diff --git a/ssa/expr.go b/ssa/expr.go
index 5a25085b..9b69c4af 100644
--- a/ssa/expr.go
+++ b/ssa/expr.go
@@ -93,6 +93,40 @@ func phisExpr(t Type, phis []llvm.Value) Expr {
 
 // -----------------------------------------------------------------------------
 
+func (p Program) Zero(t Type) Expr {
+	var ret llvm.Value
+	switch u := t.raw.Type.Underlying().(type) {
+	case *types.Basic:
+		kind := u.Kind()
+		switch {
+		case kind >= types.Bool && kind <= types.Uintptr:
+			ret = llvm.ConstInt(p.rawType(u).ll, 0, false)
+		case kind == types.String:
+			ret = p.Zero(p.rtType("String")).impl
+		case kind == types.UnsafePointer:
+			ret = llvm.ConstPointerNull(p.tyVoidPtr())
+		case kind <= types.Float64:
+			ret = llvm.ConstFloat(p.Float64().ll, 0)
+		case kind == types.Float32:
+			ret = llvm.ConstFloat(p.Float32().ll, 0)
+		default:
+			panic("todo")
+		}
+	case *types.Pointer:
+		return Expr{llvm.ConstNull(t.ll), t}
+	case *types.Struct:
+		n := u.NumFields()
+		flds := make([]llvm.Value, n)
+		for i := 0; i < n; i++ {
+			flds[i] = p.Zero(p.rawType(u.Field(i).Type())).impl
+		}
+		ret = llvm.ConstStruct(flds, false)
+	default:
+		log.Panicln("todo:", u)
+	}
+	return Expr{ret, t}
+}
+
 // Null returns a null constant expression.
 func (p Program) Null(t Type) Expr {
 	return Expr{llvm.ConstNull(t.ll), t}
@@ -125,12 +159,6 @@ func (p Program) FloatVal(v float64, t Type) Expr {
 	return Expr{ret, t}
 }
 
-func (p Program) ByteVal(v byte) Expr {
-	t := p.Byte()
-	ret := llvm.ConstInt(t.ll, uint64(v), false)
-	return Expr{ret, t}
-}
-
 // Val returns a constant expression.
 func (p Program) Val(v interface{}) Expr {
 	switch v := v.(type) {
@@ -941,21 +969,6 @@ func (b Builder) Call(fn Expr, args ...Expr) (ret Expr) {
 	return
 }
 
-// The Extract instruction yields component Index of Tuple.
-//
-// This is used to access the results of instructions with multiple
-// return values, such as Call, TypeAssert, Next, UnOp(ARROW) and
-// IndexExpr(Map).
-//
-// Example printed form:
-//
-//	t1 = extract t0 #1
-func (b Builder) Extract(x Expr, index int) (ret Expr) {
-	ret.Type = b.Prog.toType(x.Type.raw.Type.(*types.Tuple).At(index).Type())
-	ret.impl = llvm.CreateExtractValue(b.impl, x.impl, index)
-	return
-}
-
 // A Builtin represents a specific use of a built-in function, e.g. len.
 //
 // Builtins are immutable values.  Builtins do not have addresses.
@@ -1009,7 +1022,7 @@ func (b Builder) BuiltinCall(fn string, args ...Expr) (ret Expr) {
 		ret.Type = prog.Void()
 		for i, arg := range args {
 			if ln && i > 0 {
-				b.InlineCall(b.Pkg.rtFunc("PrintByte"), prog.ByteVal(' '))
+				b.InlineCall(b.Pkg.rtFunc("PrintByte"), prog.IntVal(' ', prog.Byte()))
 			}
 			var fn string
 			typ := arg.Type
@@ -1049,7 +1062,7 @@ func (b Builder) BuiltinCall(fn string, args ...Expr) (ret Expr) {
 			b.InlineCall(b.Pkg.rtFunc(fn), arg)
 		}
 		if ln {
-			b.InlineCall(b.Pkg.rtFunc("PrintByte"), prog.ByteVal('\n'))
+			b.InlineCall(b.Pkg.rtFunc("PrintByte"), prog.IntVal('\n', prog.Byte()))
 		}
 		return
 	case "copy":
diff --git a/ssa/interface.go b/ssa/interface.go
index e497cae9..5aebb33e 100644
--- a/ssa/interface.go
+++ b/ssa/interface.go
@@ -161,11 +161,13 @@ func (b Builder) makeIntfAlloc(tinter Type, rawIntf *types.Interface, typ Type,
 
