weekly snapshot:

- template-driven ast printing now can successfully
  reproduce entire Go programs

next steps:
- fine-tuning of output
- print interspersed comments
- cleanup and testing against all Go programs
- replace astprinter

R=r
OCL=28181
CL=28181

4 files changed, 573 insertions, 265 deletions

diff --git a/usr/gri/pretty/ast.txt b/usr/gri/pretty/ast.txt
index fbf1fdc9e..d25a5a3bf 100644
--- a/usr/gri/pretty/ast.txt
+++ b/usr/gri/pretty/ast.txt
@@ -2,216 +2,314 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Format file for printing AST nodes (package "ast").
+
 // ----------------------------------------------------------------------------
 // Debugging
 
 token.Token =
-	^ : "%s";
+	^:string;
 
+array =
+	*;
+
+pointer =
+	*;
+
+string =
+	"%s";
+
+char =
+	"%c";
+
+bytes =
+	{*};
+
+nil =
+	;  // TODO we see a lot of nil's - why?
+
+not_empty =
+	*:nil;
 
-// Format file for printing AST nodes (package "ast").
-ast;
 
 // ----------------------------------------------------------------------------
-// TODO should these be automatic?
+// TODO these are implicit - only here for debugging
 
-Expr =
-	"expr ";
-	//*;
+ast.Expr =
+	*;
 
-Stmt =
+ast.Stmt =
 	*;
 
-Decl =
+ast.Decl =
 	*;
 
+
 // ----------------------------------------------------------------------------
 // Comments
 
-Comment =
-	Text : "%s\n";
+ast.Comment =
+	Text:string "\n";
 
-Comments =
+ast.Comments =
 	{*};
 
 
 // ----------------------------------------------------------------------------
 // Expressions & Types
 
-Field =
-	{Names ", "} Type;
+ast.Field =
+	[Names:not_empty {Names / ", "} " "] Type;
 
-BadExpr =
+ast.BadExpr =
 	"BAD EXPR";
 
-Ident =
+ast.Ident =
 	Value;
 
-Elipsis =
+ast.Ellipsis =
 	"...";
 
-IntLit =
-	Value : "%s";
+ast.IntLit =
+	Value:string;
 
-FloatLit =
-	Value : "%s";
+ast.FloatLit =
+	Value:string;
 
-CharLit =
-	Value : "%s";
+ast.CharLit =
+	Value:string;
 
-StringLit =
-	Value : "%s";
+ast.StringLit =
+	Value:string;
 
-StringList =
-	{ Strings };
+ast.StringList =
+	{Strings / "\n"};
 
-FuncLit =
+ast.FuncLit =
 	"func ";
 
-CompositeLit =
-	Type "{}";
+ast.CompositeLit =
+	Type "{" {Elts / ", "} "}";
 
-ParenExpr =
+ast.ParenExpr =
 	"(" X ")";
 
-SelectorExpr =
+ast.SelectorExpr =
 	X "." Sel;
 
-IndexExpr =
+ast.IndexExpr =
 	X "[" Index "]";
 
-SliceExpr =
-	X "[" Begin " : " End "]";
+ast.SliceExpr =
+	X "[" Begin ":" End "]";
 
-TypeAssertExpr =
+ast.TypeAssertExpr =
 	X ".(" Type ")";
 
-CallExpr =
-	Fun "(" {Args} ")";
+ast.CallExpr =
+	Fun "(" {Args / ", "} ")";
 
-StarExpr =
+ast.StarExpr =
 	"*" X;
 
-UnaryExpr =
+ast.UnaryExpr =
 	Op X;
 
-BinaryExpr =
-	X Op Y;
+ast.BinaryExpr =
+	X " " Op " " Y;
 
-KeyValueExpr =
+ast.KeyValueExpr =
 	Key ": " Value;
 
-ArrayType =
+ast.ArrayType =
 	"[" Len "]" Elt;
 
-SliceType =
+ast.SliceType =
 	"[]" Elt;
 
-StructType =
-	"struct {\n"
+ast.StructType =
+	"struct {"
+	[Fields:not_empty
+	>> "\t" "\n"
+		{Fields / ";\n"}
+	<< "\n"
+	]
 	"}";
 
-FuncType =
-	"(" {Params " "} ")";
+signature =
+	"(" {Params / ", "} ")" [Results:not_empty " (" {Results / ", "} ")"];
+
+funcSignature =
+	*:signature;
+
+ast.FuncType =
+	"func" ^:signature;
 
-// BUG take this one away and the code crashes
-InterfaceType =
-	"interface {}";
+ast.InterfaceType =
+	"interface {"
+	[Methods:not_empty
+	>> "\t" "\n"
+		{Methods / ";\n"}  // TODO should not start with "func"
+	<< "\n"
+	]
+	"}";
 
-MapType =
+ast.MapType =
 	"map[" Key "]" Value;
 
