// 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 main // This file contains the mechanism to "linkify" html source // text containing EBNF sections (as found in go_spec.html). // The result is the input source text with the EBNF sections // modified such that identifiers are linked to the respective // definitions. import ( "bytes" "fmt" "io" "text/scanner" ) type ebnfParser struct { out io.Writer // parser output src []byte // parser input scanner scanner.Scanner prev int // offset of previous token pos int // offset of current token tok rune // one token look-ahead lit string // token literal } func (p *ebnfParser) flush() { p.out.Write(p.src[p.prev:p.pos]) p.prev = p.pos } func (p *ebnfParser) next() { p.tok = p.scanner.Scan() p.pos = p.scanner.Position.Offset p.lit = p.scanner.TokenText() } func (p *ebnfParser) printf(format string, args ...interface{}) { p.flush() fmt.Fprintf(p.out, format, args...) } func (p *ebnfParser) errorExpected(msg string) { p.printf(`error: expected %s, found %s`, msg, scanner.TokenString(p.tok)) } func (p *ebnfParser) expect(tok rune) { if p.tok != tok { p.errorExpected(scanner.TokenString(tok)) } p.next() // make progress in any case } func (p *ebnfParser) parseIdentifier(def bool) { if p.tok == scanner.Ident { name := p.lit if def { p.printf(`%s`, name, name) } else { p.printf(`%s`, name, name) } p.prev += len(name) // skip identifier when printing next time p.next() } else { p.expect(scanner.Ident) } } func (p *ebnfParser) parseTerm() bool { switch p.tok { case scanner.Ident: p.parseIdentifier(false) case scanner.String: p.next() const ellipsis = '…' // U+2026, the horizontal ellipsis character if p.tok == ellipsis { p.next() p.expect(scanner.String) } case '(': p.next() p.parseExpression() p.expect(')') case '[': p.next() p.parseExpression() p.expect(']') case '{': p.next() p.parseExpression() p.expect('}') default: return false // no term found } return true } func (p *ebnfParser) parseSequence() { if !p.parseTerm() { p.errorExpected("term") } for p.parseTerm() { } } func (p *ebnfParser) parseExpression() { for { p.parseSequence() if p.tok != '|' { break } p.next() } } func (p *ebnfParser) parseProduction() { p.parseIdentifier(true) p.expect('=') if p.tok != '.' { p.parseExpression() } p.expect('.') } func (p *ebnfParser) parse(out io.Writer, src []byte) { // initialize ebnfParser p.out = out p.src = src p.scanner.Init(bytes.NewBuffer(src)) p.next() // initializes pos, tok, lit // process source for p.tok != scanner.EOF { p.parseProduction() } p.flush() } // Markers around EBNF sections var ( openTag = []byte(`
`)
	closeTag = []byte(`
`) ) func Linkify(out io.Writer, src []byte) { for len(src) > 0 { // i: beginning of EBNF text (or end of source) i := bytes.Index(src, openTag) if i < 0 { i = len(src) - len(openTag) } i += len(openTag) // j: end of EBNF text (or end of source) j := bytes.Index(src[i:], closeTag) // close marker if j < 0 { j = len(src) - i } j += i // write text before EBNF out.Write(src[0:i]) // process EBNF var p ebnfParser p.parse(out, src[i:j]) // advance src = src[j:] } }