func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.GenDecl {
	if p.trace {
		defer un(trace(p, keyword.String()+"Decl"))
	}

	doc := p.leadComment
	pos := p.expect(keyword)
	var lparen, rparen token.Position
	var list vector.Vector
	if p.tok == token.LPAREN {
		lparen = p.pos
		p.next()
		for p.tok != token.RPAREN && p.tok != token.EOF {
			list.Push(f(p, p.leadComment))
		}
		rparen = p.expect(token.RPAREN)
		p.expectSemi()
	} else {
		list.Push(f(p, nil))
	}

	// convert vector
	specs := make([]ast.Spec, len(list))
	for i, x := range list {
		specs[i] = x.(ast.Spec)
	}

	return &ast.GenDecl{doc, pos, keyword, lparen, specs, rparen}
}

func (p *Temple) addToken(tok token.Token, lit string) {
	if len(lit) > 0 {
		p.prnt.addData(" " + lit)
	} else {
		p.prnt.addData(" " + tok.String())
	}
}

// intersperseComments consumes all comments that appear before the next token
// tok and prints it together with the buffered whitespace (i.e., the whitespace
// that needs to be written before the next token). A heuristic is used to mix
// the comments and whitespace. intersperseComments returns true if a pending
// formfeed was dropped from the whitespace buffer.
//
func (p *printer) intersperseComments(next token.Position, tok token.Token) (droppedFF bool) {
	var last *ast.Comment
	for ; p.commentBefore(next); p.cindex++ {
		for _, c := range p.comments[p.cindex].List {
			p.writeCommentPrefix(p.fset.Position(c.Pos()), next, last, tok.IsKeyword())
			p.writeComment(c)
			last = c
		}
	}

	if last != nil {
		if last.Text[1] == '*' && p.fset.Position(last.Pos()).Line == next.Line {
			// the last comment is a /*-style comment and the next item
			// follows on the same line: separate with an extra blank
			p.write([]byte{' '})
		}
		// ensure that there is a line break after a //-style comment,
		// before a closing '}' unless explicitly disabled, or at eof
		needsLinebreak :=
			last.Text[1] == '/' ||
				tok == token.RBRACE && p.mode&noExtraLinebreak == 0 ||
				tok == token.EOF
		return p.writeCommentSuffix(needsLinebreak)
	}

	// no comment was written - we should never reach here since
	// intersperseComments should not be called in that case
	p.internalError("intersperseComments called without pending comments")
	return false
}

// emitArith emits to f code to compute the binary operation op(x, y)
// where op is an eager shift, logical or arithmetic operation.
// (Use emitCompare() for comparisons and Builder.logicalBinop() for
// non-eager operations.)
//
func emitArith(f *Function, op token.Token, x, y Value, t types.Type, pos token.Pos) Value {
	switch op {
	case token.SHL, token.SHR:
		x = emitConv(f, x, t)
		// y may be signed or an 'untyped' constant.
		// TODO(adonovan): whence signed values?
		if b, ok := y.Type().Underlying().(*types.Basic); ok && b.Info()&types.IsUnsigned == 0 {
			y = emitConv(f, y, types.Typ[types.Uint64])
		}

	case token.ADD, token.SUB, token.MUL, token.QUO, token.REM, token.AND, token.OR, token.XOR, token.AND_NOT:
		x = emitConv(f, x, t)
		y = emitConv(f, y, t)

	default:
		panic("illegal op in emitArith: " + op.String())

	}
	v := &BinOp{
		Op: op,
		X:  x,
		Y:  y,
	}
	v.setPos(pos)
	v.setType(t)
	return f.emit(v)
}

