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parser.go
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/
parser.go
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// Copyright (C) 2015 A.Newman
//
package main
import (
"errors"
"fmt"
"io"
)
var (
errSyntax = errors.New("Syntax error")
)
type Parser struct {
l *Lexer
Current Token
Text string
Err error
}
func NewParser(r io.Reader) *Parser {
p := &Parser{l: NewLexer(r)}
p.Advance()
return p
}
func (p *Parser) SetError(err error) {
if p.Err == nil {
p.Err = err
}
}
func (p *Parser) Broken() bool {
return p.Err != nil
}
func (p *Parser) Advance() {
if !p.Broken() {
p.Current, p.Text, p.Err = p.l.Get()
}
}
func (p *Parser) Done() bool {
return p.Current == TokEOF || p.Broken()
}
func (p *Parser) Match(t Token) (string, bool) {
if p.Broken() {
return "", false
}
matched := t == p.Current
text := ""
if matched {
text = p.Text
p.Advance()
}
return text, matched
}
func (p *Parser) MatchOneOf(tokens []Token) (Token, bool) {
if p.Broken() {
return TokEOF, false
}
matched := false
tok := TokEOF
for _, token := range tokens {
if p.Current == token {
matched = true
tok = token
break
}
}
if matched {
p.Advance()
}
return tok, matched
}
func (p *Parser) MustMatch(t Token) (text string, matched bool) {
if text, matched = p.Match(t); !matched {
p.SetError(p.Expected(t, text))
}
return
}
func (p *Parser) Expected(t Token, text string) error {
return fmt.Errorf("%d: expected %s, got %s %q", p.l.Line, t, p.Current, text)
}
func (p *Parser) Syntax(msg string) error {
return fmt.Errorf("syntax error: %s", msg)
}