75 lines
1.5 KiB
Go
75 lines
1.5 KiB
Go
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package grammar
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import (
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"bufio"
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"io"
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)
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// Reader is used for reading Runes from a stream.
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type Reader interface {
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// ReadRune reads the next Rune off the stream, or returns io.EOF.
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ReadRune() (Located[rune], error)
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// UnreadRune can be used to place a Rune onto an internal buffer, such that
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// the Rune will be the next to be read using ReadRune. If called multiple
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// times then ReadRune will produce the given Runes in LIFO order.
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UnreadRune(Located[rune])
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// NextLocation returns the Location of the next Rune which will be returned
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// with ReadRune.
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NextLocation() Location
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}
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type reader struct {
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br *bufio.Reader
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brNextLoc Location
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unread []Located[rune]
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}
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// NewReader wraps the io.Reader as a Reader. The given Reader should not be
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// read from after this call.
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func NewReader(r io.Reader) Reader {
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return &reader{
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br: bufio.NewReader(r),
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brNextLoc: Location{Row: 1, Col: 1},
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}
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}
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func (rr *reader) ReadRune() (Located[rune], error) {
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if len(rr.unread) > 0 {
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r := rr.unread[len(rr.unread)-1]
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rr.unread = rr.unread[:len(rr.unread)-1]
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return r, nil
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}
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loc := rr.brNextLoc
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r, _, err := rr.br.ReadRune()
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if err != nil {
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return Located[rune]{}, err
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}
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if r == '\n' {
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rr.brNextLoc.Row++
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rr.brNextLoc.Col = 1
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} else {
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rr.brNextLoc.Col++
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}
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return Located[rune]{loc, r}, nil
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}
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func (rr *reader) UnreadRune(r Located[rune]) {
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rr.unread = append(rr.unread, r)
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}
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func (rr *reader) NextLocation() Location {
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if len(rr.unread) > 0 {
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return rr.unread[len(rr.unread)-1].Location
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}
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return rr.brNextLoc
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}
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