.Back()
return isValid
}
// AtStart returns true if current lexem not empty
func (l *Lexer) AtStart() bool {
return l.Pos == l.Start
}
|