 func (b Builder) makeIntfByPtr(tinter Type, rawIntf *types.Interface, typ Type, vptr Expr) (ret Expr) {
 	if rawIntf.Empty() {
-		return Expr{b.unsafeEface(b.abiType(typ.raw.Type).impl, vptr.impl), tinter}
+		tabi := b.abiType(typ.raw.Type)
+		return Expr{b.unsafeEface(tabi.impl, vptr.impl), tinter}
 	}
 	panic("todo")
 }
 
+// TODO(xsw): remove MakeAnyIntptr, MakeAnyString
 func (b Builder) makeIntfByIntptr(tinter Type, rawIntf *types.Interface, typ Type, x llvm.Value) (ret Expr) {
 	if rawIntf.Empty() {
 		tptr := b.Prog.Uintptr()
@@ -176,45 +178,7 @@ func (b Builder) makeIntfByIntptr(tinter Type, rawIntf *types.Interface, typ Typ
 	panic("todo")
 }
 
-// The TypeAssert instruction tests whether interface value X has type
-// AssertedType.
-//
-// If !CommaOk, on success it returns v, the result of the conversion
-// (defined below); on failure it panics.
-//
-// If CommaOk: on success it returns a pair (v, true) where v is the
-// result of the conversion; on failure it returns (z, false) where z
-// is AssertedType's zero value.  The components of the pair must be
-// accessed using the Extract instruction.
-//
-// If Underlying: tests whether interface value X has the underlying
-// type AssertedType.
-//
-// If AssertedType is a concrete type, TypeAssert checks whether the
-// dynamic type in interface X is equal to it, and if so, the result
-// of the conversion is a copy of the value in the interface.
-//
-// If AssertedType is an interface, TypeAssert checks whether the
-// dynamic type of the interface is assignable to it, and if so, the
-// result of the conversion is a copy of the interface value X.
-// If AssertedType is a superinterface of X.Type(), the operation will
-// fail iff the operand is nil.  (Contrast with ChangeInterface, which
-// performs no nil-check.)
-//
-// Type() reflects the actual type of the result, possibly a
-// 2-types.Tuple; AssertedType is the asserted type.
-//
-// Depending on the TypeAssert's purpose, Pos may return:
-//   - the ast.CallExpr.Lparen of an explicit T(e) conversion;
-//   - the ast.TypeAssertExpr.Lparen of an explicit e.(T) operation;
-//   - the ast.CaseClause.Case of a case of a type-switch statement;
-//   - the Ident(m).NamePos of an interface method value i.m
-//     (for which TypeAssert may be used to effect the nil check).
-//
-// Example printed form:
-//
-//	t1 = typeassert t0.(int)
-//	t3 = typeassert,ok t2.(T)
+/*
 func (b Builder) TypeAssert(x Expr, assertedTyp Type, commaOk bool) (ret Expr) {
 	if debugInstr {
 		log.Printf("TypeAssert %v, %v, %v\n", x.impl, assertedTyp.raw.Type, commaOk)
@@ -277,10 +241,89 @@ func (b Builder) TypeAssert(x Expr, assertedTyp Type, commaOk bool) (ret Expr) {
 			fnName = "CheckI2String"
 		}
 		return b.InlineCall(pkg.rtFunc(fnName), x)
-	case vkStruct:
 	}
 	panic("todo")
 }
+*/
+
+// The TypeAssert instruction tests whether interface value X has type
+// AssertedType.
+//
+// If !CommaOk, on success it returns v, the result of the conversion
+// (defined below); on failure it panics.
+//
+// If CommaOk: on success it returns a pair (v, true) where v is the
+// result of the conversion; on failure it returns (z, false) where z
+// is AssertedType's zero value.  The components of the pair must be
+// accessed using the Extract instruction.
+//