-ChanType =
+ast.ChanType =
 	"chan";
 
 
 // ----------------------------------------------------------------------------
 // Statements
 
-BadStmt =
+ast.BadStmt =
 	"BAD STMT";
 
-DeclStmt =
+ast.DeclStmt =
 	Decl;
 
-EmptyStmt =
+ast.EmptyStmt =
 	;
 
-LabeledStmt =
+ast.LabeledStmt =
 	Label ":\t" Stmt;
 
-ExprStmt =
+ast.ExprStmt =
 	X;
 
-IncDecStmt =
+ast.IncDecStmt =
 	X Tok;
 
-AssignStmt =
-	"assignment " {Lhs ", "};
-	//{Lhs ", "} Tok {Rhs ", "};
+ast.AssignStmt =
+	{Lhs / ", "} " " Tok " " {Rhs / ", "};
 
-GoStmt =
+ast.GoStmt =
 	"go " Call;
 
-ReturnStmt =
-	"return" {" " Results};
+ast.ReturnStmt =
+	"return" {" " Results / ","};
 
-BranchStmt =
+ast.BranchStmt =
 	Tok [" " Label];
 
-BlockStmt =
-	"{\n" {List ";\n"} "}\n";
-
-IfStmt =
-	"if " "{" [Body] "}" [Else];
-
-SwitchStmt =
-	"switch {}";
-
-TypeSwitchStmt =
-	"switch {}";
+blockStmt =  // like ast.BlockStmt but w/o indentation
+	"{"
+	[List:not_empty
+	"\n"
+		{List / ";\n"}
+	"\n"
+	]
+	"}";
 
-SelectStmt =
-	"select {}";
+blockStmtPtr =
+	*:blockStmt;
 
-ForStmt =
-	"for {}";
+ast.BlockStmt =
+	"{"
+	[List:not_empty
+	>> "\t" "\n"
+		{List / ";\n"}
+	<< "\n"
+	]
+	"}";
 
-RangeStmt =
-	"range";
+ast.IfStmt =
+	"if " [Init "; "] [Cond " "] Body [" else " Else];
+
+ast.CaseClause =
+	( Values:not_empty "case " {Values / ", "}
+	| "default"
+	)
+	":"
+	[Body:not_empty
+	>> "\t" "\n"
+		{Body / ";\n"}
+	<<
+	];
+
+ast.SwitchStmt =
+	"switch " [Init "; "] [Tag " "]
+	Body:blockStmtPtr;
+
+ast.TypeCaseClause =
+	(	Type:not_empty "case " Type
+	|	"default"
+	)
+	":"
+	[Body:not_empty
+	>> "\t" "\n"
+		{Body / ";\n"}
+	<<
+	];
+
+ast.TypeSwitchStmt =
+	"switch " Assign " "
+	Body:blockStmtPtr;
+
+ast.CommClause =
+	"CommClause";
+
+ast.SelectStmt =
+	"select "
+	Body:blockStmtPtr;
+
+ast.ForStmt =
+	"for "
+	[	Init:not_empty
+		[Init] "; " [Cond] "; " [Post " "]
+	|	Post:not_empty
+		[Init] "; " [Cond] "; " [Post " "]
+	|	Cond " "
+	]
+	Body;
+
+ast.RangeStmt =
+	"for " Key [", " Value] " " Tok " range " X
+	" "
+	Body;
 
 
 // ----------------------------------------------------------------------------
 // Declarations
 
-Spec =
+ast.Spec =
 	*;
 
-ImportSpec =
-	"import";
+ast.ImportSpec =
+	Doc
+	[Name] "\t" {Path};
 
-ValueSpec =
-	"value";
+ast.ValueSpec =
+	{Names / ", "} [" " Type] [Values:not_empty " = " {Values / ", "}];
 
-TypeSpec =
-	"type";
+ast.TypeSpec =
+	Name " "  // TODO using "\t" instead of " " screws up struct field alignment
+	Type;
 
-BadDecl =
+ast.BadDecl =
 	"BAD DECL";
 
-GenDecl =
+ast.GenDecl =
 	Doc
-	Tok " (\n"
-	")\n";
-	
-FuncDecl =
-	"func " ["(" Recv ") "] Name Type [" " Body];
-	
+	Tok " ("
+	>> "\t" "\n"
+		{Specs / ";\n"}
+	<<
+	"\n"
+	")";
+
+ast.FuncDecl =
+	"func " ["(" Recv ") "] Name Type:funcSignature
+	[" " Body]
+	"\n";
+
 
 // ----------------------------------------------------------------------------
 // Program
 
-Program =
+ast.Program =
 	Doc
 	"package " Name "\n\n"
-	{Decls "\n\n"};
+	{Decls / "\n\n"};
diff --git a/usr/gri/pretty/format.go b/usr/gri/pretty/format.go
index 62009d2c8..eff983633 100644
--- a/usr/gri/pretty/format.go
+++ b/usr/gri/pretty/format.go
@@ -32,13 +32,22 @@ import (
 )
 
