diff --git a/cmd/gotype/gotype.go b/cmd/gotype/gotype.go
index 789d8223..45808087 100644
--- a/cmd/gotype/gotype.go
+++ b/cmd/gotype/gotype.go
@@ -18,6 +18,7 @@ import (
 	"runtime"
 	"time"
 
+	_ "code.google.com/p/go.tools/go/gcimporter"
 	"code.google.com/p/go.tools/go/types"
 )
 
diff --git a/cmd/vet/main.go b/cmd/vet/main.go
index 362162fa..3763cc8d 100644
--- a/cmd/vet/main.go
+++ b/cmd/vet/main.go
@@ -22,6 +22,7 @@ import (
 	"strings"
 
 	"code.google.com/p/go.tools/go/exact"
+	_ "code.google.com/p/go.tools/go/gcimporter"
 	"code.google.com/p/go.tools/go/types"
 )
 
diff --git a/go/types/exportdata.go b/go/gcimporter/exportdata.go
similarity index 93%
rename from go/types/exportdata.go
rename to go/gcimporter/exportdata.go
index 1f6a3c72..c53d18cb 100644
--- a/go/types/exportdata.go
+++ b/go/gcimporter/exportdata.go
@@ -2,9 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This file implements FindGcExportData.
+// This file implements FindExportData.
 
-package types
+package gcimporter
 
 import (
 	"bufio"
@@ -36,12 +36,12 @@ func readGopackHeader(r *bufio.Reader) (name string, size int, err error) {
 	return
 }
 
-// FindGcExportData positions the reader r at the beginning of the
+// FindExportData positions the reader r at the beginning of the
 // export data section of an underlying GC-created object/archive
 // file by reading from it. The reader must be positioned at the
 // start of the file before calling this function.
 //
-func FindGcExportData(r *bufio.Reader) (err error) {
+func FindExportData(r *bufio.Reader) (err error) {
 	// Read first line to make sure this is an object file.
 	line, err := r.ReadSlice('\n')
 	if err != nil {
diff --git a/go/types/gcimporter.go b/go/gcimporter/gcimporter.go
similarity index 70%
rename from go/types/gcimporter.go
rename to go/gcimporter/gcimporter.go
index 065b8a1b..86aba4fc 100644
--- a/go/types/gcimporter.go
+++ b/go/gcimporter/gcimporter.go
@@ -2,9 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This file implements an Importer for gc-generated object files.
-
-package types
+// Package gcimporter implements Import for gc-generated object files.
+// Importing this package installs Import as go/types.DefaultImport.
+package gcimporter
 
 import (
 	"bufio"
@@ -16,14 +16,21 @@ import (
 	"io"
 	"os"
 	"path/filepath"
-	"sort"
 	"strconv"
 	"strings"
 	"text/scanner"
 
 	"code.google.com/p/go.tools/go/exact"
+	"code.google.com/p/go.tools/go/types"
 )
 
+// debugging/development support
+const debug = false
+
+func init() {
+	types.DefaultImport = Import
+}
+
 var pkgExts = [...]string{".a", ".5", ".6", ".8"}
 
 // FindPkg returns the filename and unique package id for an import
@@ -72,7 +79,7 @@ func FindPkg(path, srcDir string) (filename, id string) {
 	return
 }
 
-// GcImportData imports a package by reading the gc-generated export data,
+// ImportData imports a package by reading the gc-generated export data,
 // adds the corresponding package object to the imports map indexed by id,
 // and returns the object.
 //
@@ -84,8 +91,8 @@ func FindPkg(path, srcDir string) (filename, id string) {
 // can be used directly, and there is no need to call this function (but
 // there is also no harm but for extra time used).
 //
-func GcImportData(imports map[string]*Package, filename, id string, data *bufio.Reader) (pkg *Package, err error) {
-	// support for gcParser error handling
+func ImportData(imports map[string]*types.Package, filename, id string, data *bufio.Reader) (pkg *types.Package, err error) {
+	// support for parser error handling
 	defer func() {
 		switch r := recover().(type) {
 		case nil:
@@ -97,21 +104,21 @@ func GcImportData(imports map[string]*Package, filename, id string, data *bufio.
 		}
 	}()
 
-	var p gcParser
+	var p parser
 	p.init(filename, id, data, imports)
 	pkg = p.parseExport()
 
 	return
 }
 
-// GcImport imports a gc-generated package given its import path, adds the
+// Import imports a gc-generated package given its import path, adds the
 // corresponding package object to the imports map, and returns the object.
 // Local import paths are interpreted relative to the current working directory.
 // The imports map must contains all packages already imported.
 //
-func GcImport(imports map[string]*Package, path string) (pkg *Package, err error) {
+func Import(imports map[string]*types.Package, path string) (pkg *types.Package, err error) {
 	if path == "unsafe" {
-		return Unsafe, nil
+		return types.Unsafe, nil
 	}
 
 	srcDir := "."
@@ -129,7 +136,7 @@ func GcImport(imports map[string]*Package, path string) (pkg *Package, err error
 	}
 
 	// no need to re-import if the package was imported completely before
-	if pkg = imports[id]; pkg != nil && pkg.complete {
+	if pkg = imports[id]; pkg != nil && pkg.Complete() {
 		return
 	}
 
@@ -147,17 +154,17 @@ func GcImport(imports map[string]*Package, path string) (pkg *Package, err error
 	}()
 
 	buf := bufio.NewReader(f)
-	if err = FindGcExportData(buf); err != nil {
+	if err = FindExportData(buf); err != nil {
 		return
 	}
 
-	pkg, err = GcImportData(imports, filename, id, buf)
+	pkg, err = ImportData(imports, filename, id, buf)
 
 	return
 }
 
 // ----------------------------------------------------------------------------
-// gcParser
+// Parser
 
 // TODO(gri) Imported objects don't have position information.
 //           Ideally use the debug table line info; alternatively
@@ -165,17 +172,17 @@ func GcImport(imports map[string]*Package, path string) (pkg *Package, err error
 //           import). That way error messages referring to imported
 //           objects can print meaningful information.
 
-// gcParser parses the exports inside a gc compiler-produced
+// parser parses the exports inside a gc compiler-produced
 // object/archive file and populates its scope with the results.
-type gcParser struct {
+type parser struct {
 	scanner scanner.Scanner
-	tok     rune                // current token
-	lit     string              // literal string; only valid for Ident, Int, String tokens
-	id      string              // package id of imported package
-	imports map[string]*Package // package id -> package object
+	tok     rune                      // current token
+	lit     string                    // literal string; only valid for Ident, Int, String tokens
+	id      string                    // package id of imported package
+	imports map[string]*types.Package // package id -> package object
 }
 
-func (p *gcParser) init(filename, id string, src io.Reader, imports map[string]*Package) {
+func (p *parser) init(filename, id string, src io.Reader, imports map[string]*types.Package) {
 	p.scanner.Init(src)
 	p.scanner.Error = func(_ *scanner.Scanner, msg string) { p.error(msg) }
 	p.scanner.Mode = scanner.ScanIdents | scanner.ScanInts | scanner.ScanChars | scanner.ScanStrings | scanner.ScanComments | scanner.SkipComments
@@ -184,18 +191,17 @@ func (p *gcParser) init(filename, id string, src io.Reader, imports map[string]*
 	p.next()
 	p.id = id
 	p.imports = imports
-	// leave for debugging
-	if false {
+	if debug {
 		// check consistency of imports map
 		for _, pkg := range imports {
-			if pkg.name == "" {
-				fmt.Printf("no package name for %s\n", pkg.path)
+			if pkg.Name() == "" {
+				fmt.Printf("no package name for %s\n", pkg.Path())
 			}
 		}
 	}
 }
 
-func (p *gcParser) next() {
+func (p *parser) next() {
 	p.tok = p.scanner.Scan()
 	switch p.tok {
 	case scanner.Ident, scanner.Int, scanner.Char, scanner.String, '·':
@@ -203,54 +209,20 @@ func (p *gcParser) next() {
 	default:
 		p.lit = ""
 	}
-	// leave for debugging
-	if false {
+	if debug {
 		fmt.Printf("%s: %q -> %q\n", scanner.TokenString(p.tok), p.scanner.TokenText(), p.lit)
 	}
 }
 
-func declConst(pkg *Package, name string) *Const {
-	// the constant may have been imported before - if it exists
-	// already in the respective scope, return that constant
-	scope := pkg.scope
+func declTypeName(pkg *types.Package, name string) *types.TypeName {
+	scope := pkg.Scope()
 	if obj := scope.Lookup(name); obj != nil {
-		return obj.(*Const)
+		return obj.(*types.TypeName)
 	}
-	// otherwise create a new constant and insert it into the scope
-	obj := NewConst(token.NoPos, pkg, name, nil, nil)
-	scope.Insert(obj)
-	return obj
-}
-
-func declTypeName(pkg *Package, name string) *TypeName {
-	scope := pkg.scope
-	if obj := scope.Lookup(name); obj != nil {
-		return obj.(*TypeName)
-	}
-	obj := NewTypeName(token.NoPos, pkg, name, nil)
+	obj := types.NewTypeName(token.NoPos, pkg, name, nil)
 	// a named type may be referred to before the underlying type
 	// is known - set it up
-	obj.typ = &Named{obj: obj}
-	scope.Insert(obj)
-	return obj
-}
-
-func declVar(pkg *Package, name string) *Var {
-	scope := pkg.scope
-	if obj := scope.Lookup(name); obj != nil {
-		return obj.(*Var)
-	}
-	obj := NewVar(token.NoPos, pkg, name, nil)
-	scope.Insert(obj)
-	return obj
-}
-
-func declFunc(pkg *Package, name string) *Func {
-	scope := pkg.scope
-	if obj := scope.Lookup(name); obj != nil {
-		return obj.(*Func)
-	}
-	obj := NewFunc(token.NoPos, pkg, name, nil)
+	types.NewNamed(obj, nil, nil)
 	scope.Insert(obj)
 	return obj
 }
@@ -268,7 +240,7 @@ func (e importError) Error() string {
 	return fmt.Sprintf("import error %s (byte offset = %d): %s", e.pos, e.pos.Offset, e.err)
 }
 
