diff --git a/src/examples/hello/hello.go b/src/examples/hello/hello.go
index ea6d14ac..a47ff510 100644
--- a/src/examples/hello/hello.go
+++ b/src/examples/hello/hello.go
@@ -22,12 +22,25 @@ func main() {
 
 	thing := Thing{"foo"}
 	println("thing:", thing.String())
+	printItf(5)
+	printItf(byte('x'))
 }
 
 func strlen(s string) int {
 	return len(s)
 }
 
+func printItf(val interface{}) {
+	switch val := val.(type) {
+	case int:
+		println("is int:", val)
+	case byte:
+		println("is byte:", val)
+	default:
+		println("is ?")
+	}
+}
+
 func calculateAnswer() int {
 	seven := 7
 	return SIX * seven
diff --git a/src/runtime/runtime.c b/src/runtime/runtime.c
index 51cda99c..93ff2024 100644
--- a/src/runtime/runtime.c
+++ b/src/runtime/runtime.c
@@ -26,6 +26,10 @@ void __go_printint(intgo_t n) {
 	putchar((n % 10) + '0');
 }
 
+void __go_printbyte(uint8_t c) {
+	putchar(c);
+}
+
 void __go_printspace() {
 	putchar(' ');
 }
diff --git a/tgo.go b/tgo.go
index ab14d9e6..faa6215d 100644
--- a/tgo.go
+++ b/tgo.go
@@ -37,10 +37,15 @@ type Compiler struct {
 	intType         llvm.Type
 	stringLenType   llvm.Type
 	stringType      llvm.Type
+	interfaceType   llvm.Type
+	typeassertType  llvm.Type
 	printstringFunc llvm.Value
 	printintFunc    llvm.Value
+	printbyteFunc   llvm.Value
 	printspaceFunc  llvm.Value
 	printnlFunc     llvm.Value
+	itfTypeNumbers  map[types.Type]uint64
+	itfTypes        []types.Type
 }
 
 type Frame struct {
@@ -59,7 +64,8 @@ type Phi struct {
 
 func NewCompiler(pkgName, triple string) (*Compiler, error) {
 	c := &Compiler{
-		triple: triple,
+		triple:         triple,
+		itfTypeNumbers: make(map[types.Type]uint64),
 	}
 
 	target, err := llvm.GetTargetFromTriple(triple)
@@ -79,10 +85,18 @@ func NewCompiler(pkgName, triple string) (*Compiler, error) {
 	// Go string: tuple of (len, ptr)
 	c.stringType = llvm.StructType([]llvm.Type{c.stringLenType, llvm.PointerType(llvm.Int8Type(), 0)}, false)
 
