added documentation and did some slight restructuring. it's party time.

11 files changed, 284 insertions, 304 deletions

diff --git a/nexgb/xgbgen/context.go b/nexgb/xgbgen/context.go
index 3e484f3..d433531 100644
--- a/nexgb/xgbgen/context.go
+++ b/nexgb/xgbgen/context.go
@@ -8,6 +8,8 @@ import (
 	"time"
 )
 
+// Context represents the protocol we're converting to Go, and a writer
+// buffer to write the Go source to.
 type Context struct {
 	protocol *Protocol
 	out      *bytes.Buffer
diff --git a/nexgb/xgbgen/doc.go b/nexgb/xgbgen/doc.go
new file mode 100644
index 0000000..4ba6145
--- /dev/null
+++ b/nexgb/xgbgen/doc.go
@@ -0,0 +1,74 @@
+/*
+xgbgen constructs Go source files from xproto XML description files. xgbgen
+accomplishes the same task as the Python code generator for XCB and xpyb.
+
+Usage:
+	xgbgen [flags] some-protocol.xml
+
+The flags are:
+	--proto-path path
+		The path to a directory containing xproto XML description files.
+		This is only necessary when 'some-protocol.xml' imports other
+		protocol files.
+	--gofmt=true
+		When false, the outputted Go code will not be gofmt'd. And it won't
+		be very pretty at all. This is typically useful if there are syntax
+		errors that need to be debugged in code generation. gofmt will hiccup;
+		this will allow you to see the raw code.
+
+How it works
+
+xgbgen works by parsing the input XML file using Go's encoding/xml package.
+The majority of this work is done in xml.go and xml_fields.go, where the
+appropriate types are declared.
+
+Due to the nature of the XML in the protocol description files, the types
+required to parse the XML are not well suited to reasoning about code
+generation. Because of this, all data parsed in the XML types is translated
+into more reasonable types. This translation is done in translation.go,
+and is mainly grunt work. (The only interesting tidbits are the translation
+of XML names to Go source names, and connecting fields with their
+appropriate types.)
+
+The organization of these types is greatly
+inspired by the description of the XML found here:
+http://cgit.freedesktop.org/xcb/proto/tree/doc/xml-xcb.txt
+
+These types come with a lot of supporting methods to make their use in
+code generation easier. They can be found in expression.go, field.go,
+protocol.go, request_reply.go and type.go. Of particular interest are
+expression evaluation and size calculation (in bytes).
+
+These types also come with supporting methods that convert their
+representation into Go source code. I've quartered such methods in
+go.go, go_error.go, go_event.go, go_list.go, go_request_reply.go,
+go_single_field.go, go_struct.go and go_union.go. The idea is to keep
+as much of the Go specific code generation in one area as possible. Namely,
+while not *all* Go related code is found in the 'go*.go' files, *most*
+of it is. (If there's any interest in using xgbgen for other languages,
+I'd be happy to try and make xgbgen a little more friendly in this regard.
+I did, however, design xgbgen with this in mind, so it shouldn't involve
+anything as serious as a re-design.)
+
+Why
+
+I wrote xgbgen because I found the existing code generator that was written in
+Python to be unwieldy. In particular, static and strong typing greatly helped
+me reason better about the code generation task.
+
+What does not work
+
+The core X protocol should be completely working. As far as I know, most
+extensions should work too, although I've only tested (and not much) the
+Xinerama and RandR extensions.
+
+XKB does not work. I don't have any real plans of working on this unless there
+is demand and I have some test cases to work with. (i.e., even if I could get
+something generated for XKB, I don't have the inclination to understand it
+enough to verify that it works.) XKB poses several extremely difficult
+problems that XCB also has trouble with. More info on that can be found at
+http://cgit.freedesktop.org/xcb/libxcb/tree/doc/xkb_issues and
+http://cgit.freedesktop.org/xcb/libxcb/tree/doc/xkb_internals.
+
+*/
+package main
diff --git a/nexgb/xgbgen/expression.go b/nexgb/xgbgen/expression.go
index 2350979..721ebfd 100644
--- a/nexgb/xgbgen/expression.go
+++ b/nexgb/xgbgen/expression.go
@@ -5,11 +5,32 @@ import (
 	"log"
 )
 
+// Expression represents all the different forms of expressions possible in
+// side an XML protocol description file. It's also received a few custom
+// addendums to make applying special functions (like padding) easier.
 type Expression interface {
+	// Concrete determines whether this particular expression can be computed
+	// to some constant value inside xgbgen. (The alternative is that the
+	// expression can only be computed with values at run time of the
+	// generated code.)
 	Concrete() bool
+
+	// Eval evaluates a concrete expression. It is an error to call Eval
+	// on any expression that is not concrete (or contains any sub-expression
+	// that is not concrete).
 	Eval() uint
+
+	// Reduce attempts to evaluate any concrete sub-expressions.
+	// i.e., (1 + 2 * (5 + 1 + someSizeOfStruct) reduces to
+	// (3 * (6 + someSizeOfStruct)).
+	// 'prefix' is used preprended to any field reference name.
 	Reduce(prefix string) string
+
+	// String is an alias for Reduce("")
 	String() string
+
+	// Initialize makes sure all names in this expression and any subexpressions
+	// have been translated to Go source names.
 	Initialize(p *Protocol)
 }
 