// intersperseComments consumes all comments that appear before the next token
// tok and prints it together with the buffered whitespace (i.e., the whitespace
// that needs to be written before the next token). A heuristic is used to mix
// the comments and whitespace. intersperseComments returns true if a pending
// formfeed was dropped from the whitespace buffer.
//
func (p *printer) intersperseComments(next token.Position, tok token.Token) (droppedFF bool) {
	var last *ast.Comment
	for ; p.commentBefore(next); p.cindex++ {
		for _, c := range p.comments[p.cindex].List {
			p.writeCommentPrefix(c.Pos(), next, last == nil, tok.IsKeyword())
			p.writeComment(c)
			last = c
		}
	}

	if last != nil {
		if last.Text[1] == '*' && last.Pos().Line == next.Line {
			// the last comment is a /*-style comment and the next item
			// follows on the same line: separate with an extra blank
			p.write([]byte{' '})
		}
		// ensure that there is a newline after a //-style comment
		// or if we are before a closing '}' or at the end of a file
		return p.writeCommentSuffix(last.Text[1] == '/' || tok == token.RBRACE || tok == token.EOF)
	}

	// no comment was written - we should never reach here since
	// intersperseComments should not be called in that case
	p.internalError("intersperseComments called without pending comments")
	return false
}

// intersperseComments consumes all comments that appear before the next token
// tok and prints it together with the buffered whitespace (i.e., the whitespace
// that needs to be written before the next token). A heuristic is used to mix
// the comments and whitespace. The intersperseComments result indicates if a
// newline was written or if a formfeed was dropped from the whitespace buffer.
//
func (p *printer) intersperseComments(next token.Position, tok token.Token) (wroteNewline, droppedFF bool) {
	var last *ast.Comment
	for p.commentBefore(next) {
		for _, c := range p.comment.List {
			p.writeCommentPrefix(p.posFor(c.Pos()), next, last, c, tok.IsKeyword())
			p.writeComment(c)
			last = c
		}
		p.nextComment()
	}

	if last != nil {
		// if the last comment is a /*-style comment and the next item
		// follows on the same line but is not a comma or a "closing"
		// token, add an extra blank for separation
		if last.Text[1] == '*' && p.lineFor(last.Pos()) == next.Line && tok != token.COMMA &&
			tok != token.RPAREN && tok != token.RBRACK && tok != token.RBRACE {
			p.writeByte(' ', 1)
		}
		// ensure that there is a line break after a //-style comment,
		// before a closing '}' unless explicitly disabled, or at eof
		needsLinebreak :=
			last.Text[1] == '/' ||
				tok == token.RBRACE && p.mode&noExtraLinebreak == 0 ||
				tok == token.EOF
		return p.writeCommentSuffix(needsLinebreak)
	}

	// no comment was written - we should never reach here since
	// intersperseComments should not be called in that case
	p.internalError("intersperseComments called without pending comments")
	return
}

func (p *parser) expect(tok token.Token) token.Pos {
	pos := p.pos
	if p.tok != tok {
		p.errorExpected(pos, "'"+tok.String()+"'")
	}
	p.next() // make progress in any case
	return pos
}

// kindToType transforms Go token kind to type name.
func kindToType(kind token.Token) string {
	switch kind.String() {
	case "STRING":
		return "string"
	case "INT":
		return "int"
	default:
		return ""
	}
}

// Comapres xv to yv using operator op
// Both xv and yv must be loaded and have a compatible type (as determined by negotiateType)
func compareOp(op token.Token, xv *Variable, yv *Variable) (bool, error) {
	switch xv.Kind {
	case reflect.Bool:
		fallthrough
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		fallthrough
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		fallthrough
	case reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
		return constantCompare(op, xv.Value, yv.Value)
	case reflect.String:
		if int64(len(constant.StringVal(xv.Value))) != xv.Len || int64(len(constant.StringVal(yv.Value))) != yv.Len {
			return false, fmt.Errorf("string too long for comparison")
		}
		return constantCompare(op, xv.Value, yv.Value)
	}

	if op != token.EQL && op != token.NEQ {
		return false, fmt.Errorf("operator %s not defined on %s", op.String(), xv.Kind.String())
	}