-func (p *gcParser) error(err interface{}) {
+func (p *parser) error(err interface{}) {
 	if s, ok := err.(string); ok {
 		err = errors.New(s)
 	}
@@ -276,11 +248,11 @@ func (p *gcParser) error(err interface{}) {
 	panic(importError{p.scanner.Pos(), err.(error)})
 }
 
-func (p *gcParser) errorf(format string, args ...interface{}) {
+func (p *parser) errorf(format string, args ...interface{}) {
 	p.error(fmt.Sprintf(format, args...))
 }
 
-func (p *gcParser) expect(tok rune) string {
+func (p *parser) expect(tok rune) string {
 	lit := p.lit
 	if p.tok != tok {
 		p.errorf("expected %s, got %s (%s)", scanner.TokenString(tok), scanner.TokenString(p.tok), lit)
@@ -289,7 +261,7 @@ func (p *gcParser) expect(tok rune) string {
 	return lit
 }
 
-func (p *gcParser) expectSpecial(tok string) {
+func (p *parser) expectSpecial(tok string) {
 	sep := 'x' // not white space
 	i := 0
 	for i < len(tok) && p.tok == rune(tok[i]) && sep > ' ' {
@@ -302,7 +274,7 @@ func (p *gcParser) expectSpecial(tok string) {
 	}
 }
 
-func (p *gcParser) expectKeyword(keyword string) {
+func (p *parser) expectKeyword(keyword string) {
 	lit := p.expect(scanner.Ident)
 	if lit != keyword {
 		p.errorf("expected keyword %s, got %q", keyword, lit)
@@ -314,7 +286,7 @@ func (p *gcParser) expectKeyword(keyword string) {
 
 // PackageId = string_lit .
 //
-func (p *gcParser) parsePackageId() string {
+func (p *parser) parsePackageId() string {
 	id, err := strconv.Unquote(p.expect(scanner.String))
 	if err != nil {
 		p.error(err)
@@ -329,12 +301,12 @@ func (p *gcParser) parsePackageId() string {
 
 // PackageName = ident .
 //
-func (p *gcParser) parsePackageName() string {
+func (p *parser) parsePackageName() string {
 	return p.expect(scanner.Ident)
 }
 
 // dotIdentifier = ( ident | '·' ) { ident | int | '·' } .
-func (p *gcParser) parseDotIdent() string {
+func (p *parser) parseDotIdent() string {
 	ident := ""
 	if p.tok != scanner.Int {
 		sep := 'x' // not white space
@@ -352,7 +324,7 @@ func (p *gcParser) parseDotIdent() string {
 
 // QualifiedName = "@" PackageId "." ( "?" | dotIdentifier ) .
 //
-func (p *gcParser) parseQualifiedName() (id, name string) {
+func (p *parser) parseQualifiedName() (id, name string) {
 	p.expect('@')
 	id = p.parsePackageId()
 	p.expect('.')
@@ -369,23 +341,23 @@ func (p *gcParser) parseQualifiedName() (id, name string) {
 // not found but we have a package name, create the package and
 // add it to the p.imports map.
 //
-func (p *gcParser) getPkg(id, name string) *Package {
+func (p *parser) getPkg(id, name string) *types.Package {
 	// package unsafe is not in the imports map - handle explicitly
 	if id == "unsafe" {
-		return Unsafe
+		return types.Unsafe
 	}
 	pkg := p.imports[id]
 	if pkg == nil && name != "" {
-		pkg = NewPackage(id, name, NewScope(nil))
+		pkg = types.NewPackage(id, name, types.NewScope(nil))
 		p.imports[id] = pkg
 	}
 	return pkg
 }
 
 // parseExportedName is like parseQualifiedName, but
-// the package id is resolved to an imported *Package.
+// the package id is resolved to an imported *types.Package.
 //
-func (p *gcParser) parseExportedName() (pkg *Package, name string) {
+func (p *parser) parseExportedName() (pkg *types.Package, name string) {
 	id, name := p.parseQualifiedName()
 	pkg = p.getPkg(id, "")
 	if pkg == nil {
@@ -399,11 +371,11 @@ func (p *gcParser) parseExportedName() (pkg *Package, name string) {
 
 // BasicType = identifier .
 //
-func (p *gcParser) parseBasicType() Type {
+func (p *parser) parseBasicType() types.Type {
 	id := p.expect(scanner.Ident)
-	obj := Universe.Lookup(id)
-	if obj, ok := obj.(*TypeName); ok {
-		return obj.typ
+	obj := types.Universe.Lookup(id)
+	if obj, ok := obj.(*types.TypeName); ok {
+		return obj.Type()
 	}
 	p.errorf("not a basic type: %s", id)
 	return nil
@@ -411,7 +383,7 @@ func (p *gcParser) parseBasicType() Type {
 
 // ArrayType = "[" int_lit "]" Type .
 //
-func (p *gcParser) parseArrayType() Type {
+func (p *parser) parseArrayType() types.Type {
 	// "[" already consumed and lookahead known not to be "]"
 	lit := p.expect(scanner.Int)
 	p.expect(']')
@@ -420,18 +392,18 @@ func (p *gcParser) parseArrayType() Type {
 	if err != nil {
 		p.error(err)
 	}
-	return &Array{len: n, elem: elem}
+	return types.NewArray(elem, n)
 }
 
 // MapType = "map" "[" Type "]" Type .
 //
-func (p *gcParser) parseMapType() Type {
+func (p *parser) parseMapType() types.Type {
 	p.expectKeyword("map")
 	p.expect('[')
 	key := p.parseType()
 	p.expect(']')
 	elem := p.parseType()
-	return &Map{key: key, elem: elem}
+	return types.NewMap(key, elem)
 }
 
 // Name = identifier | "?" | QualifiedName .
@@ -444,7 +416,7 @@ func (p *gcParser) parseMapType() Type {
 // we cannot create a real package because we don't have a package name.
 // For non-qualified names, the returned package is the imported package.
 //
-func (p *gcParser) parseName(materializePkg bool) (pkg *Package, name string) {
+func (p *parser) parseName(materializePkg bool) (pkg *types.Package, name string) {
 	switch p.tok {
 	case scanner.Ident:
 		pkg = p.imports[p.id]
@@ -463,7 +435,7 @@ func (p *gcParser) parseName(materializePkg bool) (pkg *Package, name string) {
 			// doesn't exist yet, create a fake package instead
 			pkg = p.getPkg(id, "")
 			if pkg == nil {
-				pkg = &Package{path: id}
+				pkg = types.NewPackage(id, "", nil)
 			}
 		}
 	default:
@@ -472,21 +444,29 @@ func (p *gcParser) parseName(materializePkg bool) (pkg *Package, name string) {
 	return
 }
 
+func deref(typ types.Type) types.Type {
+	if p, _ := typ.(*types.Pointer); p != nil {
+		return p.Elem()
+	}
+	return typ
+}
+
 // Field = Name Type [ string_lit ] .
 //
-func (p *gcParser) parseField() (*Var, string) {
+func (p *parser) parseField() (*types.Var, string) {
 	pkg, name := p.parseName(true)
 	typ := p.parseType()
 	anonymous := false
 	if name == "" {
 		// anonymous field - typ must be T or *T and T must be a type name
-		switch typ, _ := deref(typ); typ := typ.(type) {
-		case *Basic: // basic types are named types
+		switch typ := deref(typ).(type) {
+		case *types.Basic: // basic types are named types
 			pkg = nil
-			name = typ.name
-		case *Named:
-			pkg = typ.obj.pkg // TODO(gri) is this still correct?
-			name = typ.obj.name
+			name = typ.Name()
+		case *types.Named:
+			obj := typ.Obj()
+			pkg = obj.Pkg() // TODO(gri) is this still correct?
+			name = obj.Name()
 		default:
 			p.errorf("anonymous field expected")
 		}
@@ -496,19 +476,18 @@ func (p *gcParser) parseField() (*Var, string) {
 	if p.tok == scanner.String {
 		tag = p.expect(scanner.String)
 	}
-	return NewField(token.NoPos, pkg, name, typ, anonymous), tag
+	return types.NewField(token.NoPos, pkg, name, typ, anonymous), tag
 }
 
 // StructType = "struct" "{" [ FieldList ] "}" .
 // FieldList  = Field { ";" Field } .
 //
-func (p *gcParser) parseStructType() Type {
-	var fields []*Var
+func (p *parser) parseStructType() types.Type {
+	var fields []*types.Var
 	var tags []string
 
 	p.expectKeyword("struct")
 	p.expect('{')
-	var fset objset
 	for i := 0; p.tok != '}'; i++ {
 		if i > 0 {
 			p.expect(';')
@@ -520,26 +499,16 @@ func (p *gcParser) parseStructType() Type {
 		if tags != nil {
 			tags = append(tags, tag)
 		}
-		if fld.name != "_" {
-			if alt := fset.insert(fld); alt != nil {
-				pname := "<no pkg name>"
-				if pkg := alt.Pkg(); pkg != nil {
-					pname = pkg.name
-				}
-				p.errorf("multiple fields named %s.%s", pname, alt.Name())
-				continue
-			}
-		}
 		fields = append(fields, fld)
 	}
 	p.expect('}')
 
-	return &Struct{fields: fields, tags: tags}
+	return types.NewStruct(fields, tags)
 }
 
 // Parameter = ( identifier | "?" ) [ "..." ] Type [ string_lit ] .
 //
-func (p *gcParser) parseParameter() (par *Var, isVariadic bool) {
+func (p *parser) parseParameter() (par *types.Var, isVariadic bool) {
 	_, name := p.parseName(false)
 	if name == "" {
 		name = "_" // cannot access unnamed identifiers
@@ -550,21 +519,21 @@ func (p *gcParser) parseParameter() (par *Var, isVariadic bool) {
 	}
 	typ := p.parseType()
 	if isVariadic {
-		typ = &Slice{elem: typ}
+		typ = types.NewSlice(typ)
 	}
 	// ignore argument tag (e.g. "noescape")
 	if p.tok == scanner.String {
 		p.next()
 	}
 	// TODO(gri) should we provide a package?
-	par = NewVar(token.NoPos, nil, name, typ)
+	par = types.NewVar(token.NoPos, nil, name, typ)
 	return
 }
 