@@ -41,12 +62,17 @@ func (e *Function) Initialize(p *Protocol) {
 	e.Expr.Initialize(p)
 }
 
+// BinaryOp is an expression that performs some operation (defined in the XML
+// file) with Expr1 and Expr2 as operands.
 type BinaryOp struct {
 	Op    string
 	Expr1 Expression
 	Expr2 Expression
 }
 
+// newBinaryOp constructs a new binary expression when both expr1 and expr2
+// are not nil. If one or both are nil, then the non-nil expression is
+// returned unchanged or nil is returned.
 func newBinaryOp(op string, expr1, expr2 Expression) Expression {
 	switch {
 	case expr1 != nil && expr2 != nil:
@@ -124,6 +150,8 @@ func (e *BinaryOp) Initialize(p *Protocol) {
 	e.Expr2.Initialize(p)
 }
 
+// UnaryOp is the same as BinaryOp, except it's a unary operator with only
+// one sub-expression.
 type UnaryOp struct {
 	Op   string
 	Expr Expression
@@ -158,6 +186,8 @@ func (e *UnaryOp) Initialize(p *Protocol) {
 	e.Expr.Initialize(p)
 }
 
+// Padding represents the application of the 'pad' function to some
+// sub-expression.
 type Padding struct {
 	Expr Expression
 }
@@ -185,6 +215,8 @@ func (e *Padding) Initialize(p *Protocol) {
 	e.Expr.Initialize(p)
 }
 
+// PopCount represents the application of the 'PopCount' function to
+// some sub-expression.
 type PopCount struct {
 	Expr Expression
 }
@@ -212,6 +244,7 @@ func (e *PopCount) Initialize(p *Protocol) {
 	e.Expr.Initialize(p)
 }
 
+// Value represents some constant integer.
 type Value struct {
 	v uint
 }
@@ -234,6 +267,7 @@ func (e *Value) String() string {
 
 func (e *Value) Initialize(p *Protocol) {}
 
+// Bit represents some bit whose value is computed by '1 << bit'.
 type Bit struct {
 	b uint
 }
@@ -256,6 +290,8 @@ func (e *Bit) String() string {
 
 func (e *Bit) Initialize(p *Protocol) {}
 
+// FieldRef represents a reference to some variable in the generated code
+// with name Name.
 type FieldRef struct {
 	Name string
 }
@@ -285,6 +321,9 @@ func (e *FieldRef) Initialize(p *Protocol) {
 	e.Name = SrcName(p, e.Name)
 }
 
+// EnumRef represents a reference to some enumeration field.
+// EnumKind is the "group" an EnumItem is the name of the specific enumeration 
+// value inside that group.
 type EnumRef struct {
 	EnumKind Type
 	EnumItem string
@@ -312,6 +351,8 @@ func (e *EnumRef) Initialize(p *Protocol) {
 	e.EnumItem = SrcName(p, e.EnumItem)
 }
 
+// SumOf represents a summation of the variable in the generated code named by
+// Name. It is not currently used. (It's XKB voodoo.)
 type SumOf struct {
 	Name string
 }
diff --git a/nexgb/xgbgen/field.go b/nexgb/xgbgen/field.go
index 5041f77..725f3de 100644
--- a/nexgb/xgbgen/field.go
+++ b/nexgb/xgbgen/field.go
@@ -6,20 +6,48 @@ import (
 	"strings"
 )
 
+// Field corresponds to any field described in an XML protocol description
+// file. This includes struct fields, union fields, request fields,
+// reply fields and so on.
+// To make code generation easier, fields that have types are also stored.
+// Note that not all fields support all methods defined in this interface.
+// For instance, a padding field does not have a source name.
 type Field interface {
+	// Initialize sets up the source name of this field.
 	Initialize(p *Protocol)
+
+	// SrcName is the Go source name of this field.
 	SrcName() string
+
+	// XmlName is the name of this field from the XML file.
 	XmlName() string
+
+	// SrcType is the Go source type name of this field.
 	SrcType() string
+
+	// Size returns an expression that computes the size (in bytes)
+	// of this field.
 	Size() Size
 