+// If Underlying: tests whether interface value X has the underlying
+// type AssertedType.
+//
+// If AssertedType is a concrete type, TypeAssert checks whether the
+// dynamic type in interface X is equal to it, and if so, the result
+// of the conversion is a copy of the value in the interface.
+//
+// If AssertedType is an interface, TypeAssert checks whether the
+// dynamic type of the interface is assignable to it, and if so, the
+// result of the conversion is a copy of the interface value X.
+// If AssertedType is a superinterface of X.Type(), the operation will
+// fail iff the operand is nil.  (Contrast with ChangeInterface, which
+// performs no nil-check.)
+//
+// Type() reflects the actual type of the result, possibly a
+// 2-types.Tuple; AssertedType is the asserted type.
+//
+// Depending on the TypeAssert's purpose, Pos may return:
+//   - the ast.CallExpr.Lparen of an explicit T(e) conversion;
+//   - the ast.TypeAssertExpr.Lparen of an explicit e.(T) operation;
+//   - the ast.CaseClause.Case of a case of a type-switch statement;
+//   - the Ident(m).NamePos of an interface method value i.m
+//     (for which TypeAssert may be used to effect the nil check).
+//
+// Example printed form:
+//
+//	t1 = typeassert t0.(int)
+//	t3 = typeassert,ok t2.(T)
+func (b Builder) TypeAssert(x Expr, assertedTyp Type, commaOk bool) Expr {
+	if debugInstr {
+		log.Printf("TypeAssert %v, %v, %v\n", x.impl, assertedTyp.raw.Type, commaOk)
+	}
+	tx := b.faceAbiType(x)
+	tabi := b.abiType(assertedTyp.raw.Type)
+	eq := b.BinOp(token.EQL, tx, tabi)
+	if commaOk {
+		/*
+			prog := b.Prog
+			t := prog.Tuple(assertedTyp, prog.Bool())
+			val := b.valFromData(assertedTyp, b.InterfaceData(x))
+			zero := prog.Zero(assertedTyp)
+			valTrue := aggregateValue(b.impl, t.ll, val.impl, prog.BoolVal(true).impl)
+			valFalse := aggregateValue(b.impl, t.ll, zero.impl, prog.BoolVal(false).impl)
+			return Expr{llvm.CreateSelect(b.impl, eq.impl, valTrue, valFalse), t}
+		*/
+		panic("todo")
+	}
+	blks := b.Func.MakeBlocks(2)
+	b.If(eq, blks[0], blks[1])
+	b.SetBlock(blks[1])
+	b.Panic(b.Str("type assertion failed"))
+	b.SetBlock(blks[0])
+	return b.valFromData(assertedTyp, b.InterfaceData(x))
+}
+
+func (b Builder) valFromData(t Type, data Expr) Expr {
+	switch u := t.raw.Type.Underlying().(type) {
+	case *types.Basic:
+		kind := u.Kind()
+		switch {
+		case kind >= types.Bool && kind <= types.Uintptr:
+			panic("todo")
+		}
+	}
+	_ = data
+	panic("todo")
+}
 
 // -----------------------------------------------------------------------------
 
@@ -293,4 +336,12 @@ func (b Builder) InterfaceData(x Expr) Expr {
 	return Expr{ptr, b.Prog.VoidPtr()}
 }
 
+func (b Builder) faceAbiType(x Expr) Expr {
+	if x.kind == vkIface {
+		panic("todo")
+	}
+	typ := llvm.CreateExtractValue(b.impl, x.impl, 0)
+	return Expr{typ, b.Prog.AbiTypePtr()}
+}
+
 // -----------------------------------------------------------------------------
diff --git a/ssa/package.go b/ssa/package.go
index 879e38ee..f7a967e9 100644
--- a/ssa/package.go
+++ b/ssa/package.go
@@ -137,6 +137,7 @@ type aProgram struct {
 	intTy     Type
 	uintTy    Type
 	f64Ty     Type
+	f32Ty     Type
 	byteTy    Type
 	i32Ty     Type
 	u32Ty     Type
@@ -293,6 +294,16 @@ func (p Program) NewPackage(name, pkgPath string) Package {
 	return ret
 }
 