 // Parameters    = "(" [ ParameterList ] ")" .
 // ParameterList = { Parameter "," } Parameter .
 //
-func (p *gcParser) parseParameters() (list []*Var, isVariadic bool) {
+func (p *parser) parseParameters() (list []*types.Var, isVariadic bool) {
 	p.expect('(')
 	for p.tok != ')' {
 		if len(list) > 0 {
@@ -587,11 +556,11 @@ func (p *gcParser) parseParameters() (list []*Var, isVariadic bool) {
 // Signature = Parameters [ Result ] .
 // Result    = Type | Parameters .
 //
-func (p *gcParser) parseSignature() *Signature {
+func (p *parser) parseSignature(recv *types.Var) *types.Signature {
 	params, isVariadic := p.parseParameters()
 
 	// optional result type
-	var results []*Var
+	var results []*types.Var
 	if p.tok == '(' {
 		var variadic bool
 		results, variadic = p.parseParameters()
@@ -600,7 +569,7 @@ func (p *gcParser) parseSignature() *Signature {
 		}
 	}
 
-	return &Signature{params: NewTuple(params...), results: NewTuple(results...), isVariadic: isVariadic}
+	return types.NewSignature(nil, recv, types.NewTuple(params...), types.NewTuple(results...), isVariadic)
 }
 
 // InterfaceType = "interface" "{" [ MethodList ] "}" .
@@ -611,40 +580,27 @@ func (p *gcParser) parseSignature() *Signature {
 // by the compiler and thus embedded interfaces are never
 // visible in the export data.
 //
-func (p *gcParser) parseInterfaceType() Type {
-	typ := new(Interface)
-	var methods []*Func
+func (p *parser) parseInterfaceType() types.Type {
+	var methods []*types.Func
 
 	p.expectKeyword("interface")
 	p.expect('{')
-	var mset objset
 	for i := 0; p.tok != '}'; i++ {
 		if i > 0 {
 			p.expect(';')
 		}
 		pkg, name := p.parseName(true)
-		sig := p.parseSignature()
-		// TODO(gri) Ideally, we should use a named type here instead of
-		// typ, for less verbose printing of interface method signatures.
-		sig.recv = NewVar(token.NoPos, pkg, "", typ)
-		m := NewFunc(token.NoPos, pkg, name, sig)
-		if alt := mset.insert(m); alt != nil {
-			p.errorf("multiple methods named %s.%s", alt.Pkg().name, alt.Name())
-			continue
-		}
-		methods = append(methods, m)
+		sig := p.parseSignature(nil)
+		methods = append(methods, types.NewFunc(token.NoPos, pkg, name, sig))
 	}
 	p.expect('}')
 
-	sort.Sort(byUniqueMethodName(methods))
-	typ.methods = methods
-	typ.allMethods = methods // ok to share underlying array since we are not changing methods
-	return typ
+	return types.NewInterface(methods, nil)
 }
 
 // ChanType = ( "chan" [ "<-" ] | "<-" "chan" ) Type .
 //
-func (p *gcParser) parseChanType() Type {
+func (p *parser) parseChanType() types.Type {
 	dir := ast.SEND | ast.RECV
 	if p.tok == scanner.Ident {
 		p.expectKeyword("chan")
@@ -658,7 +614,7 @@ func (p *gcParser) parseChanType() Type {
 		dir = ast.RECV
 	}
 	elem := p.parseType()
-	return &Chan{dir: dir, elem: elem}
+	return types.NewChan(dir, elem)
 }
 
 // Type =
@@ -672,7 +628,7 @@ func (p *gcParser) parseChanType() Type {
 // PointerType = "*" Type .
 // FuncType    = "func" Signature .
 //
-func (p *gcParser) parseType() Type {
+func (p *parser) parseType() types.Type {
 	switch p.tok {
 	case scanner.Ident:
 		switch p.lit {
@@ -683,7 +639,7 @@ func (p *gcParser) parseType() Type {
 		case "func":
 			// FuncType
 			p.next()
-			return p.parseSignature()
+			return p.parseSignature(nil)
 		case "interface":
 			return p.parseInterfaceType()
 		case "map":
@@ -694,19 +650,19 @@ func (p *gcParser) parseType() Type {
 	case '@':
 		// TypeName
 		pkg, name := p.parseExportedName()
-		return declTypeName(pkg, name).typ
+		return declTypeName(pkg, name).Type()
 	case '[':
 		p.next() // look ahead
 		if p.tok == ']' {
 			// SliceType
 			p.next()
-			return &Slice{elem: p.parseType()}
+			return types.NewSlice(p.parseType())
 		}
 		return p.parseArrayType()
 	case '*':
 		// PointerType
 		p.next()
-		return &Pointer{base: p.parseType()}
+		return types.NewPointer(p.parseType())
 	case '<':
 		return p.parseChanType()
 	case '(':
@@ -725,7 +681,7 @@ func (p *gcParser) parseType() Type {
 
 // ImportDecl = "import" PackageName PackageId .
 //
-func (p *gcParser) parseImportDecl() {
+func (p *parser) parseImportDecl() {
 	p.expectKeyword("import")
 	name := p.parsePackageName()
 	p.getPkg(p.parsePackageId(), name)
@@ -733,7 +689,7 @@ func (p *gcParser) parseImportDecl() {
 
 // int_lit = [ "+" | "-" ] { "0" ... "9" } .
 //
-func (p *gcParser) parseInt() string {
+func (p *parser) parseInt() string {
 	s := ""
 	switch p.tok {
 	case '-':
@@ -747,12 +703,12 @@ func (p *gcParser) parseInt() string {
 
 // number = int_lit [ "p" int_lit ] .
 //
-func (p *gcParser) parseNumber() (x operand) {
-	x.mode = constant
-
+func (p *parser) parseNumber() (typ *types.Basic, val exact.Value) {
 	// mantissa
 	mant := exact.MakeFromLiteral(p.parseInt(), token.INT)
-	assert(mant != nil)
+	if mant == nil {
+		panic("invalid mantissa")
+	}
 
 	if p.lit == "p" {
 		// exponent (base 2)
@@ -764,20 +720,20 @@ func (p *gcParser) parseNumber() (x operand) {
 		if exp < 0 {
 			denom := exact.MakeInt64(1)
 			denom = exact.Shift(denom, token.SHL, uint(-exp))
-			x.typ = Typ[UntypedFloat]
-			x.val = exact.BinaryOp(mant, token.QUO, denom)
+			typ = types.Typ[types.UntypedFloat]
+			val = exact.BinaryOp(mant, token.QUO, denom)
 			return
 		}
 		if exp > 0 {
 			mant = exact.Shift(mant, token.SHL, uint(exp))
 		}
-		x.typ = Typ[UntypedFloat]
-		x.val = mant
+		typ = types.Typ[types.UntypedFloat]
+		val = mant
 		return
 	}
 
-	x.typ = Typ[UntypedInt]
-	x.val = mant
+	typ = types.Typ[types.UntypedInt]
+	val = mant
 	return
 }
 
@@ -788,28 +744,31 @@ func (p *gcParser) parseNumber() (x operand) {
 // rune_lit    = "(" int_lit "+" int_lit ")" .
 // string_lit  = `"` { unicode_char } `"` .
 //
-func (p *gcParser) parseConstDecl() {
+func (p *parser) parseConstDecl() {
 	p.expectKeyword("const")
 	pkg, name := p.parseExportedName()
-	obj := declConst(pkg, name)
-	var x operand
+
+	var typ0 types.Type
 	if p.tok != '=' {
-		obj.typ = p.parseType()
+		typ0 = p.parseType()
 	}
+
 	p.expect('=')
+	var typ types.Type
+	var val exact.Value
 	switch p.tok {
 	case scanner.Ident:
 		// bool_lit
 		if p.lit != "true" && p.lit != "false" {
 			p.error("expected true or false")
 		}
-		x.typ = Typ[UntypedBool]
-		x.val = exact.MakeBool(p.lit == "true")
+		typ = types.Typ[types.UntypedBool]
+		val = exact.MakeBool(p.lit == "true")
 		p.next()
 
 	case '-', scanner.Int:
 		// int_lit
-		x = p.parseNumber()
+		typ, val = p.parseNumber()
 
 	case '(':
 		// complex_lit or rune_lit
@@ -817,44 +776,45 @@ func (p *gcParser) parseConstDecl() {
 		if p.tok == scanner.Char {
 			p.next()
 			p.expect('+')
-			x = p.parseNumber()
-			x.typ = Typ[UntypedRune]
+			typ = types.Typ[types.UntypedRune]
+			_, val = p.parseNumber()
 			p.expect(')')
 			break
 		}
-		re := p.parseNumber()
+		_, re := p.parseNumber()
 		p.expect('+')
-		im := p.parseNumber()
+		_, im := p.parseNumber()
 		p.expectKeyword("i")
 		p.expect(')')
-		x.typ = Typ[UntypedComplex]
-		// TODO(gri) fix this
-		_, _ = re, im
-		x.val = exact.MakeInt64(0)
+		typ = types.Typ[types.UntypedComplex]
+		val = exact.BinaryOp(re, token.ADD, exact.MakeImag(im))
 
 	case scanner.Char:
 		// rune_lit
-		x.setConst(token.CHAR, p.lit)
+		typ = types.Typ[types.UntypedRune]
+		val = exact.MakeFromLiteral(p.lit, token.CHAR)
 		p.next()
 
 	case scanner.String:
 		// string_lit
-		x.setConst(token.STRING, p.lit)
+		typ = types.Typ[types.UntypedString]
+		val = exact.MakeFromLiteral(p.lit, token.STRING)
 		p.next()
 
 	default:
 		p.errorf("expected literal got %s", scanner.TokenString(p.tok))
 	}
-	if obj.typ == nil {
-		obj.typ = x.typ
+
+	if typ0 == nil {
+		typ0 = typ
 	}
-	assert(x.val != nil)
-	obj.val = x.val
+
+	pkg.Scope().Insert(types.NewConst(token.NoPos, pkg, name, typ0, val))
 }
 