+	// Define writes the Go code to declare this field (in a struct definition).
 	Define(c *Context)
+
+	// Read writes the Go code to convert a byte slice to a Go value
+	// of this field.
+	// 'prefix' is the prefix of the name of the Go value.
 	Read(c *Context, prefix string)
+
+	// Write writes the Go code to convert a Go value to a byte slice of
+	// this field.
+	// 'prefix' is the prefix of the name of the Go value.
 	Write(c *Context, prefix string)
 }
 
 func (pad *PadField) Initialize(p *Protocol) {}
 
+// PadField represents any type of padding. It is omitted from
+// definitions, but is used in Read/Write to increment the buffer index.
+// It is also used in size calculation.
 type PadField struct {
 	Bytes uint
 }
@@ -40,6 +68,8 @@ func (p *PadField) Size() Size {
 	return newFixedSize(p.Bytes)
 }
 
+// SingleField represents most of the fields in an XML protocol description.
+// It corresponds to any single value.
 type SingleField struct {
 	srcName string
 	xmlName string
@@ -67,6 +97,7 @@ func (f *SingleField) Size() Size {
 	return f.Type.Size()
 }
 
+// ListField represents a list of values.
 type ListField struct {
 	srcName    string
 	xmlName    string
@@ -89,6 +120,9 @@ func (f *ListField) SrcType() string {
 	return fmt.Sprintf("[]%s", f.Type.SrcName())
 }
 
+// Length computes the *number* of values in a list.
+// If this ListField does not have any length expression, we throw our hands
+// up and simply compute the 'len' of the field name of this list.
 func (f *ListField) Length() Size {
 	if f.LengthExpr == nil {
 		return newExpressionSize(&Function{
@@ -101,6 +135,12 @@ func (f *ListField) Length() Size {
 	return newExpressionSize(f.LengthExpr)
 }
 
+// Size computes the *size* of a list (in bytes).
+// It it typically a simple matter of multiplying the length of the list by
+// the size of the type of the list.
+// But if it's a list of struct where the struct has a list field, we use a 
+// special function written in go_struct.go to compute the size (since the
+// size in this case can only be computed recursively).
 func (f *ListField) Size() Size {
 	simpleLen := &Function{
 		Name: "pad",
@@ -120,11 +160,6 @@ func (f *ListField) Size() Size {
 		}
 	case *Union:
 		return newExpressionSize(simpleLen)
-		// sizeFun := &Function{ 
-			// Name: fmt.Sprintf("%sListSize", f.Type.SrcName()), 
-			// Expr: &FieldRef{Name: f.SrcName()}, 
-		// } 
-		// return newExpressionSize(sizeFun) 
 	case *Base:
 		return newExpressionSize(simpleLen)
 	case *Resource:
@@ -145,10 +180,14 @@ func (f *ListField) Initialize(p *Protocol) {
 	}
 }
 
+// LocalField is exactly the same as a regular SingleField, except it isn't
+// sent over the wire. (i.e., it's probably used to compute an ExprField).
 type LocalField struct {
 	*SingleField
 }
 
+// ExprField is a field that is not parameterized, but is computed from values
+// of other fields.
 type ExprField struct {
 	srcName string
 	xmlName string
@@ -178,6 +217,9 @@ func (f *ExprField) Initialize(p *Protocol) {
 	f.Expr.Initialize(p)
 }
 
+// ValueField represents two fields in one: a mask and a list of 4-byte
+// integers. The mask specifies which kinds of values are in the list.
+// (i.e., See ConfigureWindow, CreateWindow, ChangeWindowAttributes, etc.)
 type ValueField struct {
 	Parent interface{}
 	MaskType Type
@@ -197,6 +239,10 @@ func (f *ValueField) SrcType() string {
 	return f.MaskType.SrcName()
 }
 
+// Size computes the size in bytes of the combination of the mask and list
+// in this value field.
+// The expression to compute this looks complicated, but it's really just
+// the number of bits set in the mask multiplied 4 (and padded of course).
 func (f *ValueField) Size() Size {
 	maskSize := f.MaskType.Size()
 	listSize := newExpressionSize(&Function{
@@ -234,6 +280,8 @@ func (f *ValueField) Initialize(p *Protocol) {
 	f.ListName = SrcName(p, f.ListName)
 }
 
+// SwitchField represents a 'switch' element in the XML protocol description
+// file. It is not currently used. (i.e., it is XKB voodoo.)
 type SwitchField struct {
 	Name     string
 	Expr     Expression
@@ -270,6 +318,8 @@ func (f *SwitchField) Initialize(p *Protocol) {
 	}
 }
 
+// Bitcase represents a single bitcase inside a switch expression.
+// It is not currently used. (i.e., it's XKB voodoo.)
 type Bitcase struct {
 	Fields []Field
 	Expr   Expression
diff --git a/nexgb/xgbgen/misc.go b/nexgb/xgbgen/misc.go
index 13c4cc2..85d788f 100644
--- a/nexgb/xgbgen/misc.go
+++ b/nexgb/xgbgen/misc.go
@@ -7,7 +7,7 @@ import (
 