 
-// TODO remove once the code works
-var debug = flag.Bool("d", false, "debug mode");
+// TODO should probably do this in a different way
+var (
+	debug = flag.Bool("d", false, "debug mode");
+	trace = flag.Bool("t", false, "trace mode");
+)
 
 
 // ----------------------------------------------------------------------------
 // Format representation
 
+type (
+	Formatter func(w io.Write, value interface{}, name string) bool;
+	FormatterMap map[string]Formatter;
+)
+
+
 // A production expression is built from the following nodes.
 //
 type (
@@ -54,28 +63,36 @@ type (
 		x, y expr;
 	};
 
-	field struct {
-		name string;  // including "^", "*"
-		fexpr expr;  // nil if no fexpr specified
-	};
-	
 	literal struct {
 		// TODO should there be other types or should it all be string literals?
 		value []byte;
 	};
 
+	indentation struct {
+		iexpr expr;  // outdent if nil
+	};
+
+	field struct {
+		fname string;  // including "^", "*"
+		tname string;  // "" if no tname specified
+	};
+
+	negation struct {
+		neg expr;
+	};
+
 	option struct {
-		x expr
+		opt expr;
 	};
 
 	repetition struct {
-		x expr
+		rep expr;
+		div expr;
 	};
 
-	// TODO custom formats are not yet used
 	custom struct {
 		name string;
-		f func(w io.Write, value interface{}, name string) bool
+		form Formatter
 	};
 )
 
@@ -90,31 +107,47 @@ func (x *sequence) String() string {
 }
 
 
+func (x *literal) String() string {
+	return strconv.Quote(string(x.value));
+}
+
+
+func (x *indentation) String() string {
+	if x.iexpr != nil {
+		fmt.Sprintf(">> %s", x.iexpr);
+	}
+	return "<<";
+}
+
+
 func (x *field) String() string {
-	if x.fexpr == nil {
-		return x.name;
+	if x.tname == "" {
+		return x.fname;
 	}
-	return fmt.Sprintf("%s: (%v)", x.name, x.fexpr);
+	return x.fname + " : " + x.tname;
 }
 
 
-func (x *literal) String() string {
-	return strconv.Quote(string(x.value));
+func (x *negation) String() string {
+	return fmt.Sprintf("!%v", x.neg);
 }
 
 
 func (x *option) String() string {
-	return fmt.Sprintf("[%v]", x.x);
+	return fmt.Sprintf("[%v]", x.opt);
 }
 
 
 func (x *repetition) String() string {
-	return fmt.Sprintf("{%v}", x.x);
+	if x.div == nil {
+		return fmt.Sprintf("{%v}", x.rep);
+	}
+	return fmt.Sprintf("{%v / %v}", x.rep, x.div);
 }
 
 
 func (x *custom) String() string {
-	return fmt.Sprintf("<custom %s>", x.name);
+	return "<" + x.name + ">";
 }
 
 
@@ -124,13 +157,15 @@ func (x *custom) String() string {
 
 	Formatting rules are specified in the following syntax:
 
-		Format      = { Production } .
-		Production  = Name [ "=" [ Expression ] ] ";" .
+		Format      = Production { ";" Production } [ ";" ] .
+		Production  = Name "=" Expression .
 		Name        = identifier { "." identifier } .
-		Expression  = Term { "|" Term } .
+		Expression  = [ Term ] { "|" [ Term ] } .
 		Term        = Factor { Factor } .
-		Factor      = string_literal | Field | Group | Option | Repetition .
-		Field       = ( "^" | "*" | Name ) [ ":" Expression ] .
+		Factor      = string_literal | Indent | Field | Negation | Group | Option | Repetition .
+		Indent      = ">>" Factor | "<<" .
+		Field       = ( "^" | "*" | Name ) [ ":" Name ] .
+		Negation    = "!" Factor .
 		Group       = "(" Expression ")" .
 		Option      = "[" Expression "]" .
 		Repetition  = "{" Expression "}" .
@@ -182,9 +217,6 @@ type Format map [string] expr;
 	- installable custom formatters (like for template.go)
 	- have a format to select type name, field tag, field offset?
 	- use field tag as default format for that field
-	- field format override (":") is not working as it should
-	  (cannot refer to another production - syntactially not possible
-	  at the moment)
 */
 
 type parser struct {
@@ -257,12 +289,6 @@ func (p *parser) parseName() string {
 }
 
 
-// TODO WriteByte should be a ByteBuffer method
-func writeByte(buf *io.ByteBuffer, b byte) {
-	buf.Write([]byte{b});
-}
-
-
 func (p *parser) parseValue() []byte {
 	if p.tok != token.STRING {
 		p.expect(token.STRING);
@@ -281,30 +307,33 @@ func (p *parser) parseValue() []byte {
 }
 