 // TypeDecl = "type" ExportedName Type .
 //
-func (p *gcParser) parseTypeDecl() {
+func (p *parser) parseTypeDecl() {
 	p.expectKeyword("type")
 	pkg, name := p.parseExportedName()
 	obj := declTypeName(pkg, name)
@@ -866,26 +826,25 @@ func (p *gcParser) parseTypeDecl() {
 	// a given type declaration.
 	typ := p.parseType()
 
-	if name := obj.typ.(*Named); name.underlying == nil {
-		name.underlying = typ
-		name.complete = true
+	if name := obj.Type().(*types.Named); name.Underlying() == nil {
+		name.SetUnderlying(typ)
 	}
 }
 
 // VarDecl = "var" ExportedName Type .
 //
-func (p *gcParser) parseVarDecl() {
+func (p *parser) parseVarDecl() {
 	p.expectKeyword("var")
 	pkg, name := p.parseExportedName()
-	obj := declVar(pkg, name)
-	obj.typ = p.parseType()
+	typ := p.parseType()
+	pkg.Scope().Insert(types.NewVar(token.NoPos, pkg, name, typ))
 }
 
 // Func = Signature [ Body ] .
 // Body = "{" ... "}" .
 //
-func (p *gcParser) parseFunc() *Signature {
-	sig := p.parseSignature()
+func (p *parser) parseFunc(recv *types.Var) *types.Signature {
+	sig := p.parseSignature(recv)
 	if p.tok == '{' {
 		p.next()
 		for i := 1; i > 0; p.next() {
@@ -903,44 +862,37 @@ func (p *gcParser) parseFunc() *Signature {
 // MethodDecl = "func" Receiver Name Func .
 // Receiver   = "(" ( identifier | "?" ) [ "*" ] ExportedName ")" .
 //
-func (p *gcParser) parseMethodDecl() {
+func (p *parser) parseMethodDecl() {
 	// "func" already consumed
 	p.expect('(')
 	recv, _ := p.parseParameter() // receiver
 	p.expect(')')
 
 	// determine receiver base type object
-	typ := recv.typ
-	if ptr, ok := typ.(*Pointer); ok {
-		typ = ptr.base
-	}
-	base := typ.(*Named)
+	base := deref(recv.Type()).(*types.Named)
 
 	// parse method name, signature, and possibly inlined body
 	pkg, name := p.parseName(true)
-	sig := p.parseFunc()
-	sig.recv = recv
+	sig := p.parseFunc(recv)
 
 	// add method to type unless type was imported before
 	// and method exists already
-	// TODO(gri) This is a quadratic algorithm - ok for now because method counts are small.
-	if _, m := lookupMethod(base.methods, pkg, name); m == nil {
-		base.methods = append(base.methods, NewFunc(token.NoPos, pkg, name, sig))
-	}
+	// TODO(gri) This leads to a quadratic algorithm - ok for now because method counts are small.
+	base.AddMethod(types.NewFunc(token.NoPos, pkg, name, sig))
 }
 
 // FuncDecl = "func" ExportedName Func .
 //
-func (p *gcParser) parseFuncDecl() {
+func (p *parser) parseFuncDecl() {
 	// "func" already consumed
 	pkg, name := p.parseExportedName()
-	typ := p.parseFunc()
-	declFunc(pkg, name).typ = typ
+	typ := p.parseFunc(nil)
+	pkg.Scope().Insert(types.NewFunc(token.NoPos, pkg, name, typ))
 }
 
 // Decl = [ ImportDecl | ConstDecl | TypeDecl | VarDecl | FuncDecl | MethodDecl ] "\n" .
 //
-func (p *gcParser) parseDecl() {
+func (p *parser) parseDecl() {
 	switch p.lit {
 	case "import":
 		p.parseImportDecl()
@@ -967,7 +919,7 @@ func (p *gcParser) parseDecl() {
 // Export        = "PackageClause { Decl } "$$" .
 // PackageClause = "package" PackageName [ "safe" ] "\n" .
 //
-func (p *gcParser) parseExport() *Package {
+func (p *parser) parseExport() *types.Package {
 	p.expectKeyword("package")
 	name := p.parsePackageName()
 	if p.tok != '\n' {
@@ -995,7 +947,7 @@ func (p *gcParser) parseExport() *Package {
 	}
 
 	// package was imported completely and without errors
-	pkg.complete = true
+	pkg.MarkComplete()
 
 	return pkg
 }
diff --git a/go/types/gcimporter_test.go b/go/gcimporter/gcimporter_test.go
similarity index 76%
rename from go/types/gcimporter_test.go
rename to go/gcimporter/gcimporter_test.go
index 67f5dc14..11a53c51 100644
--- a/go/types/gcimporter_test.go
+++ b/go/gcimporter/gcimporter_test.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package types
+package gcimporter
 
 import (
 	"go/build"
@@ -14,6 +14,8 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"code.google.com/p/go.tools/go/types"
 )
 
 var gcPath string // Go compiler path
@@ -50,11 +52,11 @@ func compile(t *testing.T, dirname, filename string) string {
 
 // Use the same global imports map for all tests. The effect is
 // as if all tested packages were imported into a single package.
-var imports = make(map[string]*Package)
+var imports = make(map[string]*types.Package)
 
 func testPath(t *testing.T, path string) bool {
 	t0 := time.Now()
-	_, err := GcImport(imports, path)
+	_, err := Import(imports, path)
 	if err != nil {
 		t.Errorf("testPath(%s): %s", path, err)
 		return false
@@ -94,7 +96,12 @@ func testDir(t *testing.T, dir string, endTime time.Time) (nimports int) {
 	return
 }
 
-func TestGcImport(t *testing.T) {
+func TestImport(t *testing.T) {
+	// This package does not handle gccgo export data.
+	if runtime.Compiler == "gccgo" {
+		return
+	}
+
 	// On cross-compile builds, the path will not exist.
 	// Need to use GOHOSTOS, which is not available.
 	if _, err := os.Stat(gcPath); err != nil {
@@ -125,8 +132,8 @@ var importedObjectTests = []struct {
 	// TODO(gri) add more tests
 }
 
-func TestGcImportedTypes(t *testing.T) {
-	// This package does not yet know how to read gccgo export data.
+func TestImportedTypes(t *testing.T) {
+	// This package does not handle gccgo export data.
 	if runtime.Compiler == "gccgo" {
 		return
 	}
@@ -138,13 +145,13 @@ func TestGcImportedTypes(t *testing.T) {
 		importPath := s[0]
 		objName := s[1]
 
-		pkg, err := GcImport(imports, importPath)
+		pkg, err := Import(imports, importPath)
 		if err != nil {
 			t.Error(err)
 			continue
 		}
 
-		obj := pkg.scope.Lookup(objName)
+		obj := pkg.Scope().Lookup(objName)
 		if obj == nil {
 			t.Errorf("%s: object not found", test.name)
 			continue
@@ -156,3 +163,32 @@ func TestGcImportedTypes(t *testing.T) {
 		}
 	}
 }
+
+func TestIssue5815(t *testing.T) {
+	// This package does not handle gccgo export data.
+	if runtime.Compiler == "gccgo" {
+		return
+	}
+
+	pkg, err := Import(make(map[string]*types.Package), "strings")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	scope := pkg.Scope()
+	for _, name := range scope.Names() {
+		obj := scope.Lookup(name)
+		if obj.Pkg() == nil {
+			t.Errorf("no pkg for %s", obj)
+		}
+		if tname, _ := obj.(*types.TypeName); tname != nil {
+			named := tname.Type().(*types.Named)
+			for i := 0; i < named.NumMethods(); i++ {
+				m := named.Method(i)
+				if m.Pkg() == nil {
+					t.Errorf("no pkg for %s", m)
+				}
+			}
+		}
+	}
+}
diff --git a/go/types/testdata/exports.go b/go/gcimporter/testdata/exports.go
similarity index 100%
rename from go/types/testdata/exports.go
rename to go/gcimporter/testdata/exports.go
diff --git a/go/types/api.go b/go/types/api.go
index dbf145ec..6eb10340 100644
--- a/go/types/api.go
+++ b/go/types/api.go
@@ -59,6 +59,19 @@ func (err Error) Error() string {
 	return fmt.Sprintf("%s: %s", err.Fset.Position(err.Pos), err.Msg)
 }
 
+// An importer resolves import paths to Packages.
+// The imports map records packages already known,
+// indexed by package path. The type-checker
+// will invoke Import with Config.Packages.
+// An importer must determine the canonical package path and
+// check imports to see if it is already present in the map.
+// If so, the Importer can return the map entry.  Otherwise,
+// the importer must load the package data for the given path
+// into a new *Package, record it in imports map, and return
+// the package.
+// TODO(gri) Need to be clearer about requirements of completeness.
+type Importer func(map[string]*Package, string) (*Package, error)
+
 // A Config specifies the configuration for type checking.
 // The zero value for Config is a ready-to-use default configuration.
 type Config struct {
@@ -85,24 +98,22 @@ type Config struct {
 	Error func(err error)
 
 	// If Import != nil, it is called for each imported package.
-	// Otherwise, GcImporter is called.
-	// An importer resolves import paths to Packages.
-	// The imports map records packages already known,
-	// indexed by canonical package path. The type-checker will
-	// invoke Import with Config.Packages.
-	// An importer must determine the canonical package path and
-	// check imports to see if it is already present in the map.
-	// If so, the Importer can return the map entry.  Otherwise,
-	// the importer must load the package data for the given path
-	// into a new *Package, record it in imports map, and return
-	// the package.
-	Import func(imports map[string]*Package, path string) (pkg *Package, err error)
+	// Otherwise, DefaultImport is called.
+	Import Importer
 
 	// If Sizes != nil, it provides the sizing functions for package unsafe.
 	// Otherwise &StdSize{WordSize: 8, MaxAlign: 8} is used instead.
 	Sizes Sizes
 }
 
+// DefaultImport is the default importer invoked if Config.Import == nil.
+// The declaration:
+//
+//	import _ "code.google.com/p/go.tools/go/gcimporter"
+//
+// in a client of go/types will initialize DefaultImport to gcimporter.Import.
+var DefaultImport Importer
+
 // Info holds result type information for a type-checked package.
 // Only the information for which a map is provided is collected.
 // If the package has type errors, the collected information may
diff --git a/go/types/api_test.go b/go/types/api_test.go
index 8c74d6b0..f7fb33e6 100644
--- a/go/types/api_test.go
+++ b/go/types/api_test.go
@@ -4,7 +4,7 @@
 
 // TODO(gri) This file needs to be expanded significantly.
 