	var eql bool
	var err error

	switch xv.Kind {
	case reflect.Ptr:
		eql = xv.Children[0].Addr == yv.Children[0].Addr
	case reflect.Array:
		if int64(len(xv.Children)) != xv.Len || int64(len(yv.Children)) != yv.Len {
			return false, fmt.Errorf("array too long for comparison")
		}
		eql, err = equalChildren(xv, yv, true)
	case reflect.Struct:
		if len(xv.Children) != len(yv.Children) {
			return false, nil
		}
		if int64(len(xv.Children)) != xv.Len || int64(len(yv.Children)) != yv.Len {
			return false, fmt.Errorf("sturcture too deep for comparison")
		}
		eql, err = equalChildren(xv, yv, false)
	case reflect.Slice, reflect.Map, reflect.Func, reflect.Chan:
		if xv != nilVariable && yv != nilVariable {
			return false, fmt.Errorf("can not compare %s variables", xv.Kind.String())
		}

		eql = xv.base == yv.base
	default:
		return false, fmt.Errorf("unimplemented comparison of %s variables", xv.Kind.String())
	}

	if op == token.NEQ {
		return !eql, err
	}
	return eql, err
}

func negotiateTypeNil(op token.Token, v *Variable) error {
	if op != token.EQL && op != token.NEQ {
		return fmt.Errorf("operator %s can not be applied to \"nil\"", op.String())
	}
	switch v.Kind {
	case reflect.Ptr, reflect.UnsafePointer, reflect.Chan, reflect.Map, reflect.Interface, reflect.Slice, reflect.Func:
		return nil
	default:
		return fmt.Errorf("can not compare %s to nil", v.Kind.String())
	}
}

func evalUnaryBoolExpr(ctx *Ctx, x reflect.Value, op token.Token) (reflect.Value, error) {
	var err error
	var r bool

	xx := x.Bool()
	switch op {
	case token.NOT:
		r = !xx
	default:
		panic("eval: impossible unary op " + op.String())
	}
	return reflect.ValueOf(r).Convert(x.Type()), err
}

func evalUnaryFloatExpr(ctx *Ctx, x reflect.Value, op token.Token) (reflect.Value, error) {
	var err error
	var r float64

	xx := x.Float()
	switch op {
	case token.ADD:
		r = +xx
	case token.SUB:
		r = -xx
	default:
		panic("eval: impossible unary op " + op.String())
	}
	return reflect.ValueOf(r).Convert(x.Type()), err
}

// TokenKind returns a syntaxhighlight token kind value for the given tok and lit.
func TokenKind(tok token.Token, lit string) syntaxhighlight.Kind {
	switch {
	case tok.IsKeyword() || (tok.IsOperator() && tok <= token.ELLIPSIS):
		return syntaxhighlight.Keyword

	// Literals.
	case tok == token.INT || tok == token.FLOAT || tok == token.IMAG || tok == token.CHAR:
		return syntaxhighlight.Decimal
	case tok == token.STRING:
		return syntaxhighlight.String
	case lit == "true" || lit == "false" || lit == "iota" || lit == "nil":
		return syntaxhighlight.Literal

	case tok == token.COMMENT:
		return syntaxhighlight.Comment
	default:
		return syntaxhighlight.Plaintext
	}
}

func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction, getSemi bool) (decl *ast.GenDecl, gotSemi bool) {
	if p.trace {
		defer un(trace(p, keyword.String()+"Decl"))
	}

	doc := p.leadComment
	pos := p.expect(keyword)
	var lparen, rparen token.Position
	list := new(vector.Vector)
	if p.tok == token.LPAREN {
		lparen = p.pos
		p.next()
		for p.tok != token.RPAREN && p.tok != token.EOF {
			doc := p.leadComment
			spec, semi := f(p, doc, true) // consume semicolon if any
			list.Push(spec)
			if !semi {
				break
			}
		}
		rparen = p.expect(token.RPAREN)

		if getSemi && p.tok == token.SEMICOLON {
			p.next()
			gotSemi = true
		} else {
			p.optSemi = true
		}
	} else {
		spec, semi := f(p, nil, getSemi)
		list.Push(spec)
		gotSemi = semi
	}

