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source.go
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source.go
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// Copyright (c) 2011 CZ.NIC z.s.p.o. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// blame:
// jnml, labs.nic.cz
// Miek Gieben, SIDN, miek@miek.nl
package lexer
import (
"go/token"
"io"
)
// EOFReader implements a RuneReader allways returning 0 (EOF)
type EOFReader int
func (r EOFReader) ReadRune() (arune rune, size int, err error) {
return 0, 0, io.EOF
}
type source struct {
reader io.RuneReader
position token.Position
}
func newSource(fname string, r io.RuneReader) (s source) {
s.reader = r
s.position.Filename = fname
s.position.Line = 1
s.position.Column = 1
return
}
// Source provides a stack of arune streams with position information.
type Source struct {
stack []source
tos source
}
// NewSource returns a new Source from a RuneReader having fname.
// The RuneReader can be nil. Then an EOFReader is supplied and
// the real RuneReader(s) can be Included anytime afterwards.
func NewSource(fname string, r io.RuneReader) *Source {
s := &Source{}
if r == nil {
r = EOFReader(0)
}
s.tos = newSource(fname, r)
return s
}
// Include includes a RuneReader having fname. Recursive including is not checked.
func (s *Source) Include(fname string, r io.RuneReader) {
s.stack = append(s.stack, s.tos)
s.tos = newSource(fname, r)
}
// Position return the position of the next Read.
func (s *Source) Position() token.Position {
return s.tos.position
}
// Read returns the next Source ScannerRune.
func (s *Source) Read() (r ScannerRune) {
for {
r.Position = s.Position()
r.Rune, r.Size, r.Err = s.tos.reader.ReadRune()
if r.Err == nil || r.Err != io.EOF {
p := &s.tos.position
p.Offset += r.Size
if r.Rune != '\n' {
p.Column++
} else {
p.Line++
p.Column = 1
}
return
}
// err == os.EOF, try parent source
if sp := len(s.stack) - 1; sp >= 0 {
s.tos = s.stack[sp]
s.stack = s.stack[:sp]
} else {
r.Rune, r.Size = 0, 0
return
}
}
panic("unreachable")
}
// ScannerRune is a struct holding info about a arune and its origin
type ScannerRune struct {
Position token.Position // Starting position of Rune
Rune rune // Rune value
Size int // Rune size
Err error // os.EOF or nil. Any other value invalidates all other fields of a ScannerRune.
}
// ScannerSource is a Source with one ScannerRune look behind and an on demand one ScannerRune lookahead.
type ScannerSource struct {
source *Source
prev ScannerRune
current ScannerRune
next ScannerRune
arunes []rune
}
// Accept checks if arune matches Current. If true then does Move.
func (s *ScannerSource) Accept(arune rune) bool {
if arune == s.Current() {
s.Move()
return true
}
return false
}
// NewScannerSource returns a new ScannerSource from a RuneReader having fname.
// The RuneReader can be nil. Then an EOFReader is supplied and
// the real RuneReader(s) can be Included anytime afterwards.
func NewScannerSource(fname string, r io.RuneReader) *ScannerSource {
s := &ScannerSource{}
s.source = NewSource(fname, r)
s.Move()
return s
}
// Collect returns all arunes seen by the ScannerSource since last Collect or CollectString.
// Either Collect or CollectString can be called but only one of them as both clears the collector.
func (s *ScannerSource) Collect() (arunes []rune) {
arunes, s.arunes = s.arunes, nil
return
}
// CollectString returns all arunes seen by the ScannerSource since last CollectString or Collect as a string.
// Either Collect or CollectString can be called but only one of them as both clears the collector.
func (s *ScannerSource) CollectString() string {
return string(s.Collect())
}
// CurrentRune returns the current ScannerSource arune. At EOF it's zero.
func (s *ScannerSource) Current() rune {
return s.current.Rune
}
// Current returns the current ScannerSource ScannerRune.
func (s *ScannerSource) CurrentRune() ScannerRune {
return s.current
}
// Include includes a RuneReader having fname. Recursive including is not checked.
// Include discards the one arune lookahead data if there are any.
// Lookahead data exists iff Next() has been called and Move() has not yet been called afterwards.
func (s *ScannerSource) Include(fname string, r io.RuneReader) {
s.invalidateNext()
s.arunes = nil
s.source.Include(fname, r)
s.Move()
}
func (s *ScannerSource) invalidateNext() {
s.next.Position.Line = 0
}
func (s *ScannerSource) lookahead() {
if !s.next.Position.IsValid() {
s.read(&s.next)
}
}
// Move moves ScannerSource one arune ahead.
func (s *ScannerSource) Move() {
if arune := s.Current(); arune != 0 { // collect
s.arunes = append(s.arunes, arune)
}
s.prev = s.current
if s.next.Position.IsValid() {
s.current = s.next
s.invalidateNext()
return
} else {
s.read(&s.current)
}
}
// Next returns ScannerSource next (lookahead) ScannerRune. It's Rune is zero if next is EOF.
func (s *ScannerSource) NextRune() ScannerRune {
s.lookahead()
return s.next
}
// NextRune returns ScannerSource next (lookahead) arune. It is zero if next is EOF
func (s *ScannerSource) Next() rune {
s.lookahead()
return s.next.Rune
}
// Position returns the current ScannerSource position, i.e. after a Move() it returns the position after CurrentRune.
func (s *ScannerSource) Position() token.Position {
return s.source.Position()
}
// Prev returns then previous (look behind) ScanerRune. Before first Move() its Rune is zero and Position.IsValid == false
func (s *ScannerSource) PrevRune() ScannerRune {
return s.prev
}
// PrevRune returns the previous (look behind) ScannerRune arune. Before first Move() its zero.
func (s *ScannerSource) Prev() rune {
return s.prev.Rune
}
func (s *ScannerSource) read(dest *ScannerRune) {
*dest = s.source.Read()
}