 
+func (p *parser) parseFactor() (x expr)
 func (p *parser) parseExpr() expr
 
 func (p *parser) parseField() expr {
-	var name string;
+	var fname string;
 	switch p.tok {
 	case token.XOR:
-		name = "^";
+		fname = "^";
 		p.next();
 	case token.MUL:
-		name = "*";
+		fname = "*";
 		p.next();
 	case token.IDENT:
-		name = p.parseName();
+		// TODO use reflect.ExpandType() to lookup a field
+		// during parse-time if posssible
+		fname = p.parseName();
 	default:
 		return nil;
 	}
 
-	var fexpr expr;
+	var tname string;
 	if p.tok == token.COLON {
 		p.next();
-		fexpr = p.parseExpr();
+		tname = p.parseName();
 	}
 	
-	return &field{name, fexpr};
+	return &field{fname, tname};
 }
 
 
@@ -313,6 +342,18 @@ func (p *parser) parseFactor() (x expr) {
 	case token.STRING:
 		x = &literal{p.parseValue()};
 
+	case token.SHR:
+		p.next();
+		x = &indentation{p.parseFactor()};
+
+	case token.SHL:
+		p.next();
+		x = &indentation{nil};
+
+	case token.NOT:
+		p.next();
+		x = &negation{p.parseFactor()};
+
 	case token.LPAREN:
 		p.next();
 		x = p.parseExpr();
@@ -325,7 +366,13 @@ func (p *parser) parseFactor() (x expr) {
 
 	case token.LBRACE:
 		p.next();
-		x = &repetition{p.parseExpr()};
+		x = p.parseExpr();
+		var div expr;
+		if p.tok == token.QUO {
+			p.next();
+			div = p.parseExpr();
+		}
+		x = &repetition{x, div};
 		p.expect(token.RBRACE);
 
 	default:
@@ -338,18 +385,15 @@ func (p *parser) parseFactor() (x expr) {
 
 func (p *parser) parseTerm() expr {
 	x := p.parseFactor();
-	if x == nil {
-		p.error_expected(p.pos, "factor");
-		p.next();  // make progress
-		return nil;
-	}
 
-	for {
-		y := p.parseFactor();
-		if y == nil {
-			break;
+	if x != nil {
+		for {
+			y := p.parseFactor();
+			if y == nil {
+				break;
+			}
+			x = &sequence{x, y};
 		}
-		x = &sequence{x, y};
 	}
 
 	return x;
@@ -369,36 +413,35 @@ func (p *parser) parseExpr() expr {
 }
 
 
+func (p *parser) parseProd() (string, expr) {
+	name := p.parseName();
+	p.expect(token.ASSIGN);
+	x := p.parseExpr();
+	return name, x; 
+}
+
+
 func (p *parser) parseFormat() Format {
 	format := make(Format);
 	
-	prefix := "";
 	for p.tok != token.EOF {
 		pos := p.pos;
-		name := p.parseName();
-		
-		if p.tok == token.ASSIGN {
-			// production
+		name, x := p.parseProd();
+
+		// add production to format
+		if t, found := format[name]; !found {
+			format[name] = x;
+		} else {
+			p.Error(pos, "production already declared: " + name);
+		}
+
+		if p.tok == token.SEMICOLON {
 			p.next();
-			var x expr;
-			if p.tok != token.SEMICOLON {
-				x = p.parseExpr();
-			}
-			// add production to format
-			name = prefix + name;
-			if t, found := format[name]; !found {
-				format[name] = x;
-			} else {
-				p.Error(pos, "production already declared: " + name);
-			}
-			
 		} else {
-			// prefix only
-			prefix = name + ".";
+			break;
 		}
-		
-		p.expect(token.SEMICOLON);
 	}
+	p.expect(token.EOF);
 	
 	return format;
 }
@@ -441,18 +484,36 @@ func readSource(src interface{}, err scanner.ErrorHandler) []byte {
 // a string, a []byte, or implement io.Read. The result is a Format
 // if no errors occured; otherwise Parse returns nil.
 //
-func Parse(src interface{}) Format {
+func Parse(src interface{}, fmap FormatterMap) Format {
 	// initialize parser
 	var p parser;
 	p.scanner.Init(readSource(src, &p), &p, false);
 	p.next();
 
-	f := p.parseFormat();
-
+	format := p.parseFormat();
 	if p.lastline > 0 {	
 		return nil;  // src contains errors
 	}
-	return f;
+	
+	// add custom formatters if any
+	if fmap != nil {
+		for name, form := range fmap {
+			if t, found := format[name]; !found {
+				format[name] = &custom{name, form};
+			} else {
+				p.Error(token.Position{0, 0, 0}, "formatter already declared: " + name);
+			}
+		}
+	}
+
+	return format;
+}
+
+
+func (f Format) Dump() {
+	for name, form := range f {
+		fmt.Printf("%s = %v;\n", name, form);
+	}
 }
 