 // AllCaps is a regex to test if a string identifier is made of
 // all upper case letters.
-var AllCaps = regexp.MustCompile("^[A-Z0-9]+$")
+var allCaps = regexp.MustCompile("^[A-Z0-9]+$")
 
 // popCount counts number of bits 'set' in mask.
 func popCount(mask uint) uint {
@@ -30,7 +30,7 @@ func pad(n int) int {
 // first letter of each chunk, and smushes'em back together.
 func splitAndTitle(s string) string {
 	// If the string is all caps, lower it and capitalize first letter.
-	if AllCaps.MatchString(s) {
+	if allCaps.MatchString(s) {
 		return strings.Title(strings.ToLower(s))
 	}
 
diff --git a/nexgb/xgbgen/protocol.go b/nexgb/xgbgen/protocol.go
new file mode 100644
index 0000000..505b400
--- /dev/null
+++ b/nexgb/xgbgen/protocol.go
@@ -0,0 +1,41 @@
+package main
+
+import (
+	"strings"
+)
+
+// Protocol is a type that encapsulates all information about one
+// particular XML file. It also contains links to other protocol types
+// if this protocol imports other other extensions. The import relationship
+// is recursive.
+type Protocol struct {
+	Name         string
+	ExtXName     string
+	ExtName      string
+	MajorVersion string
+	MinorVersion string
+
+	Imports  []*Protocol
+	Types    []Type
+	Requests []*Request
+}
+
+// Initialize traverses all structures, looks for 'Translation' type,
+// and looks up the real type in the namespace. It also sets the source
+// name for all relevant fields/structures.
+// This is necessary because we don't traverse the XML in order initially.
+func (p *Protocol) Initialize() {
+	for _, typ := range p.Types {
+		typ.Initialize(p)
+	}
+	for _, req := range p.Requests {
+		req.Initialize(p)
+	}
+}
+
+// isExt returns true if this protocol is an extension.
+// i.e., it's name isn't "xproto".
+func (p *Protocol) isExt() bool {
+	return strings.ToLower(p.Name) == "xproto"
+}
+
diff --git a/nexgb/xgbgen/representation.go b/nexgb/xgbgen/request_reply.go
index 62a3eb2..7cd2859 100644
--- a/nexgb/xgbgen/representation.go
+++ b/nexgb/xgbgen/request_reply.go
@@ -7,40 +7,19 @@ import (
 	"unicode"
 )
 
-type Protocol struct {
-	Name         string
-	ExtXName     string
-	ExtName      string
-	MajorVersion string
-	MinorVersion string
-
-	Imports  []*Protocol
-	Types    []Type
-	Requests []*Request
-}
-
-// Initialize traverses all structures, looks for 'Translation' type,
-// and looks up the real type in the namespace. It also sets the source
-// name for all relevant fields/structures.
-// This is necessary because we don't traverse the XML in order initially.
-func (p *Protocol) Initialize() {
-	for _, typ := range p.Types {
-		typ.Initialize(p)
-	}
-	for _, req := range p.Requests {
-		req.Initialize(p)
-	}
-}
-
+// Request represents all XML 'request' nodes.
+// If the request doesn't have a reply, Reply is nil.
 type Request struct {
-	srcName string
-	xmlName string
+	srcName string // The Go name of this request.
+	xmlName string // The XML name of this request.
 	Opcode  int
-	Combine bool
-	Fields  []Field
-	Reply   *Reply
+	Combine bool // Not currently used.
+	Fields  []Field // All fields in the request.
+	Reply   *Reply // A reply, if one exists for this request.
 }
 
+// Initialize creates the proper Go source name for this request.
+// It also initializes the reply if one exists, and all fields in this request.
 func (r *Request) Initialize(p *Protocol) {
 	r.srcName = SrcName(p, r.xmlName)
 	if p.Name != "xproto" {
@@ -63,6 +42,9 @@ func (r *Request) XmlName() string {
 	return r.xmlName
 }
 
+// ReplyName gets the Go source name of the function that generates a
+// reply type from a slice of bytes.
+// The generated function is not currently exported.
 func (r *Request) ReplyName() string {
 	if r.Reply == nil {
 		log.Panicf("Cannot call 'ReplyName' on request %s, which has no reply.",
@@ -73,6 +55,8 @@ func (r *Request) ReplyName() string {
 	return fmt.Sprintf("%sReply", lower)
 }
 
+// ReplyTypeName gets the Go source name of the type holding all reply data
+// for this request.
 func (r *Request) ReplyTypeName() string {
 	if r.Reply == nil {
 		log.Panicf("Cannot call 'ReplyName' on request %s, which has no reply.",
@@ -81,12 +65,17 @@ func (r *Request) ReplyTypeName() string {
 	return fmt.Sprintf("%sReply", r.SrcName())
 }
 