-package types
+package types_test
 
 import (
 	"bytes"
@@ -13,6 +13,9 @@ import (
 	"go/token"
 	"strings"
 	"testing"
+
+	_ "code.google.com/p/go.tools/go/gcimporter"
+	. "code.google.com/p/go.tools/go/types"
 )
 
 func pkgFor(path, source string, info *Info) (*Package, error) {
@@ -70,7 +73,7 @@ func TestCommaOkTypes(t *testing.T) {
 		// look for comma-ok expression type
 		var typ Type
 		for e, t := range info.Types {
-			if exprString(e) == test.expr {
+			if ExprString(e) == test.expr {
 				typ = t
 				break
 			}
@@ -214,10 +217,10 @@ func initString(init *Initializer) string {
 		if i > 0 {
 			buf.WriteString(", ")
 		}
-		buf.WriteString(lhs.name)
+		buf.WriteString(lhs.Name())
 	}
 	buf.WriteString(" = ")
-	writeExpr(&buf, init.Rhs)
+	WriteExpr(&buf, init.Rhs)
 	return buf.String()
 }
 
diff --git a/go/types/builtins_test.go b/go/types/builtins_test.go
index af1ad9e6..63295226 100644
--- a/go/types/builtins_test.go
+++ b/go/types/builtins_test.go
@@ -2,123 +2,129 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package types
+package types_test
 
 import (
 	"fmt"
 	"go/ast"
 	"go/parser"
 	"testing"
+
+	_ "code.google.com/p/go.tools/go/gcimporter"
+	. "code.google.com/p/go.tools/go/types"
 )
 
 var builtinCalls = []struct {
-	id  builtinId
-	src string
-	sig string
+	name, src, sig string
 }{
-	{_Append, `var s []int; _ = append(s)`, `func([]int, ...int) []int`},
-	{_Append, `var s []int; _ = append(s, 0)`, `func([]int, ...int) []int`},
-	{_Append, `var s []int; _ = (append)(s, 0)`, `func([]int, ...int) []int`},
-	{_Append, `var s []byte; _ = ((append))(s, 0)`, `func([]byte, ...byte) []byte`},
+	{"append", `var s []int; _ = append(s)`, `func([]int, ...int) []int`},
+	{"append", `var s []int; _ = append(s, 0)`, `func([]int, ...int) []int`},
+	{"append", `var s []int; _ = (append)(s, 0)`, `func([]int, ...int) []int`},
+	{"append", `var s []byte; _ = ((append))(s, 0)`, `func([]byte, ...byte) []byte`},
 	// Note that ...uint8 (instead of ..byte) appears below because that is the type
 	// that corresponds to Typ[byte] (an alias) - in the other cases, the type name
 	// is chosen by the source. Either way, byte and uint8 denote identical types.
-	{_Append, `var s []byte; _ = append(s, "foo"...)`, `func([]byte, ...uint8) []byte`},
-	{_Append, `type T []byte; var s T; _ = append(s, "foo"...)`, `func(p.T, ...uint8) p.T`},
+	{"append", `var s []byte; _ = append(s, "foo"...)`, `func([]byte, ...uint8) []byte`},
+	{"append", `type T []byte; var s T; _ = append(s, "foo"...)`, `func(p.T, ...uint8) p.T`},
 
-	{_Cap, `var s [10]int; _ = cap(s)`, `invalid type`},  // constant
-	{_Cap, `var s [10]int; _ = cap(&s)`, `invalid type`}, // constant
-	{_Cap, `var s []int64; _ = cap(s)`, `func([]int64) int`},
-	{_Cap, `var c chan<-bool; _ = cap(c)`, `func(chan<- bool) int`},
+	{"cap", `var s [10]int; _ = cap(s)`, `invalid type`},  // constant
+	{"cap", `var s [10]int; _ = cap(&s)`, `invalid type`}, // constant
+	{"cap", `var s []int64; _ = cap(s)`, `func([]int64) int`},
+	{"cap", `var c chan<-bool; _ = cap(c)`, `func(chan<- bool) int`},
 
-	{_Len, `_ = len("foo")`, `invalid type`}, // constant
-	{_Len, `var s string; _ = len(s)`, `func(string) int`},
-	{_Len, `var s [10]int; _ = len(s)`, `invalid type`},  // constant
-	{_Len, `var s [10]int; _ = len(&s)`, `invalid type`}, // constant
-	{_Len, `var s []int64; _ = len(s)`, `func([]int64) int`},
-	{_Len, `var c chan<-bool; _ = len(c)`, `func(chan<- bool) int`},
-	{_Len, `var m map[string]float32; _ = len(m)`, `func(map[string]float32) int`},
+	{"len", `_ = len("foo")`, `invalid type`}, // constant
+	{"len", `var s string; _ = len(s)`, `func(string) int`},
+	{"len", `var s [10]int; _ = len(s)`, `invalid type`},  // constant
+	{"len", `var s [10]int; _ = len(&s)`, `invalid type`}, // constant
+	{"len", `var s []int64; _ = len(s)`, `func([]int64) int`},
+	{"len", `var c chan<-bool; _ = len(c)`, `func(chan<- bool) int`},
+	{"len", `var m map[string]float32; _ = len(m)`, `func(map[string]float32) int`},
 
-	{_Close, `var c chan int; close(c)`, `func(chan int)`},
-	{_Close, `var c chan<- chan string; close(c)`, `func(chan<- chan string)`},
+	{"close", `var c chan int; close(c)`, `func(chan int)`},
+	{"close", `var c chan<- chan string; close(c)`, `func(chan<- chan string)`},
 
-	{_Complex, `_ = complex(1, 0)`, `invalid type`}, // constant
-	{_Complex, `var re float32; _ = complex(re, 1.0)`, `func(float32, float32) complex64`},
-	{_Complex, `var im float64; _ = complex(1, im)`, `func(float64, float64) complex128`},
-	{_Complex, `type F32 float32; var re, im F32; _ = complex(re, im)`, `func(p.F32, p.F32) complex64`},
-	{_Complex, `type F64 float64; var re, im F64; _ = complex(re, im)`, `func(p.F64, p.F64) complex128`},
+	{"complex", `_ = complex(1, 0)`, `invalid type`}, // constant
+	{"complex", `var re float32; _ = complex(re, 1.0)`, `func(float32, float32) complex64`},
+	{"complex", `var im float64; _ = complex(1, im)`, `func(float64, float64) complex128`},
+	{"complex", `type F32 float32; var re, im F32; _ = complex(re, im)`, `func(p.F32, p.F32) complex64`},
+	{"complex", `type F64 float64; var re, im F64; _ = complex(re, im)`, `func(p.F64, p.F64) complex128`},
 
-	{_Copy, `var src, dst []byte; copy(dst, src)`, `func([]byte, []byte) int`},
-	{_Copy, `type T [][]int; var src, dst T; _ = copy(dst, src)`, `func([][]int, [][]int) int`},
+	{"copy", `var src, dst []byte; copy(dst, src)`, `func([]byte, []byte) int`},
+	{"copy", `type T [][]int; var src, dst T; _ = copy(dst, src)`, `func([][]int, [][]int) int`},
 
-	{_Delete, `var m map[string]bool; delete(m, "foo")`, `func(map[string]bool, string)`},
-	{_Delete, `type (K string; V int); var m map[K]V; delete(m, "foo")`, `func(map[p.K]p.V, p.K)`},
+	{"delete", `var m map[string]bool; delete(m, "foo")`, `func(map[string]bool, string)`},
+	{"delete", `type (K string; V int); var m map[K]V; delete(m, "foo")`, `func(map[p.K]p.V, p.K)`},
 
-	{_Imag, `_ = imag(1i)`, `invalid type`}, // constant
-	{_Imag, `var c complex64; _ = imag(c)`, `func(complex64) float32`},
-	{_Imag, `var c complex128; _ = imag(c)`, `func(complex128) float64`},
-	{_Imag, `type C64 complex64; var c C64; _ = imag(c)`, `func(p.C64) float32`},
-	{_Imag, `type C128 complex128; var c C128; _ = imag(c)`, `func(p.C128) float64`},
+	{"imag", `_ = imag(1i)`, `invalid type`}, // constant
+	{"imag", `var c complex64; _ = imag(c)`, `func(complex64) float32`},
+	{"imag", `var c complex128; _ = imag(c)`, `func(complex128) float64`},
+	{"imag", `type C64 complex64; var c C64; _ = imag(c)`, `func(p.C64) float32`},
+	{"imag", `type C128 complex128; var c C128; _ = imag(c)`, `func(p.C128) float64`},
 
-	{_Real, `_ = real(1i)`, `invalid type`}, // constant
-	{_Real, `var c complex64; _ = real(c)`, `func(complex64) float32`},
-	{_Real, `var c complex128; _ = real(c)`, `func(complex128) float64`},
-	{_Real, `type C64 complex64; var c C64; _ = real(c)`, `func(p.C64) float32`},
-	{_Real, `type C128 complex128; var c C128; _ = real(c)`, `func(p.C128) float64`},
+	{"real", `_ = real(1i)`, `invalid type`}, // constant
+	{"real", `var c complex64; _ = real(c)`, `func(complex64) float32`},
+	{"real", `var c complex128; _ = real(c)`, `func(complex128) float64`},
+	{"real", `type C64 complex64; var c C64; _ = real(c)`, `func(p.C64) float32`},
+	{"real", `type C128 complex128; var c C128; _ = real(c)`, `func(p.C128) float64`},
 
