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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ebnf
import (
"container/vector";
"fmt";
"go/scanner";
"go/token";
"os";
"strconv";
"strings";
"unicode";
"utf8";
)
type parser struct {
scanner.ErrorVector;
scanner scanner.Scanner;
pos token.Position; // token position
tok token.Token; // one token look-ahead
lit []byte; // token literal
}
func (p *parser) next() {
p.pos, p.tok, p.lit = p.scanner.Scan();
if p.tok.IsKeyword() {
// TODO Should keyword mapping always happen outside scanner?
// Or should there be a flag to scanner to enable keyword mapping?
p.tok = token.IDENT;
}
}
func (p *parser) errorExpected(pos token.Position, msg string) {
msg = "expected " + msg;
if pos.Offset == p.pos.Offset {
// the error happened at the current position;
// make the error message more specific
msg += ", found '" + p.tok.String() + "'";
if p.tok.IsLiteral() {
msg += " " + string(p.lit);
}
}
p.Error(pos, msg);
}
func (p *parser) expect(tok token.Token) token.Position {
pos := p.pos;
if p.tok != tok {
p.errorExpected(pos, "'" + tok.String() + "'");
}
p.next(); // make progress in any case
return pos;
}
func (p *parser) parseIdentifier() *Name {
pos := p.pos;
name := string(p.lit);
p.expect(token.IDENT);
return &Name{pos, name};
}
func (p *parser) parseToken() *Token {
pos := p.pos;
value := "";
if p.tok == token.STRING {
value, _ = strconv.Unquote(string(p.lit));
// Unquote may fail with an error, but only if the scanner found
// an illegal string in the first place. In this case the error
// has already been reported.
p.next();
} else {
p.expect(token.STRING);
}
return &Token{pos, value};
}
func (p *parser) parseTerm() (x Expression) {
pos := p.pos;
switch p.tok {
case token.IDENT:
x = p.parseIdentifier();
case token.STRING:
tok := p.parseToken();
x = tok;
if p.tok == token.ELLIPSIS {
p.next();
x = &Range{tok, p.parseToken()};
}
case token.LPAREN:
p.next();
x = &Group{pos, p.parseExpression()};
p.expect(token.RPAREN);
case token.LBRACK:
p.next();
x = &Option{pos, p.parseExpression()};
p.expect(token.RBRACK);
case token.LBRACE:
p.next();
x = &Repetition{pos, p.parseExpression()};
p.expect(token.RBRACE);
}
return x;
}
func (p *parser) parseSequence() Expression {
var list vector.Vector;
list.Init(0);
for x := p.parseTerm(); x != nil; x = p.parseTerm() {
list.Push(x);
}
// no need for a sequence if list.Len() < 2
switch list.Len() {
case 0:
return nil;
case 1:
return list.At(0).(Expression);
}
// convert list into a sequence
seq := make(Sequence, list.Len());
for i := 0; i < list.Len(); i++ {
seq[i] = list.At(i).(Expression);
}
return seq;
}
func (p *parser) parseExpression() Expression {
var list vector.Vector;
list.Init(0);
for {
x := p.parseSequence();
if x != nil {
list.Push(x);
}
if p.tok != token.OR {
break;
}
p.next();
}
// no need for an Alternative node if list.Len() < 2
switch list.Len() {
case 0:
return nil;
case 1:
return list.At(0).(Expression);
}
// convert list into an Alternative node
alt := make(Alternative, list.Len());
for i := 0; i < list.Len(); i++ {
alt[i] = list.At(i).(Expression);
}
return alt;
}
func (p *parser) parseProduction() *Production {
name := p.parseIdentifier();
p.expect(token.ASSIGN);
expr := p.parseExpression();
p.expect(token.PERIOD);
return &Production{name, expr};
}
func (p *parser) parse(filename string, src []byte) Grammar {
// initialize parser
p.ErrorVector.Init();
p.scanner.Init(filename, src, p, 0);
p.next(); // initializes pos, tok, lit
grammar := make(Grammar);
for p.tok != token.EOF {
prod := p.parseProduction();
name := prod.Name.String;
if prev, found := grammar[name]; !found {
grammar[name] = prod;
} else {
p.Error(prod.Pos(), name + " declared already");
}
}
return grammar;
}
// Parse parses a set of EBNF productions from source src.
// It returns a set of productions. Errors are reported
// for incorrect syntax and if a production is declared
// more than once.
//
func Parse(filename string, src []byte) (Grammar, os.Error) {
var p parser;
grammar := p.parse(filename, src);
return grammar, p.GetError(scanner.Sorted);
}
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