+// ReqName gets the Go source name of the function that generates a byte
+// slice from a list of parameters.
+// The generated function is not currently exported.
 func (r *Request) ReqName() string {
 	name := r.SrcName()
 	lower := string(unicode.ToLower(rune(name[0]))) + name[1:]
 	return fmt.Sprintf("%sRequest", lower)
 }
 
+// CookieName gets the Go source name of the type that holds cookies for
+// this request.
 func (r *Request) CookieName() string {
 	return fmt.Sprintf("%sCookie", r.SrcName())
 }
@@ -99,6 +88,11 @@ func (r *Request) CookieName() string {
 func (r *Request) Size(c *Context) Size {
 	size := newFixedSize(0)
 
+	// If this is a core protocol request, we squeeze in an extra byte of
+	// data (from the fields below) between the opcode and the size of the 
+	// request. In an extension request, this byte is always occupied
+	// by the opcode of the request (while the first byte is always occupied
+	// by the opcode of the extension).
 	if c.protocol.Name == "xproto" {
 		size = size.Add(newFixedSize(3))
 	} else {
@@ -107,7 +101,7 @@ func (r *Request) Size(c *Context) Size {
 
 	for _, field := range r.Fields {
 		switch field.(type) {
-		case *LocalField:
+		case *LocalField: // local fields don't go over the wire
 			continue
 		case *SingleField:
 			// mofos!!!
@@ -126,10 +120,16 @@ func (r *Request) Size(c *Context) Size {
 	})
 }
 
+// Reply encapsulates the fields associated with a 'reply' element.
 type Reply struct {
 	Fields []Field
 }
 
+// Size gets the number of bytes in this request's reply.
+// A reply always has at least 7 bytes:
+// 1 byte: A reply discriminant (first byte set to 1)
+// 2 bytes: A sequence number
+// 4 bytes: Number of additional bytes in 4-byte units past initial 32 bytes.
 func (r *Reply) Size() Size {
 	size := newFixedSize(0)
 
diff --git a/nexgb/xgbgen/size.go b/nexgb/xgbgen/size.go
index 70edb8f..d8d3ac3 100644
--- a/nexgb/xgbgen/size.go
+++ b/nexgb/xgbgen/size.go
@@ -1,21 +1,30 @@
 package main
 
+// Size corresponds to an expression that represents the number of bytes
+// in some *thing*. Generally, sizes are used to allocate buffers and to
+// inform X how big requests are.
+// Size is basically a thin layer over an Expression that yields easy methods
+// for adding and multiplying sizes.
 type Size struct {
 	Expression
 }
 
+// newFixedSize creates a new Size with some fixed and known value.
 func newFixedSize(fixed uint) Size {
 	return Size{&Value{v: fixed}}
 }
 
+// newExpressionSize creates a new Size with some expression.
 func newExpressionSize(variable Expression) Size {
 	return Size{variable}
 }
 
+// Add adds s1 and s2 and returns a new Size.
 func (s1 Size) Add(s2 Size) Size {
 	return Size{newBinaryOp("+", s1, s2)}
 }
 
+// Multiply mupltiplies s1 and s2 and returns a new Size.
 func (s1 Size) Multiply(s2 Size) Size {
 	return Size{newBinaryOp("*", s1, s2)}
 }
diff --git a/nexgb/xgbgen/xml.go b/nexgb/xgbgen/xml.go
index 1b2f89a..df21433 100644
--- a/nexgb/xgbgen/xml.go
+++ b/nexgb/xgbgen/xml.go
@@ -18,19 +18,19 @@ type XML struct {
 	// Types for all top-level elements.
 	// First are the simple ones.
 	Imports     XMLImports     `xml:"import"`
-	Enums       XMLEnums       `xml:"enum"`
-	Xids        XMLXids        `xml:"xidtype"`
-	XidUnions   XMLXids        `xml:"xidunion"`
-	TypeDefs    XMLTypeDefs    `xml:"typedef"`
-	EventCopies XMLEventCopies `xml:"eventcopy"`
-	ErrorCopies XMLErrorCopies `xml:"errorcopy"`
+	Enums       []*XMLEnum       `xml:"enum"`
+	Xids        []*XMLXid        `xml:"xidtype"`
+	XidUnions   []*XMLXid        `xml:"xidunion"`
+	TypeDefs    []*XMLTypeDef    `xml:"typedef"`
+	EventCopies []*XMLEventCopy `xml:"eventcopy"`
+	ErrorCopies []*XMLErrorCopy `xml:"errorcopy"`
 