-	{_Make, `_ = make([]int, 10)`, `func([]int, int) []int`},
-	{_Make, `type T []byte; _ = make(T, 10, 20)`, `func(p.T, int, int) p.T`},
+	{"make", `_ = make([]int, 10)`, `func([]int, int) []int`},
+	{"make", `type T []byte; _ = make(T, 10, 20)`, `func(p.T, int, int) p.T`},
 
-	{_New, `_ = new(int)`, `func(int) *int`},
-	{_New, `type T struct{}; _ = new(T)`, `func(p.T) *p.T`},
+	{"new", `_ = new(int)`, `func(int) *int`},
+	{"new", `type T struct{}; _ = new(T)`, `func(p.T) *p.T`},
 
-	{_Panic, `panic(0)`, `func(interface{})`},
-	{_Panic, `panic("foo")`, `func(interface{})`},
+	{"panic", `panic(0)`, `func(interface{})`},
+	{"panic", `panic("foo")`, `func(interface{})`},
 
-	{_Print, `print()`, `func()`},
-	{_Print, `print(0)`, `func(int)`},
-	{_Print, `print(1, 2.0, "foo", true)`, `func(int, float64, string, bool)`},
+	{"print", `print()`, `func()`},
+	{"print", `print(0)`, `func(int)`},
+	{"print", `print(1, 2.0, "foo", true)`, `func(int, float64, string, bool)`},
 
-	{_Println, `println()`, `func()`},
-	{_Println, `println(0)`, `func(int)`},
-	{_Println, `println(1, 2.0, "foo", true)`, `func(int, float64, string, bool)`},
+	{"println", `println()`, `func()`},
+	{"println", `println(0)`, `func(int)`},
+	{"println", `println(1, 2.0, "foo", true)`, `func(int, float64, string, bool)`},
 
-	{_Recover, `recover()`, `func() interface{}`},
-	{_Recover, `_ = recover()`, `func() interface{}`},
+	{"recover", `recover()`, `func() interface{}`},
+	{"recover", `_ = recover()`, `func() interface{}`},
 
-	{_Alignof, `_ = unsafe.Alignof(0)`, `invalid type`},                 // constant
-	{_Alignof, `var x struct{}; _ = unsafe.Alignof(x)`, `invalid type`}, // constant
+	{"Alignof", `_ = unsafe.Alignof(0)`, `invalid type`},                 // constant
+	{"Alignof", `var x struct{}; _ = unsafe.Alignof(x)`, `invalid type`}, // constant
 
-	{_Offsetof, `var x struct{f bool}; _ = unsafe.Offsetof(x.f)`, `invalid type`},           // constant
-	{_Offsetof, `var x struct{_ int; f bool}; _ = unsafe.Offsetof((&x).f)`, `invalid type`}, // constant
+	{"Offsetof", `var x struct{f bool}; _ = unsafe.Offsetof(x.f)`, `invalid type`},           // constant
+	{"Offsetof", `var x struct{_ int; f bool}; _ = unsafe.Offsetof((&x).f)`, `invalid type`}, // constant
 
-	{_Sizeof, `_ = unsafe.Sizeof(0)`, `invalid type`},                 // constant
-	{_Sizeof, `var x struct{}; _ = unsafe.Sizeof(x)`, `invalid type`}, // constant
+	{"Sizeof", `_ = unsafe.Sizeof(0)`, `invalid type`},                 // constant
+	{"Sizeof", `var x struct{}; _ = unsafe.Sizeof(x)`, `invalid type`}, // constant
 
-	{_Assert, `assert(true)`, `invalid type`},                                    // constant
-	{_Assert, `type B bool; const pred B = 1 < 2; assert(pred)`, `invalid type`}, // constant
+	{"assert", `assert(true)`, `invalid type`},                                    // constant
+	{"assert", `type B bool; const pred B = 1 < 2; assert(pred)`, `invalid type`}, // constant
 
 	// no tests for trace since it produces output as a side-effect
 }
 
 func TestBuiltinSignatures(t *testing.T) {
-	defPredeclaredTestFuncs()
+	DefPredeclaredTestFuncs()
 
-	seen := map[builtinId]bool{_Trace: true} // no test for _Trace; add it manually
+	seen := map[string]bool{"trace": true} // no test for trace built-in; add it manually
 	for _, call := range builtinCalls {
-		testBuiltinSignature(t, call.id, call.src, call.sig)
-		seen[call.id] = true
+		testBuiltinSignature(t, call.name, call.src, call.sig)
+		seen[call.name] = true
 	}
 
 	// make sure we didn't miss one
-	for i := range predeclaredFuncs {
-		if id := builtinId(i); !seen[id] {
-			t.Errorf("missing test for %s", predeclaredFuncs[id].name)
+	for _, name := range Universe.Names() {
+		if _, ok := Universe.Lookup(name).(*Builtin); ok && !seen[name] {
+			t.Errorf("missing test for %s", name)
+		}
+	}
+	for _, name := range Unsafe.Scope().Names() {
+		if _, ok := Unsafe.Scope().Lookup(name).(*Builtin); ok && !seen[name] {
+			t.Errorf("missing test for unsafe.%s", name)
 		}
 	}
 }
 
-func testBuiltinSignature(t *testing.T, id builtinId, src0, want string) {
+func testBuiltinSignature(t *testing.T, name, src0, want string) {
 	src := fmt.Sprintf(`package p; import "unsafe"; type _ unsafe.Pointer /* use unsafe */; func _() { %s }`, src0)
 	f, err := parser.ParseFile(fset, "", src, 0)
 	if err != nil {
@@ -154,7 +160,7 @@ func testBuiltinSignature(t *testing.T, id builtinId, src0, want string) {
 		// the recorded type for the built-in must match the wanted signature
 		typ := types[fun]
 		if typ == nil {
-			t.Errorf("%s: no type recorded for %s", src0, exprString(fun))
+			t.Errorf("%s: no type recorded for %s", src0, ExprString(fun))
 			return
 		}
 		if got := typ.String(); got != want {
@@ -176,8 +182,8 @@ func testBuiltinSignature(t *testing.T, id builtinId, src0, want string) {
 				t.Errorf("%s: %s does not denote a built-in", src0, p)
 				return
 			}
-			if bin.id != id {
-				t.Errorf("%s: got built-in %s; want %s", src0, bin.name, predeclaredFuncs[id].name)
+			if bin.Name() != name {
+				t.Errorf("%s: got built-in %s; want %s", src0, bin.Name(), name)
 				return
 			}
 			return // we're done
diff --git a/go/types/check_test.go b/go/types/check_test.go
index 70e8de26..3c5f6967 100644
--- a/go/types/check_test.go
+++ b/go/types/check_test.go
@@ -20,7 +20,7 @@
 //		_ = x /* ERROR "not declared" */ + 1
 //	}
 
-package types
+package types_test
 
 import (
 	"flag"
@@ -32,6 +32,9 @@ import (
 	"regexp"
 	"strings"
 	"testing"
+
+	_ "code.google.com/p/go.tools/go/gcimporter"
+	. "code.google.com/p/go.tools/go/types"
 )
 
 var (
@@ -254,7 +257,7 @@ func checkFiles(t *testing.T, testfiles []string) {
 
 func TestCheck(t *testing.T) {
 	// Declare builtins for testing.
-	defPredeclaredTestFuncs()
+	DefPredeclaredTestFuncs()
 
 	// If explicit test files are specified, only check those.
 	if files := *testFiles; files != "" {
diff --git a/go/types/errors.go b/go/types/errors.go
index 7c63653d..346effdb 100644
--- a/go/types/errors.go
+++ b/go/types/errors.go
@@ -34,7 +34,7 @@ func (check *checker) sprintf(format string, args ...interface{}) string {
 		case token.Pos:
 			args[i] = check.fset.Position(a).String()
 		case ast.Expr:
-			args[i] = exprString(a)
+			args[i] = ExprString(a)
 		}
 	}
 	return fmt.Sprintf(format, args...)
@@ -82,14 +82,14 @@ func (check *checker) invalidOp(pos token.Pos, format string, args ...interface{
 }
 
 // exprString returns a (simplified) string representation for an expression.
-func exprString(expr ast.Expr) string {
+func ExprString(expr ast.Expr) string {
 	var buf bytes.Buffer
-	writeExpr(&buf, expr)
+	WriteExpr(&buf, expr)
 	return buf.String()
 }
 