 
@@ -473,10 +534,12 @@ func fieldIndex(v reflect.StructValue, fieldname string) int {
 
 func getField(v reflect.StructValue, i int) reflect.Value {
 	fld := v.Field(i);
+	/*
 	if tmp, is_interface := fld.(reflect.InterfaceValue); is_interface {
 		// TODO do I have to check something for nil here?
 		fld = reflect.NewValue(tmp.Get());
 	}
+	*/
 	return fld;
 }
 
@@ -484,7 +547,7 @@ func getField(v reflect.StructValue, i int) reflect.Value {
 func getFieldByName(v reflect.StructValue, fieldname string) reflect.Value {
 	i := fieldIndex(v, fieldname);
 	if i < 0 {
-		panicln("field not found:", fieldname);
+		panicln(fmt.Sprintf("no field %s int %s", fieldname, v.Type().Name()));
 	}
 
 	return getField(v, i);
@@ -502,7 +565,7 @@ func typename(value reflect.Value) string {
 	case reflect.ArrayKind: name = "array";
 	case reflect.BoolKind: name = "bool";
 	case reflect.ChanKind: name = "chan";
-	case reflect.DotDotDotKind: name = "...";
+	case reflect.DotDotDotKind: name = "ellipsis";
 	case reflect.FloatKind: name = "float";
 	case reflect.Float32Kind: name = "float32";
 	case reflect.Float64Kind: name = "float64";
@@ -530,91 +593,177 @@ func typename(value reflect.Value) string {
 
 
 var defaults = map [int] expr {
-	reflect.ArrayKind: &field{"*", nil},
-	reflect.DotDotDotKind: &field{"*", nil},
-	reflect.InterfaceKind: &field{"*", nil},
-	reflect.MapKind: &field{"*", nil},
-	reflect.PtrKind: &field{"*", nil},
+	reflect.ArrayKind: &field{"*", ""},
+	reflect.DotDotDotKind: &field{"*", ""},
+	reflect.InterfaceKind: &field{"*", ""},
+	reflect.MapKind: &field{"*", ""},
+	reflect.PtrKind: &field{"*", ""},
+	reflect.StringKind: &literal{io.StringBytes("%s")},
 }
 
 var catchAll = &literal{io.StringBytes("%v")};
 
-func (f Format) getFormat(value reflect.Value) expr {
-	if fexpr, found := f[typename(value)]; found {
+func (f Format) getFormat(name string, value reflect.Value) expr {
+	/*
+	if name == "nil" {
+		fmt.Printf("value = %T %v, kind = %d\n", value, value, value.Kind());
+		panic();
+	}
+	*/
+	
+	if fexpr, found := f[name]; found {
 		return fexpr;
 	}
+	
+	if *debug {
+		fmt.Printf("no production for type: %s\n", name);
+	}
 
 	// no fexpr found - return kind-specific default value, if any
 	if fexpr, found := defaults[value.Kind()]; found {
 		return fexpr;
 	}
 
+	if *debug {
+		fmt.Printf("no default for type: %s\n", name);
+	}
+
 	return catchAll;
 }
 
 
 // Count the number of printf-style '%' formatters in s.
-// The result is 0, 1, or 2 (where 2 stands for 2 or more).
 //
 func percentCount(s []byte) int {
 	n := 0;
-	for i := 0; n < 2 && i < len(s); i++ {
-		// TODO should not count "%%"'s
+	for i := 0; i < len(s); i++ {
 		if s[i] == '%' {
-			n++;
+			i++;
+			if i >= len(s) || s[i] != '%' {  // don't count "%%"
+				n++;
+			}
 		}
 	}
 	return n;
 }
 
 
-func printf(w io.Write, format []byte, value reflect.Value) {
-	// TODO this seems a bit of a hack
-	if percentCount(format) == 1 {
-		// exactly one '%' format specifier - try to use it
-		fmt.Fprintf(w, string(format), value.Interface());
-	} else {
-		// 0 or more then 1 '%' format specifier - ignore them
-		w.Write(format);
+func rawPrintf(w io.Write, format []byte, value reflect.Value) {
+	// TODO find a better way to do this
+	x := value.Interface();
+	switch percentCount(format) {
+	case  0: w.Write(format);
+	case  1: fmt.Fprintf(w, string(format), x);
+	case  2: fmt.Fprintf(w, string(format), x, x);
+	case  3: fmt.Fprintf(w, string(format), x, x, x);
+	case  4: fmt.Fprintf(w, string(format), x, x, x, x);
+	default: panic("no support for more than 4 '%'-format chars yet");
 	}
 }
 