 	// Here are the complex ones, i.e., anything with "structure contents"
-	Structs  XMLStructs  `xml:"struct"`
-	Unions   XMLUnions   `xml:"union"`
-	Requests XMLRequests `xml:"request"`
-	Events   XMLEvents   `xml:"event"`
-	Errors   XMLErrors   `xml:"error"`
+	Structs  []*XMLStruct  `xml:"struct"`
+	Unions   []*XMLUnion   `xml:"union"`
+	Requests []*XMLRequest `xml:"request"`
+	Events   []*XMLEvent   `xml:"event"`
+	Errors   []*XMLError   `xml:"error"`
 }
 
 type XMLImports []*XMLImport
@@ -60,8 +60,6 @@ type XMLImport struct {
 	xml  *XML   `xml:"-"`
 }
 
-type XMLEnums []XMLEnum
-
 type XMLEnum struct {
 	Name  string         `xml:"name,attr"`
 	Items []*XMLEnumItem `xml:"item"`
@@ -72,77 +70,69 @@ type XMLEnumItem struct {
 	Expr *XMLExpression `xml:",any"`
 }
 
-type XMLXids []*XMLXid
-
 type XMLXid struct {
 	XMLName xml.Name
 	Name    string `xml:"name,attr"`
 }
 
-type XMLTypeDefs []*XMLTypeDef
-
 type XMLTypeDef struct {
 	Old string `xml:"oldname,attr"`
 	New string `xml:"newname,attr"`
 }
 
-type XMLEventCopies []*XMLEventCopy
-
 type XMLEventCopy struct {
 	Name   string `xml:"name,attr"`
 	Number int    `xml:"number,attr"`
 	Ref    string `xml:"ref,attr"`
 }
 
-type XMLErrorCopies []*XMLErrorCopy
-
 type XMLErrorCopy struct {
 	Name   string `xml:"name,attr"`
 	Number int    `xml:"number,attr"`
 	Ref    string `xml:"ref,attr"`
 }
 
-type XMLStructs []*XMLStruct
-
 type XMLStruct struct {
 	Name   string    `xml:"name,attr"`
-	Fields XMLFields `xml:",any"`
+	Fields []*XMLField `xml:",any"`
 }
 
-type XMLUnions []*XMLUnion
-
 type XMLUnion struct {
 	Name   string    `xml:"name,attr"`
-	Fields XMLFields `xml:",any"`
+	Fields []*XMLField `xml:",any"`
 }
 
-type XMLRequests []*XMLRequest
-
 type XMLRequest struct {
 	Name    string    `xml:"name,attr"`
 	Opcode  int       `xml:"opcode,attr"`
 	Combine bool      `xml:"combine-adjacent,attr"`
-	Fields  XMLFields `xml:",any"`
+	Fields  []*XMLField `xml:",any"`
 	Reply   *XMLReply `xml:"reply"`
 }
 
 type XMLReply struct {
-	Fields XMLFields `xml:",any"`
+	Fields []*XMLField `xml:",any"`
 }
 
-type XMLEvents []*XMLEvent
-
 type XMLEvent struct {
 	Name       string    `xml:"name,attr"`
 	Number     int       `xml:"number,attr"`
 	NoSequence bool      `xml:"no-sequence-number,attr"`
-	Fields     XMLFields `xml:",any"`
+	Fields     []*XMLField `xml:",any"`
 }
 
