/
stream.go
119 lines (107 loc) · 2.17 KB
/
stream.go
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// Copyright (C) 2017 JT Olds
// See LICENSE for copying information.
package sheepda
import (
"bufio"
"fmt"
"io"
"unicode"
)
// Stream makes parsing a sequence of runes easier
type Stream struct {
data *bufio.Reader
next *rune
err error
}
// NewStream creates a new stream from an io.Reader
func NewStream(in io.Reader) *Stream {
return &Stream{data: bufio.NewReader(in)}
}
// EOF returns if the stream has ended.
func (s *Stream) EOF() bool { return s.err == io.EOF }
func (s *Stream) readRune() (rune, error) {
r, _, err := s.data.ReadRune()
if err != nil {
return 0, err
}
if r == unicode.ReplacementChar {
return 0, fmt.Errorf("invalid unicode")
}
return r, nil
}
func (s *Stream) fillNext() error {
if s.next != nil {
return nil
}
if s.err != nil {
return s.err
}
r, err := s.readRune()
if err != nil {
s.err = err
return err
}
if r == '#' {
for {
r, err := s.readRune()
if err != nil {
s.err = err
return err
}
if r == '\n' {
break
}
}
return s.fillNext()
}
s.next = &r
return nil
}
// Peek returns the next rune but does not pop it out of the stream.
func (s *Stream) Peek() (rune, error) {
err := s.fillNext()
if err != nil {
return 0, err
}
return *s.next, nil
}
// Next pops any current rune out of the stream. It won't advance the stream
// farther though.
func (s *Stream) Next() {
s.next = nil
}
// Get will advance the stream and return the next rune.
func (s *Stream) Get() (r rune, err error) {
r, err = s.Peek()
s.Next()
return r, err
}
// SwallowWhitespace will advance the stream past any whitespace.
func (s *Stream) SwallowWhitespace() error {
for {
r, err := s.Peek()
if err != nil {
if err == io.EOF {
return nil
}
return err
}
if !unicode.IsSpace(r) {
return nil
}
s.Next()
}
}
// AssertMatch will make sure the current rune is in the set of possible
// options and error otherwise. Then it will swallow any whitespace.
func (s *Stream) AssertMatch(options map[rune]bool) error {
r, err := s.Get()
if err != nil {
return err
}
if !options[r] {
return fmt.Errorf("unexpected rune. expected %#v, got %#v",
options, string(r))
}
return s.SwallowWhitespace()
}