 
-// TODO once 6g bug found
-func print(s string, a ...) {
-	/*
-	f0 := reflect.NewValue(a).(reflect.StructValue).Field(0);
-	if t, is_iface := f0.(reflect.InterfaceValue); is_iface {
-		f0 = reflect.NewValue(t.Get());
+// TODO this should become a Go built-in
+func push(dst []int, x int) []int {
+	n := len(dst);
+	if n > cap(dst) {
+		panic("dst too small");
 	}
-	*/
-	fmt.Printf(s, a)
+	dst = dst[0 : n+1];
+	dst[n] = x;
+	return dst;
+}
+
+
+func append(dst, src []byte) []byte {
+	n, m := len(dst), len(src);
+	if n+m > cap(dst) {
+		panic("dst too small");
+	}
+	dst = dst[0 : n+m];
+	for i := 0; i < m; i++ {
+		dst[n+i] = src[i];
+	}
+	return dst;
+}
+
+
+type state struct {
+	f Format;
+	
+	// indentation
+	indent_text []byte;
+	indent_widths []int;
+}
+
+
+func (ps *state) init(f Format) {
+	ps.f = f;
+	ps.indent_text = make([]byte, 0, 1000);  // TODO don't use fixed cap
+	ps.indent_widths = make([]int, 0, 100);  // TODO don't use fixed cap
+}
+
+
+func (ps *state) indent(text []byte) {
+	ps.indent_widths = push(ps.indent_widths, len(ps.indent_text));
+	ps.indent_text = append(ps.indent_text, text);
+}
+
+
+func (ps *state) outdent() {
+	i := len(ps.indent_widths);
+	if i > 0 {
+		ps.indent_text = ps.indent_text[0 : ps.indent_widths[i-1]];
+		ps.indent_widths = ps.indent_widths[0 : i-1];
+	}
+}
+
+
+func (ps *state) printIndented(w io.Write, s []byte) {
+	// replace each '\n' with the indent + '\n'
+	i0 := 0;
+	for i := 0; i < len(s); i++ {
+		if s[i] == '\n' {
+			w.Write(s[i0 : i+1]);
+			w.Write(ps.indent_text);
+			i0 = i+1;
+		}
+	}
+	w.Write(s[i0 : len(s)]);
 }
 
 
-func (f Format) print(w io.Write, fexpr expr, value reflect.Value, index, level int) bool
+func (ps *state) printf(w io.Write, format []byte, value reflect.Value) {
+	if len(ps.indent_widths) == 0 {
+		// no indentation
+		rawPrintf(w, format, value);
+	} else {
+		// print into temporary buffer
+		var buf io.ByteBuffer;
+		rawPrintf(&buf, format, value);
+		ps.printIndented(w, buf.Data());
+	}
+}
+
+
+func (ps *state) print(w io.Write, fexpr expr, value reflect.Value, index, level int) bool
 
 // Returns true if a non-empty field value was found.
-func (f Format) print0(w io.Write, fexpr expr, value reflect.Value, index, level int) bool {
+func (ps *state) print0(w io.Write, fexpr expr, value reflect.Value, index, level int) bool {
 	if fexpr == nil {
 		return true;
 	}
 
-	if value == nil {
-		panic("should not be possible");
-	}
-
 	switch t := fexpr.(type) {
 	case *alternative:
 		// - print the contents of the first alternative with a non-empty field
 		// - result is true if there is at least one non-empty field
 		var buf io.ByteBuffer;
-		if f.print(&buf, t.x, value, index, level) {
+		if ps.print(&buf, t.x, value, 0, level) {
 			w.Write(buf.Data());
 			return true;
 		} else {
-			buf.Reset();
-			if f.print(&buf, t.y, value, 0, level) {
+			var buf io.ByteBuffer;
+			if ps.print(&buf, t.y, value, 0, level) {
 				w.Write(buf.Data());
 				return true;
 			}
@@ -625,27 +774,43 @@ func (f Format) print0(w io.Write, fexpr expr, value reflect.Value, index, level
 		// - print the contents of the sequence
 		// - result is true if there is no empty field
 		// TODO do we need to buffer here? why not?
-		b1 := f.print(w, t.x, value, index, level);
-		b2 := f.print(w, t.y, value, index, level);
+		b1 := ps.print(w, t.x, value, index, level);
+		b2 := ps.print(w, t.y, value, index, level);
 		return b1 && b2;
 
+	case *literal:
+		// - print the literal
+		// - result is always true (literal is never empty)
+		ps.printf(w, t.value, value);
+		return true;
+
+	case *indentation:
+		if t.iexpr != nil {
+			// indent
+			var buf io.ByteBuffer;
+			ps.print(&buf, t.iexpr, value, index, level);
+			ps.indent(buf.Data());
+
+		} else {
+			// outdent
+			ps.outdent();
+		}
+		return true;
+
 	case *field:
 		// - print the contents of the field
 		// - format is either the field format or the type-specific format
 		// - TODO look at field tag for default format
 		// - result is true if the field is not empty
-		switch t.name {
+		switch t.fname {
 		case "^":
 			// identity - value doesn't change
 