-type XMLErrors []*XMLError
-
 type XMLError struct {
 	Name   string    `xml:"name,attr"`
 	Number int       `xml:"number,attr"`
-	Fields XMLFields `xml:",any"`
+	Fields []*XMLField `xml:",any"`
+}
+
+type XMLExpression struct {
+	XMLName xml.Name
+
+	Exprs []*XMLExpression `xml:",any"`
+
+	Data string `xml:",chardata"`
+	Op   string `xml:"op,attr"`
+	Ref  string `xml:"ref,attr"`
 }
diff --git a/nexgb/xgbgen/xml_expression.go b/nexgb/xgbgen/xml_expression.go
deleted file mode 100644
index 2989668..0000000
--- a/nexgb/xgbgen/xml_expression.go
+++ /dev/null
@@ -1,160 +0,0 @@
-package main
-
-import (
-	"encoding/xml"
-	"fmt"
-	"log"
-	"strconv"
-)
-
-type XMLExpression struct {
-	XMLName xml.Name
-
-	Exprs []*XMLExpression `xml:",any"`
-
-	Data string `xml:",chardata"`
-	Op   string `xml:"op,attr"`
-	Ref  string `xml:"ref,attr"`
-}
-
-func newValueExpression(v uint) *XMLExpression {
-	return &XMLExpression{
-		XMLName: xml.Name{Local: "value"},
-		Data:    fmt.Sprintf("%d", v),
-	}
-}
-
-// String is for debugging. For actual use, please use 'Morph'.
-func (e *XMLExpression) String() string {
-	switch e.XMLName.Local {
-	case "op":
-		return fmt.Sprintf("(%s %s %s)", e.Exprs[0], e.Op, e.Exprs[1])
-	case "unop":
-		return fmt.Sprintf("(%s (%s))", e.Op, e.Exprs[0])
-	case "popcount":
-		return fmt.Sprintf("popcount(%s)", e.Exprs[0])
-	case "fieldref":
-		fallthrough
-	case "value":
-		return fmt.Sprintf("%s", e.Data)
-	case "bit":
-		return fmt.Sprintf("(1 << %s)", e.Data)
-	case "enumref":
-		return fmt.Sprintf("%s%s", e.Ref, e.Data)
-	case "sumof":
-		return fmt.Sprintf("sum(%s)", e.Ref)
-	default:
-		log.Panicf("Unrecognized expression element: %s", e.XMLName.Local)
-	}
-
-	panic("unreachable")
-}
-
-// Eval is used to *attempt* to compute a concrete value for a particular
-// expression. This is used in the initial setup to instantiate values for
-// empty items in enums.
-// We can't compute a concrete value for expressions that rely on a context,
-// i.e., some field value.
-func (e *XMLExpression) Eval() uint {
-	switch e.XMLName.Local {
-	case "op":
-		if len(e.Exprs) != 2 {
-			log.Panicf("'op' found %d expressions; expected 2.", len(e.Exprs))
-		}
-		return e.BinaryOp(e.Exprs[0], e.Exprs[1]).Eval()
-	case "unop":
-		if len(e.Exprs) != 1 {
-			log.Panicf("'unop' found %d expressions; expected 1.", len(e.Exprs))
-		}
-		return e.UnaryOp(e.Exprs[0]).Eval()
-	case "popcount":
-		if len(e.Exprs) != 1 {
-			log.Panicf("'popcount' found %d expressions; expected 1.",
-				len(e.Exprs))
-		}
-		return popCount(e.Exprs[0].Eval())
-	case "value":
-		val, err := strconv.Atoi(e.Data)
-		if err != nil {
-			log.Panicf("Could not convert '%s' in 'value' expression to int.",
-				e.Data)
-		}
-		return uint(val)
-	case "bit":
-		bit, err := strconv.Atoi(e.Data)
-		if err != nil {
-			log.Panicf("Could not convert '%s' in 'bit' expression to int.",
-				e.Data)
-		}
-		if bit < 0 || bit > 31 {
-			log.Panicf("A 'bit' literal must be in the range [0, 31], but "+
-				" is %d", bit)
-		}
-		return 1 << uint(bit)
-	case "fieldref":
-		log.Panicf("Cannot compute concrete value of 'fieldref' in "+
-			"expression '%s'.", e)
-	case "enumref":
-		log.Panicf("Cannot compute concrete value of 'enumref' in "+
-			"expression '%s'.", e)
-	case "sumof":
-		log.Panicf("Cannot compute concrete value of 'sumof' in "+
-			"expression '%s'.", e)
-	}
-
-	log.Panicf("Unrecognized tag '%s' in expression context. Expected one of "+
-		"op, fieldref, value, bit, enumref, unop, sumof or popcount.",
-		e.XMLName.Local)
-	panic("unreachable")
-}
-
-func (e *XMLExpression) BinaryOp(oprnd1, oprnd2 *XMLExpression) *XMLExpression {
-	if e.XMLName.Local != "op" {
-		log.Panicf("Cannot perform binary operation on non-op expression: %s",
-			e.XMLName.Local)
-	}
-	if len(e.Op) == 0 {
-		log.Panicf("Cannot perform binary operation without operator for: %s",
-			e.XMLName.Local)
-	}
-
-	wrap := newValueExpression
-	switch e.Op {
-	case "+":
-		return wrap(oprnd1.Eval() + oprnd2.Eval())
-	case "-":
-		return wrap(oprnd1.Eval() + oprnd2.Eval())
-	case "*":
-		return wrap(oprnd1.Eval() * oprnd2.Eval())
-	case "/":
-		return wrap(oprnd1.Eval() / oprnd2.Eval())
-	case "&amp;":
-		return wrap(oprnd1.Eval() & oprnd2.Eval())
-	case "&lt;&lt;":
-		return wrap(oprnd1.Eval() << oprnd2.Eval())
-	}
-
-	log.Panicf("Invalid binary operator '%s' for '%s' expression.",
-		e.Op, e.XMLName.Local)
-	panic("unreachable")
-}
-
-func (e *XMLExpression) UnaryOp(oprnd *XMLExpression) *XMLExpression {
-	if e.XMLName.Local != "unop" {
-		log.Panicf("Cannot perform unary operation on non-unop expression: %s",
-			e.XMLName.Local)
-	}
-	if len(e.Op) == 0 {
-		log.Panicf("Cannot perform unary operation without operator for: %s",
-			e.XMLName.Local)
-	}
-
-	switch e.Op {
-	case "~":
-		return newValueExpression(^oprnd.Eval())
-	}
-
-	log.Panicf("Invalid unary operator '%s' for '%s' expression.",
-		e.Op, e.XMLName.Local)
-	panic("unreachable")
-}
diff --git a/nexgb/xgbgen/xml_fields.go b/nexgb/xgbgen/xml_fields.go
index 991141b..fe6c5d5 100644
--- a/nexgb/xgbgen/xml_fields.go
+++ b/nexgb/xgbgen/xml_fields.go
@@ -1,31 +1,10 @@
 package main
 