	// convert vector
	specs := make([]ast.Spec, list.Len())
	for i := 0; i < list.Len(); i++ {
		specs[i] = list.At(i).(ast.Spec)
	}

	return &ast.GenDecl{doc, pos, keyword, lparen, specs, rparen}, gotSemi
}

// emitArith emits to f code to compute the binary operation op(x, y)
// where op is an eager shift, logical or arithmetic operation.
// (Use emitCompare() for comparisons and Builder.logicalBinop() for
// non-eager operations.)
//
func emitArith(f *Function, op token.Token, x, y Value, t types.Type) Value {
	switch op {
	case token.SHL, token.SHR:
		x = emitConv(f, x, t)
		y = emitConv(f, y, types.Typ[types.Uint64])

	case token.ADD, token.SUB, token.MUL, token.QUO, token.REM, token.AND, token.OR, token.XOR, token.AND_NOT:
		x = emitConv(f, x, t)
		y = emitConv(f, y, t)

	default:
		panic("illegal op in emitArith: " + op.String())

	}
	v := &BinOp{
		Op: op,
		X:  x,
		Y:  y,
	}
	v.setType(t)
	return f.emit(v)
}

func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.GenDecl {
	if p.trace {
		defer un(trace(p, "GenDecl("+keyword.String()+")"))
	}

	doc := p.leadComment
	pos := p.expect(keyword)
	var lparen, rparen token.Pos
	var list []ast.Spec
	if p.tok == token.LPAREN {
		lparen = p.pos
		p.next()
		for p.tok != token.RPAREN && p.tok != token.EOF {
			list = append(list, f(p, p.leadComment))
		}
		rparen = p.expect(token.RPAREN)
		p.expectSemi()
	} else {
		list = append(list, f(p, nil))
	}

	return &ast.GenDecl{doc, pos, keyword, lparen, list, rparen}
}

func tokenclass(tok token.Token) int {
	switch {
	case tok.IsLiteral():
		return literal
	case tok.IsOperator():
		return operator
	case tok.IsKeyword():
		return keyword
	}
	return special
}

func (self *HTMLStyler) Token(tok token.Token) ([]byte, printer.HTMLTag) {
	extra := ""

	if tok.IsKeyword() {
		extra += " go-keyword"
	}

	if tok.IsLiteral() {
		extra += " go-literal"
	}

	if tok.IsOperator() {
		extra += " go-operator"
	}

	self.prev = tok

	return []byte(tok.String()), printer.HTMLTag{
		Start: "<span class=\"go-token" + extra + "\">",
		End:   "</span>",
	}
}

func getColor(tok token.Token) string {
	switch {
	case tok.IsKeyword():
		return Colors[Keyword]
	case tok.IsLiteral():
		if tok == token.IDENT {
			return Colors[Identifier]
		} else {
			return Colors[Literal]
		}
	case tok.IsOperator():
		return Colors[Operator]
	case tok == token.COMMENT:
		return Colors[Comment]
	case tok == token.ILLEGAL:
		return Colors[Illegal]
	default:
		panic(fmt.Sprintf("unknown token type: %v", tok))
	}
	return ""
}

// getClass returns the CSS class name associated with tok.
func (h *Highlighter) getClass(tok token.Token) string {
	switch {
	case tok.IsKeyword():
		return h.KeywordClass
	case tok.IsLiteral():
		if tok == token.IDENT {
			return h.IdentClass
		} else {
			return h.LiteralClass
		}
	case tok.IsOperator():
		return h.OperatorClass
	case tok == token.COMMENT:
		return h.CommentClass
	case tok == token.ILLEGAL:
		break
	default:
		panic(fmt.Sprintf("unknown token type: %v", tok))
	}
	return ""
}