 		case "*":
 			// indirect
-			if value.Addr() == nil {  // TODO is this right?
-				return false;
-			}
 			switch v := value.(type) {
 			case reflect.ArrayValue:
-				if index < 0 || v.Len() <= index {
+				if v.Len() <= index {
 					return false;
 				}
 				value = v.Elem(index);
@@ -654,54 +819,54 @@ func (f Format) print0(w io.Write, fexpr expr, value reflect.Value, index, level
 				panic("reflection support for maps incomplete");
 
 			case reflect.PtrValue:
-				if v.Get() == nil {  // TODO is this right?
+				if v.Get() == nil {
 					return false;
 				}
 				value = v.Sub();
 
 			case reflect.InterfaceValue:
-				if v.Get() == nil {  // TODO is this right?
+				if v.Get() == nil {
 					return false;
 				}
 				value = v.Value();
 
 			default:
-				panic("not a ptr, array, map, or interface");  // TODO fix this
-			}
-
-			if value == nil {
-				fmt.Fprint(w, "NIL");  // TODO debugging
-				return false;
+				// TODO fix this
+				panic(fmt.Sprintf("error: * does not apply to `%s`\n", value.Type().Name()));
 			}
 
 		default:
 			// field
 			if s, is_struct := value.(reflect.StructValue); is_struct {
-				value = getFieldByName(s, t.name);
+				value = getFieldByName(s, t.fname);
 			} else {
-				panic ("not a struct");  // TODO fix this
+				// TODO fix this
+				panic(fmt.Sprintf("error: %s has no field `%s`\n", value.Type().Name(), t.fname));
 			}
 		}
 
 		// determine format
-		fexpr = t.fexpr;
-		if fexpr == nil {
-			// no field format - use type-specific format
-			fexpr = f.getFormat(value);
+		tname := t.tname;
+		if tname == "" {
+			tname = typename(value)
 		}
+		fexpr = ps.f.getFormat(tname, value);
 
-		return f.print(w, fexpr, value, index, level);
+		return ps.print(w, fexpr, value, index, level);
 
-	case *literal:
-		// - print the literal
-		// - result is always true (literal is never empty)
-		printf(w, t.value, value);
+	case *negation:
+		// TODO is this operation useful at all?
+		// print the contents of the option if is contains an empty field
+		var buf io.ByteBuffer;
+		if !ps.print(&buf, t.neg, value, 0, level) {
+			w.Write(buf.Data());
+		}
 		return true;
-
+		
 	case *option:
 		// print the contents of the option if it contains a non-empty field
 		var buf io.ByteBuffer;
-		if f.print(&buf, t.x, value, 0, level) {
+		if ps.print(&buf, t.opt, value, 0, level) {
 			w.Write(buf.Data());
 		}
 		return true;
@@ -709,14 +874,22 @@ func (f Format) print0(w io.Write, fexpr expr, value reflect.Value, index, level
 	case *repetition:
 		// print the contents of the repetition while there is a non-empty field
 		var buf io.ByteBuffer;
-		for i := 0; f.print(&buf, t.x, value, i, level); i++ {
+		for i := 0; ps.print(&buf, t.rep, value, i, level); i++ {
+			if i > 0 {
+				ps.print(w, t.div, value, i, level);
+			}
 			w.Write(buf.Data());
 			buf.Reset();
 		}
 		return true;
 		
 	case *custom:
-		return t.f(w, value.Interface(), t.name);
+		var buf io.ByteBuffer;
+		if t.form(&buf, value.Interface(), t.name) {
+			ps.printIndented(w, buf.Data());
+			return true;
+		}
+		return false;
 	}
 
 	panic("unreachable");
@@ -738,14 +911,14 @@ func printTrace(indent int, format string, a ...) {
 }
 
 
-func (f Format) print(w io.Write, fexpr expr, value reflect.Value, index, level int) bool {
-	if *debug {
+func (ps *state) print(w io.Write, fexpr expr, value reflect.Value, index, level int) bool {
+	if *trace {
 		printTrace(level, "%v, %d {\n", fexpr, /*value.Interface(), */index);
 	}
 
-	result := f.print0(w, fexpr, value, index, level+1);
+	result := ps.print0(w, fexpr, value, index, level+1);
 
-	if *debug {
+	if *trace {
 		printTrace(level, "} %v\n", result);
 	}
 	return result;
@@ -761,7 +934,9 @@ func (f Format) Fprint(w io.Write, args ...) {
 	value := reflect.NewValue(args).(reflect.StructValue);
 	for i := 0; i < value.Len(); i++ {
 		fld := getField(value, i);
-		f.print(w, f.getFormat(fld), fld, -1, 0);
+		var ps state;
+		ps.init(f);
+		ps.print(w, f.getFormat(typename(fld), fld), fld, 0, 0);
 	}
 }
 