-/*
-	A series of fields should be taken as "structure contents", and *not*
-	just the single 'field' elements. Namely, 'fields' subsumes 'field'
-	elements.
-
-	More particularly, 'fields' corresponds to list, in order, of any of the
-	follow elements: pad, field, list, localfield, exprfield, valueparm
-	and switch.
-
-	Thus, the 'Field' type must contain the union of information corresponding
-	to all aforementioned fields.
-
-	This would ideally be a better job for interfaces, but I could not figure
-	out how to make them jive with Go's XML package. (And I don't really feel
-	up to type translation.)
-*/
-
 import (
 	"encoding/xml"
-	"fmt"
 	"log"
-	"strings"
 )
 
-type XMLFields []*XMLField
-
 type XMLField struct {
 	XMLName xml.Name
 
@@ -47,7 +26,7 @@ type XMLField struct {
 	ValueListName string `xml:"value-list-name,attr"`
 
 	// For 'switch' element.
-	Bitcases XMLBitcases `xml:"bitcase"`
+	Bitcases []*XMLBitcase `xml:"bitcase"`
 
 	// I don't know which elements these are for. The documentation is vague.
 	// They also seem to be completely optional.
@@ -56,41 +35,6 @@ type XMLField struct {
 	OptAltEnum string `xml:"altenum,attr"`
 }
 
-// String is for debugging purposes.
-func (f *XMLField) String() string {
-	switch f.XMLName.Local {
-	case "pad":
-		return fmt.Sprintf("pad (%d bytes)", f.Bytes)
-	case "field":
-		return fmt.Sprintf("field (type = '%s', name = '%s')", f.Type, f.Name)
-	case "list":
-		return fmt.Sprintf("list (type = '%s', name = '%s', length = '%s')",
-			f.Type, f.Name, f.Expr)
-	case "localfield":
-		return fmt.Sprintf("localfield (type = '%s', name = '%s')",
-			f.Type, f.Name)
-	case "exprfield":
-		return fmt.Sprintf("exprfield (type = '%s', name = '%s', expr = '%s')",
-			f.Type, f.Name, f.Expr)
-	case "valueparam":
-		return fmt.Sprintf("valueparam (type = '%s', name = '%s', list = '%s')",
-			f.ValueMaskType, f.ValueMaskName, f.ValueListName)
-	case "switch":
-		bitcases := make([]string, len(f.Bitcases))
-		for i, bitcase := range f.Bitcases {
-			bitcases[i] = bitcase.StringPrefix("\t")
-		}
-		return fmt.Sprintf("switch (name = '%s', expr = '%s')\n\t%s",
-			f.Name, f.Expr, strings.Join(bitcases, "\n\t"))
-	default:
-		log.Panicf("Unrecognized field element: %s", f.XMLName.Local)
-	}
-
-	panic("unreachable")
-}
-
-type XMLBitcases []*XMLBitcase
-
 // Bitcase represents a single expression followed by any number of fields.
 // Namely, if the switch's expression (all bitcases are inside a switch),
 // and'd with the bitcase's expression is equal to the bitcase expression,
@@ -100,7 +44,7 @@ type XMLBitcases []*XMLBitcase
 // it's the closest thing to a Union I can get to in Go without interfaces.
 // Would an '<expression>' tag have been too much to ask? :-(
 type XMLBitcase struct {
-	Fields XMLFields `xml:",any"`
+	Fields []*XMLField `xml:",any"`
 
 	// All the different expressions.
 	// When it comes time to choose one, use the 'Expr' method.
@@ -114,17 +58,6 @@ type XMLBitcase struct {
 	ExprPop   *XMLExpression `xml:"popcount"`
 }
 
-// StringPrefix is for debugging purposes only.
-// StringPrefix takes a string to prefix to every extra line for formatting.
-func (b *XMLBitcase) StringPrefix(prefix string) string {
-	fields := make([]string, len(b.Fields))
-	for i, field := range b.Fields {
-		fields[i] = fmt.Sprintf("%s%s", prefix, field)
-	}
-	return fmt.Sprintf("%s\n\t%s%s", b.Expr(), prefix,
-		strings.Join(fields, "\n\t"))
-}
-
 // Expr chooses the only non-nil Expr* field from Bitcase.
 // Panic if there is more than one non-nil expression.
 func (b *XMLBitcase) Expr() *XMLExpression {