+// Tuple returns a tuple type.
+func (p Program) Tuple(typs ...Type) Type {
+	n := len(typs)
+	els := make([]*types.Var, n)
+	for i, t := range typs {
+		els[i] = types.NewParam(token.NoPos, nil, "", t.raw.Type)
+	}
+	return p.rawType(types.NewTuple(els...))
+}
+
 // Eface returns the empty interface type.
 func (p Program) Eface() Type {
 	if p.efaceTy == nil {
@@ -418,6 +429,14 @@ func (p Program) Float64() Type {
 	return p.f64Ty
 }
 
+// Float32 returns float32 type.
+func (p Program) Float32() Type {
+	if p.f32Ty == nil {
+		p.f32Ty = p.rawType(types.Typ[types.Float32])
+	}
+	return p.f32Ty
+}
+
 // Byte returns byte type.
 func (p Program) Byte() Type {
 	if p.byteTy == nil {
diff --git a/ssa/stmt_builder.go b/ssa/stmt_builder.go
index 2bbaf771..4ef42c9a 100644
--- a/ssa/stmt_builder.go
+++ b/ssa/stmt_builder.go
@@ -160,6 +160,22 @@ func (b Builder) Return(results ...Expr) {
 	}
 }
 
+// The Extract instruction yields component Index of Tuple.
+//
+// This is used to access the results of instructions with multiple
+// return values, such as Call, TypeAssert, Next, UnOp(ARROW) and
+// IndexExpr(Map).
+//
+// Example printed form:
+//
+//	t1 = extract t0 #1
+func (b Builder) Extract(x Expr, i int) (ret Expr) {
+	if debugInstr {
+		log.Printf("Extract %v, %d\n", x.impl, i)
+	}
+	return b.getField(x, i)
+}
+
 // Jump emits a jump instruction.
 func (b Builder) Jump(jmpb BasicBlock) {
 	if b.Func != jmpb.fn {
diff --git a/ssa/type.go b/ssa/type.go
index 391e95da..64314d6c 100644
--- a/ssa/type.go
+++ b/ssa/type.go
@@ -141,9 +141,14 @@ func (p Program) Index(typ Type) Type {
 }
 
 func (p Program) Field(typ Type, i int) Type {
-	tunder := typ.raw.Type.Underlying()
-	tfld := tunder.(*types.Struct).Field(i).Type()
-	return p.rawType(tfld)
+	var fld *types.Var
+	switch t := typ.raw.Type.(type) {
+	case *types.Tuple:
+		fld = t.At(i)
+	default:
+		fld = t.Underlying().(*types.Struct).Field(i)
+	}
+	return p.rawType(fld.Type())
 }
 
 func (p Program) rawType(raw types.Type) Type {
@@ -218,9 +223,11 @@ func (p Program) tyInt64() llvm.Type {
 	return p.int64Type
 }
 
+/*
 func (p Program) toTuple(typ *types.Tuple) Type {
 	return &aType{p.toLLVMTuple(typ), rawType{typ}, vkTuple}
 }
+*/
 
 func (p Program) toType(raw types.Type) Type {
 	typ := rawType{raw}
@@ -385,7 +392,7 @@ func (p Program) toNamed(raw *types.Named) Type {
 	switch t := raw.Underlying().(type) {
 	case *types.Struct:
 		name := NameOf(raw)
-		return &aType{p.toLLVMNamedStruct(name, t), rawType{raw}, vkInvalid}
+		return &aType{p.toLLVMNamedStruct(name, t), rawType{raw}, vkStruct}
 	default:
 		return p.rawType(t)
 	}