 // TODO(gri) Need to merge with typeString since some expressions are types (try: ([]int)(a))
-func writeExpr(buf *bytes.Buffer, expr ast.Expr) {
+func WriteExpr(buf *bytes.Buffer, expr ast.Expr) {
 	switch x := expr.(type) {
 	case *ast.Ident:
 		buf.WriteString(x.Name)
@@ -105,66 +105,66 @@ func writeExpr(buf *bytes.Buffer, expr ast.Expr) {
 
 	case *ast.ParenExpr:
 		buf.WriteByte('(')
-		writeExpr(buf, x.X)
+		WriteExpr(buf, x.X)
 		buf.WriteByte(')')
 
 	case *ast.SelectorExpr:
-		writeExpr(buf, x.X)
+		WriteExpr(buf, x.X)
 		buf.WriteByte('.')
 		buf.WriteString(x.Sel.Name)
 
 	case *ast.IndexExpr:
-		writeExpr(buf, x.X)
+		WriteExpr(buf, x.X)
 		buf.WriteByte('[')
-		writeExpr(buf, x.Index)
+		WriteExpr(buf, x.Index)
 		buf.WriteByte(']')
 
 	case *ast.SliceExpr:
-		writeExpr(buf, x.X)
+		WriteExpr(buf, x.X)
 		buf.WriteByte('[')
 		if x.Low != nil {
-			writeExpr(buf, x.Low)
+			WriteExpr(buf, x.Low)
 		}
 		buf.WriteByte(':')
 		if x.High != nil {
-			writeExpr(buf, x.High)
+			WriteExpr(buf, x.High)
 		}
 		buf.WriteByte(']')
 
 	case *ast.TypeAssertExpr:
-		writeExpr(buf, x.X)
+		WriteExpr(buf, x.X)
 		buf.WriteString(".(")
-		// TODO(gri) expand writeExpr so that types are not handled by default case
-		writeExpr(buf, x.Type)
+		// TODO(gri) expand WriteExpr so that types are not handled by default case
+		WriteExpr(buf, x.Type)
 		buf.WriteByte(')')
 
 	case *ast.CallExpr:
-		writeExpr(buf, x.Fun)
+		WriteExpr(buf, x.Fun)
 		buf.WriteByte('(')
 		for i, arg := range x.Args {
 			if i > 0 {
 				buf.WriteString(", ")
 			}
-			writeExpr(buf, arg)
+			WriteExpr(buf, arg)
 		}
 		buf.WriteByte(')')
 
 	case *ast.StarExpr:
 		buf.WriteByte('*')
-		writeExpr(buf, x.X)
+		WriteExpr(buf, x.X)
 
 	case *ast.UnaryExpr:
 		buf.WriteString(x.Op.String())
-		writeExpr(buf, x.X)
+		WriteExpr(buf, x.X)
 
 	case *ast.BinaryExpr:
 		// The AST preserves source-level parentheses so there is
 		// no need to introduce parentheses here for correctness.
-		writeExpr(buf, x.X)
+		WriteExpr(buf, x.X)
 		buf.WriteByte(' ')
 		buf.WriteString(x.Op.String())
 		buf.WriteByte(' ')
-		writeExpr(buf, x.Y)
+		WriteExpr(buf, x.Y)
 
 	default:
 		// TODO(gri) Consider just calling x.String(). May cause
@@ -228,7 +228,7 @@ func writeType(buf *bytes.Buffer, typ Type) {
 		buf.WriteString("<nil>")
 
 	case *Basic:
-		if t.Kind() == UnsafePointer {
+		if t.kind == UnsafePointer {
 			buf.WriteString("unsafe.")
 		}
 		buf.WriteString(t.name)
@@ -269,9 +269,6 @@ func writeType(buf *bytes.Buffer, typ Type) {
 		buf.WriteString("func")
 		writeSignature(buf, t)
 
-	case *Builtin:
-		fmt.Fprintf(buf, "<type of %s>", t.name)
-
 	case *Interface:
 		// We write the source-level methods and embedded types rather
 		// than the actual method set since resolved method signatures
diff --git a/go/types/eval_test.go b/go/types/eval_test.go
index 41663185..097cc0b5 100644
--- a/go/types/eval_test.go
+++ b/go/types/eval_test.go
@@ -4,7 +4,7 @@
 
 // This file contains tests for Eval.
 
-package types
+package types_test
 
 import (
 	"go/ast"
@@ -12,6 +12,9 @@ import (
 	"go/token"
 	"strings"
 	"testing"
+
+	_ "code.google.com/p/go.tools/go/gcimporter"
+	. "code.google.com/p/go.tools/go/types"
 )
 
 func testEval(t *testing.T, pkg *Package, scope *Scope, str string, typ Type, typStr, valStr string) {
@@ -53,7 +56,7 @@ func testEval(t *testing.T, pkg *Package, scope *Scope, str string, typ Type, ty
 
 func TestEvalBasic(t *testing.T) {
 	for _, typ := range Typ[Bool : String+1] {
-		testEval(t, nil, nil, typ.name, typ, "", "")
+		testEval(t, nil, nil, typ.Name(), typ, "", "")
 	}
 }
 
@@ -106,7 +109,7 @@ func f(a int, s string) float64 {
 		t.Fatal(err)
 	}
 
-	pkgScope := pkg.scope
+	pkgScope := pkg.Scope()
 	if n := pkgScope.NumChildren(); n != 1 {
 		t.Fatalf("got %d file scopes, want 1", n)
 	}
diff --git a/go/types/issues_test.go b/go/types/issues_test.go
index 7d8126b9..3cfa2018 100644
--- a/go/types/issues_test.go
+++ b/go/types/issues_test.go
@@ -4,13 +4,16 @@
 
 // This file implements tests for various issues.
 
-package types
+package types_test
 
 import (
 	"go/ast"
 	"go/parser"
 	"strings"
 	"testing"
+
+	_ "code.google.com/p/go.tools/go/gcimporter"
+	. "code.google.com/p/go.tools/go/types"
 )
 
 func TestIssue5770(t *testing.T) {
@@ -78,28 +81,6 @@ var (
 	}
 }
 
-func TestIssue5815(t *testing.T) {
-	pkg, err := GcImport(make(map[string]*Package), "strings")
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	for _, obj := range pkg.scope.elems {
-		if obj.Pkg() == nil {
-			t.Errorf("no pkg for %s", obj)
-		}
-		if tname, _ := obj.(*TypeName); tname != nil {
-			if named, _ := tname.typ.(*Named); named != nil {
-				for _, m := range named.methods {
-					if m.pkg == nil {
-						t.Errorf("no pkg for %s", m)
-					}
-				}
-			}
-		}
-	}
-}
-
 func TestIssue6413(t *testing.T) {
 	src := `
 package p
diff --git a/go/types/operand.go b/go/types/operand.go
index 57fe32f9..85c67922 100644
--- a/go/types/operand.go
+++ b/go/types/operand.go
@@ -99,7 +99,7 @@ func (x *operand) String() string {
 
 	var expr string
 	if x.expr != nil {
-		expr = exprString(x.expr)
+		expr = ExprString(x.expr)
 	} else {
 		switch x.mode {
 		case builtin:
diff --git a/go/types/package.go b/go/types/package.go
index 06803e13..dc6c78ea 100644
--- a/go/types/package.go
+++ b/go/types/package.go
@@ -4,6 +4,8 @@
 
 package types
 
+import "fmt"
+
 // A Package describes a Go package.
 type Package struct {
 	path     string
@@ -39,3 +41,10 @@ func (pkg *Package) Complete() bool { return pkg.complete }
 // Imports returns the list of packages explicitly imported by
 // pkg; the list is in source order. Package unsafe is excluded.
 func (pkg *Package) Imports() []*Package { return pkg.imports }
+
+// MarkComplete marks a package as complete.
+func (pkg *Package) MarkComplete() { pkg.complete = true }
+
+func (pkg *Package) String() string {
+	return fmt.Sprintf("package %s (%s)", pkg.name, pkg.path)
+}
diff --git a/go/types/resolver.go b/go/types/resolver.go
index 26e69bfa..daddb8b1 100644
--- a/go/types/resolver.go
+++ b/go/types/resolver.go
@@ -146,7 +146,10 @@ func (check *checker) resolveFiles(files []*ast.File) {
 
 	importer := check.conf.Import
 	if importer == nil {
-		importer = GcImport
+		if DefaultImport == nil {
+			panic("no Config.Import and no DefaultImport")
+		}
+		importer = DefaultImport
 	}
 
 	var (
diff --git a/go/types/resolver_test.go b/go/types/resolver_test.go
index 91ead4b7..5c8a97e9 100644
--- a/go/types/resolver_test.go
+++ b/go/types/resolver_test.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package types
+package types_test
 
 import (
 	"fmt"
@@ -10,6 +10,9 @@ import (
 	"go/parser"
 	"go/token"
 	"testing"
+
+	_ "code.google.com/p/go.tools/go/gcimporter"
+	. "code.google.com/p/go.tools/go/types"
 )
 
 var sources = []string{
diff --git a/go/types/self_test.go b/go/types/self_test.go
index befc46bc..08fb1edf 100644
--- a/go/types/self_test.go
+++ b/go/types/self_test.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package types
+package types_test
 
 import (
 	"fmt"
@@ -11,6 +11,9 @@ import (
 	"go/token"
 	"testing"
 	"time"
+
+	_ "code.google.com/p/go.tools/go/gcimporter"
+	. "code.google.com/p/go.tools/go/types"
 )
 
 func TestSelf(t *testing.T) {
diff --git a/go/types/stdlib_test.go b/go/types/stdlib_test.go
index 32f66523..1816df4a 100644
--- a/go/types/stdlib_test.go
+++ b/go/types/stdlib_test.go
@@ -5,7 +5,7 @@
 // This file tests types.Check by using it to
 // typecheck the standard library and tests.
 