@@ -770,7 +945,7 @@ func (f Format) Fprint(w io.Write, args ...) {
 // and writes to standard output.
 //
 func (f Format) Print(args ...) {
-	f.Print(os.Stdout, args);
+	f.Fprint(os.Stdout, args);
 }
 
 
diff --git a/usr/gri/pretty/format_test.go b/usr/gri/pretty/format_test.go
index e2948cc34..80401ba83 100644
--- a/usr/gri/pretty/format_test.go
+++ b/usr/gri/pretty/format_test.go
@@ -11,10 +11,10 @@ import (
 
 
 func check(t *testing.T, form, expected string, args ...) {
-	result := format.Parse(form).Sprint(args);
+	result := format.Parse(form, nil).Sprint(args);
 	if result != expected {
 		t.Errorf(
-			"format  : %s\nresult  : %s\nexpected: %s\n\n",
+			"format  : %s\nresult  : `%s`\nexpected: `%s`\n\n",
 			form, result, expected
 		)
 	}
@@ -22,13 +22,19 @@ func check(t *testing.T, form, expected string, args ...) {
 
 
 // ----------------------------------------------------------------------------
-// - formatting of basic type int
+// Syntax
 
-const F0 =
-	`int = "0x%x";`
+func TestA(t *testing.T) {
+	// TODO fill this in
+}
+
+
+// ----------------------------------------------------------------------------
+// - formatting of basic types
 
 func Test0(t *testing.T) {
-	check(t, F0, "0x2a", 42);
+	check(t, `bool = "%v"`, "false", false);
+	check(t, `int = "%b %d %o 0x%x"`, "101010 42 52 0x2a", 42);
 }
 
 
@@ -60,7 +66,7 @@ type T2 struct {
 const F2a =
 	F1 +
 	`pointer = *;`
-	`format.T2 = s ["-" p "-"];`;
+	`format.T2 = s ["-" p "-"];`
 	
 const F2b =
 	F1 +
@@ -82,14 +88,43 @@ type T3 struct {
 }
 
 const F3a =
-	`format.T3 = s  { " " a a "," };`;
+	`format.T3 = s  {" " a a / ","};`
 
 const F3b =
-	`format.T3 = [a:""] s | "nothing";`;  // use 'a' to select alternative w/o printing a
+	`nil = ;`
+	`empty = *:nil;`
+	`format.T3 = s [a:empty ": " {a / "-"}]`
 
 func Test3(t *testing.T) {
 	check(t, F3a, "foo", T3{"foo", nil});
-	check(t, F3a, "foo 00, 11, 22,", T3{"foo", []int{0, 1, 2}});
-	//check(t, F3b, "nothing", T3{"bar", nil});  // TODO fix this
-	check(t, F3b, "bar", T3{"bar", []int{0}});
+	check(t, F3a, "foo 00, 11, 22", T3{"foo", []int{0, 1, 2}});
+	check(t, F3b, "bar", T3{"bar", nil});
+	check(t, F3b, "bal: 2-3-5", T3{"bal", []int{2, 3, 5}});
+}
+
+
+// ----------------------------------------------------------------------------
+// - formatting of a struct with alternative field
+
+type T4 struct {
+	x *int;
+	a []int;
+}
+
+const F4a =
+	`nil = ;`
+	`empty = *:nil;`
+	`format.T4 = "<" (x:empty x | "-") ">" `
+
+const F4b =
+	`nil = ;`
+	`empty = *:nil;`
+	`format.T4 = "<" (a:empty {a / ", "} | "-") ">" `
+
+func Test4(t *testing.T) {
+	x := 7;
+	check(t, F4a, "<->", T4{nil, nil});
+	check(t, F4a, "<7>", T4{&x, nil});
+	check(t, F4b, "<->", T4{nil, nil});
+	check(t, F4b, "<2, 3, 7>", T4{nil, []int{2, 3, 7}});
 }
diff --git a/usr/gri/pretty/pretty.go b/usr/gri/pretty/pretty.go
index 81bb4d45e..0f4bafa25 100644
--- a/usr/gri/pretty/pretty.go
+++ b/usr/gri/pretty/pretty.go
@@ -66,7 +66,7 @@ func makeTabwriter(writer io.Write) *tabwriter.Writer {
 	if *usetabs {
 		padchar = '\t';
 	}
-	return tabwriter.NewWriter(writer, *tabwidth, 1, padchar, tabwriter.FilterHTML);
+	return tabwriter.NewWriter(writer, *tabwidth, 1, padchar, 0);
 }
 
 
@@ -114,7 +114,7 @@ func main() {
 		fmt.Fprintf(os.Stderr, "%s: %v\n", ast_txt, err);
 		sys.Exit(1);
 	}
-	ast_format := format.Parse(src);
+	ast_format := format.Parse(src, nil);
 	if ast_format == nil {
 		fmt.Fprintf(os.Stderr, "%s: format errors\n", ast_txt);
 		sys.Exit(1);