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package source
import (
"bufio"
"errors"
"io"
)
type Walker struct {
source *bufio.Reader
row int
col int
}
func NewWalker(source io.Reader) *Walker {
return &Walker{
source: bufio.NewReader(source),
row: 0,
col: 0,
}
}
func (w *Walker) Loc() Loc {
return Loc{
Row: w.row,
Col: w.col,
}
}
func (w *Walker) Next() (rune, bool, error) {
r, _, err := w.source.ReadRune()
if err != nil {
if errors.Is(err, io.EOF) {
return 0, true, nil
}
return 0, false, err
}
if r == '\n' {
w.row++
w.col = 0
} else {
w.col++
}
return r, false, nil
}
func (w *Walker) Consume(want rune) (bool, error) {
c, _, err := w.Next()
if err != nil {
return false, err
}
if c != want {
return true, ErrUnexpectedChar{
Expected: want,
Actual: c,
}
}
return true, nil
}
func (w *Walker) Peek() (rune, bool, error) {
r, _, err := w.source.ReadRune()
defer w.source.UnreadRune()
if err != nil {
if errors.Is(err, io.EOF) {
return 0, true, nil
}
return 0, false, err
}
return r, false, nil
}
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