-package types
+package types_test
 
 import (
 	"flag"
@@ -22,6 +22,9 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	_ "code.google.com/p/go.tools/go/gcimporter"
+	. "code.google.com/p/go.tools/go/types"
 )
 
 var verbose = flag.Bool("types.v", false, "verbose mode")
diff --git a/go/types/types.go b/go/types/types.go
index 91c4f632..209288c9 100644
--- a/go/types/types.go
+++ b/go/types/types.go
@@ -139,6 +139,15 @@ type Struct struct {
 // only as long as required to hold the tag with the largest index i. Consequently,
 // if no field has a tag, tags may be nil.
 func NewStruct(fields []*Var, tags []string) *Struct {
+	var fset objset
+	for _, f := range fields {
+		if f.name != "_" && fset.insert(f) != nil {
+			panic("multiple fields with the same name")
+		}
+	}
+	if len(tags) > len(fields) {
+		panic("more tags than fields")
+	}
 	return &Struct{fields: fields, tags: tags}
 }
 
@@ -249,9 +258,25 @@ type Interface struct {
 }
 
 // NewInterface returns a new interface for the given methods.
-func NewInterface(methods []*Func) *Interface {
-	// TODO(gri) should provide receiver to all methods
+func NewInterface(methods []*Func, types []*Named) *Interface {
+	typ := new(Interface)
+
+	var mset objset
+	for _, m := range methods {
+		if mset.insert(m) != nil {
+			panic("multiple methods with the same name")
+		}
+		// set receiver
+		// TODO(gri) Ideally, we should use a named type here instead of
+		// typ, for less verbose printing of interface method signatures.
+		m.typ.(*Signature).recv = NewVar(m.pos, m.pkg, "", typ)
+	}
 	sort.Sort(byUniqueMethodName(methods))
+
+	if types != nil {
+		panic("unimplemented")
+	}
+
 	return &Interface{methods: methods, allMethods: methods}
 }
 
@@ -304,13 +329,12 @@ type Named struct {
 }
 
 // NewNamed returns a new named type for the given type name, underlying type, and associated methods.
-// The underlying type must exist and not be a *Named, and the methods scope entries must be *Func
-// objects if the scope is not empty.
+// The underlying type must not be a *Named.
 func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named {
 	if _, ok := underlying.(*Named); ok {
 		panic("types.NewNamed: underlying type must not be *Named")
 	}
-	typ := &Named{obj: obj, underlying: underlying, complete: true, methods: methods}
+	typ := &Named{obj: obj, underlying: underlying, complete: underlying != nil, methods: methods}
 	if obj.typ == nil {
 		obj.typ = typ
 	}
@@ -326,6 +350,27 @@ func (t *Named) NumMethods() int { return len(t.methods) }
 // Method returns the i'th method of named type t for 0 <= i < t.NumMethods().
 func (t *Named) Method(i int) *Func { return t.methods[i] }
 
+// SetUnderlying sets the underlying type and marks t as complete.
+// TODO(gri) determine if there's a better solution rather than providing this function
+func (t *Named) SetUnderlying(underlying Type) {
+	if underlying == nil {
+		panic("types.Named.SetUnderlying: underlying type must not be nil")
+	}
+	if _, ok := underlying.(*Named); ok {
+		panic("types.Named.SetUnderlying: underlying type must not be *Named")
+	}
+	t.underlying = underlying
+	t.complete = true
+}
+
+// AddMethod adds method m unless it is already in the method list.
+// TODO(gri) find a better solution instead of providing this function
+func (t *Named) AddMethod(m *Func) {
+	if i, _ := lookupMethod(t.methods, m.pkg, m.name); i < 0 {
+		t.methods = append(t.methods, m)
+	}
+}
+
 // Implementations for Type methods.
 
 func (t *Basic) Underlying() Type     { return t }
@@ -335,7 +380,6 @@ func (t *Struct) Underlying() Type    { return t }
 func (t *Pointer) Underlying() Type   { return t }
 func (t *Tuple) Underlying() Type     { return t }
 func (t *Signature) Underlying() Type { return t }
-func (t *Builtin) Underlying() Type   { return t }
 func (t *Interface) Underlying() Type { return t }
 func (t *Map) Underlying() Type       { return t }
 func (t *Chan) Underlying() Type      { return t }
@@ -355,7 +399,6 @@ func (t *Pointer) MethodSet() *MethodSet {
 }
 func (t *Tuple) MethodSet() *MethodSet     { return &emptyMethodSet }
 func (t *Signature) MethodSet() *MethodSet { return &emptyMethodSet }
-func (t *Builtin) MethodSet() *MethodSet   { return &emptyMethodSet }
 func (t *Interface) MethodSet() *MethodSet { return t.mset.of(t) }
 func (t *Map) MethodSet() *MethodSet       { return &emptyMethodSet }
 func (t *Chan) MethodSet() *MethodSet      { return &emptyMethodSet }
@@ -368,7 +411,6 @@ func (t *Struct) String() string    { return typeString(t) }
 func (t *Pointer) String() string   { return typeString(t) }
 func (t *Tuple) String() string     { return typeString(t) }
 func (t *Signature) String() string { return typeString(t) }
-func (t *Builtin) String() string   { return typeString(t) }
 func (t *Interface) String() string { return typeString(t) }
 func (t *Map) String() string       { return typeString(t) }
 func (t *Chan) String() string      { return typeString(t) }
diff --git a/go/types/types_test.go b/go/types/types_test.go
index af4fdb7d..31d1a744 100644
--- a/go/types/types_test.go
+++ b/go/types/types_test.go
@@ -5,12 +5,15 @@
 // This file contains tests verifying the types associated with an AST after
 // type checking.
 
-package types
+package types_test
 
 import (
 	"go/ast"
 	"go/parser"
 	"testing"
+
+	_ "code.google.com/p/go.tools/go/gcimporter"
+	. "code.google.com/p/go.tools/go/types"
 )
 
 const filename = "<src>"
@@ -122,8 +125,8 @@ func TestTypes(t *testing.T) {
 			t.Errorf("%s: %s", src, err)
 			continue
 		}
-		typ := pkg.scope.Lookup("T").Type().Underlying()
-		str := typeString(typ)
+		typ := pkg.Scope().Lookup("T").Type().Underlying()
+		str := typ.String()
 		if str != test.str {
 			t.Errorf("%s: got %s, want %s", test.src, str, test.str)
 		}
@@ -171,7 +174,7 @@ func TestExprs(t *testing.T) {
 			t.Errorf("%s: %s", src, err)
 			continue
 		}
-		str := exprString(file.Decls[0].(*ast.GenDecl).Specs[0].(*ast.ValueSpec).Values[0])
+		str := ExprString(file.Decls[0].(*ast.GenDecl).Specs[0].(*ast.ValueSpec).Values[0])
 		if str != test.str {
 			t.Errorf("%s: got %s, want %s", test.src, str, test.str)
 		}
diff --git a/go/types/universe.go b/go/types/universe.go
index 63a6be11..2e57b880 100644
--- a/go/types/universe.go
+++ b/go/types/universe.go
@@ -67,7 +67,7 @@ func defPredeclaredTypes() {
 	res := NewVar(token.NoPos, nil, "", Typ[String])
 	sig := &Signature{results: NewTuple(res)}
 	err := NewFunc(token.NoPos, nil, "Error", sig)
-	typ := &Named{underlying: NewInterface([]*Func{err}), complete: true}
+	typ := &Named{underlying: NewInterface([]*Func{err}, nil), complete: true}
 	sig.recv = NewVar(token.NoPos, nil, "", typ)
 	def(NewTypeName(token.NoPos, nil, "error", typ))
 }
@@ -163,7 +163,10 @@ func defPredeclaredFuncs() {
 	}
 }
 
-func defPredeclaredTestFuncs() {
+// DefPredeclaredTestFuncs defines the assert and trace built-ins.
+// These built-ins are intended for debugging and testing of this
+// package only.
+func DefPredeclaredTestFuncs() {
 	if Universe.Lookup("assert") != nil {
 		return // already defined
 	}
diff --git a/importer/importer.go b/importer/importer.go
index 70be1da7..c0ec0ecc 100644
--- a/importer/importer.go
+++ b/importer/importer.go
@@ -53,17 +53,15 @@ import (
 	"sync"
 
 	"code.google.com/p/go.tools/go/exact"
+	"code.google.com/p/go.tools/go/gcimporter"
 	"code.google.com/p/go.tools/go/types"
 )
 
-// Alias for type of types.Config.Import function.
-type importfn func(map[string]*types.Package, string) (*types.Package, error)
-
 // An Importer's exported methods are not thread-safe.
 type Importer struct {
 	Fset          *token.FileSet         // position info for all files seen
 	config        Config                 // the client configuration, modified by us
-	importfn      importfn               // client's type import function
+	importfn      types.Importer         // client's type import function
 	augment       map[string]bool        // packages to be augmented by TestFiles when imported
 	allPackagesMu sync.Mutex             // guards 'allPackages' during internal concurrency
 	allPackages   []*PackageInfo         // all packages, including non-importable ones
@@ -103,7 +101,7 @@ type Config struct {
 func New(config *Config) *Importer {
 	importfn := config.TypeChecker.Import
 	if importfn == nil {
-		importfn = types.GcImport
+		importfn = gcimporter.Import
 	}
 
 	imp := &Importer{
diff --git a/oracle/describe.go b/oracle/describe.go
index 3426dcea..a6cb702f 100644
--- a/oracle/describe.go
+++ b/oracle/describe.go
@@ -196,7 +196,7 @@ func findInterestingNode(pkginfo *importer.PackageInfo, path []ast.Node) ([]ast.
 			continue
 
 		case *ast.Ident:
-			switch obj := pkginfo.ObjectOf(n).(type) {
+			switch pkginfo.ObjectOf(n).(type) {
 			case *types.PkgName:
 				return path, actionPackage
 
@@ -227,15 +227,12 @@ func findInterestingNode(pkginfo *importer.PackageInfo, path []ast.Node) ([]ast.
 						return path[3:], actionType
 					}
 				}
-
-				// For reference to built-in function, return enclosing call.
-				if _, ok := obj.Type().(*types.Builtin); ok {
-					// Ascend to enclosing function call.
-					path = path[1:]
-					continue
-				}
-
 				return path, actionExpr
+
+			case *types.Builtin:
+				// For reference to built-in function, return enclosing call.
+				path = path[1:] // ascend to enclosing function call
+				continue
 			}
 
 			// No object.
diff --git a/pointer/gen.go b/pointer/gen.go
index 89143c93..297ad633 100644
--- a/pointer/gen.go
+++ b/pointer/gen.go
@@ -20,7 +20,7 @@ import (
 )
 
 var (
-	tEface     = types.NewInterface(nil)
+	tEface     = types.NewInterface(nil, nil)
 	tInvalid   = types.Typ[types.Invalid]
 	tUnsafePtr = types.Typ[types.UnsafePointer]
 )
diff --git a/pointer/util.go b/pointer/util.go
index aa30f585..10350169 100644
--- a/pointer/util.go
+++ b/pointer/util.go
@@ -161,9 +161,6 @@ func (a *analysis) flatten(t types.Type) []*fieldInfo {
 				}
 			}
 
-		case *types.Builtin:
-			panic("flatten(*types.Builtin)") // not the type of any value
-
 		default:
 			panic(t)
 		}