+	// Go interface: tuple of (type, ptr)
+	c.interfaceType = llvm.StructType([]llvm.Type{llvm.Int32Type(), llvm.PointerType(llvm.Int8Type(), 0)}, false)
+
+	// Go typeassert result: tuple of (ptr, bool)
+	c.typeassertType = llvm.StructType([]llvm.Type{llvm.PointerType(llvm.Int8Type(), 0), llvm.Int1Type()}, false)
+
 	printstringType := llvm.FunctionType(llvm.VoidType(), []llvm.Type{c.stringType}, false)
 	c.printstringFunc = llvm.AddFunction(c.mod, "__go_printstring", printstringType)
 	printintType := llvm.FunctionType(llvm.VoidType(), []llvm.Type{c.intType}, false)
 	c.printintFunc = llvm.AddFunction(c.mod, "__go_printint", printintType)
+	printbyteType := llvm.FunctionType(llvm.VoidType(), []llvm.Type{llvm.Int8Type()}, false)
+	c.printbyteFunc = llvm.AddFunction(c.mod, "__go_printbyte", printbyteType)
 	printspaceType := llvm.FunctionType(llvm.VoidType(), nil, false)
 	c.printspaceFunc = llvm.AddFunction(c.mod, "__go_printspace", printspaceType)
 	printnlType := llvm.FunctionType(llvm.VoidType(), nil, false)
@@ -154,16 +168,8 @@ func (c *Compiler) Parse(pkgName string) error {
 				}
 				frames[member] = frame
 			case *ssa.NamedConst:
-				val, err := c.parseConst(member.Value)
-				if err != nil {
-					return err
-				}
-				global := llvm.AddGlobal(c.mod, val.Type(), pkgPrefix + "." +  member.Name())
-				global.SetInitializer(val)
-				global.SetGlobalConstant(true)
-				if ast.IsExported(member.Name()) {
-					global.SetLinkage(llvm.PrivateLinkage)
-				}
+				// Ignore package-level untyped constants. The SSA form doesn't
+				// need them.
 			case *ssa.Global:
 				typ, err := c.getLLVMType(member.Type())
 				if err != nil {
@@ -225,6 +231,8 @@ func (c *Compiler) getLLVMType(goType types.Type) (llvm.Type, error) {
 		switch typ.Kind() {
 		case types.Bool:
 			return llvm.Int1Type(), nil
+		case types.Uint8:
+			return llvm.Int8Type(), nil
 		case types.Int:
 			return c.intType, nil
 		case types.Int32:
@@ -236,6 +244,8 @@ func (c *Compiler) getLLVMType(goType types.Type) (llvm.Type, error) {
 		default:
 			return llvm.Type{}, errors.New("todo: unknown basic type: " + fmt.Sprintf("%#v", typ))
 		}
+	case *types.Interface:
+		return c.interfaceType, nil
 	case *types.Named:
 		return c.getLLVMType(typ.Underlying())
 	case *types.Pointer:
@@ -259,6 +269,15 @@ func (c *Compiler) getLLVMType(goType types.Type) (llvm.Type, error) {
 	}
 }
 
+func (c *Compiler) getInterfaceType(typ types.Type) llvm.Value {
+	if _, ok := c.itfTypeNumbers[typ]; !ok {
+		num := uint64(len(c.itfTypes))
+		c.itfTypes = append(c.itfTypes, typ)
+		c.itfTypeNumbers[typ] = num
+	}
+	return llvm.ConstInt(llvm.Int32Type(), c.itfTypeNumbers[typ], false)
+}
+
 func (c *Compiler) getFunctionName(pkgPrefix string, fn *ssa.Function) string {
 	if fn.Signature.Recv() != nil {
 		// Method on a defined type.
@@ -316,6 +335,12 @@ func (c *Compiler) parseFunc(frame *Frame, f *ssa.Function) error {
 		frame.blocks[block] = llvmBlock
 	}
 
+	// Load function parameters
+	for _, param := range f.Params {
+		llvmParam := llvmFn.Param(frame.params[param])
+		frame.locals[param] = llvmParam
+	}
+
 	// Fill those blocks with instructions.
 	for _, block := range f.DomPreorder() {
 		c.builder.SetInsertPointAtEnd(frame.blocks[block])
@@ -412,6 +437,8 @@ func (c *Compiler) parseBuiltin(frame *Frame, instr *ssa.CallCommon, call *ssa.B
 			switch typ := arg.Type().(type) {
 			case *types.Basic:
 				switch typ.Kind() {
+				case types.Uint8:
+					c.builder.CreateCall(c.printbyteFunc, []llvm.Value{value}, "")
 				case types.Int, types.Int32: // TODO: assumes a 32-bit int type
 					c.builder.CreateCall(c.printintFunc, []llvm.Value{value}, "")
 				case types.String:
@@ -506,12 +533,19 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		} else {
 			return c.builder.CreateAlloca(typ, expr.Comment), nil
 		}
-	case *ssa.Const:
-		return c.parseConst(expr)
 	case *ssa.BinOp:
 		return c.parseBinOp(frame, expr)
 	case *ssa.Call:
 		return c.parseCall(frame, expr)
+	case *ssa.Const:
+		return c.parseConst(expr)
+	case *ssa.Extract:
+		value, err := c.parseExpr(frame, expr.Tuple)
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		result := c.builder.CreateExtractValue(value, expr.Index, "")
+		return result, nil
 	case *ssa.FieldAddr:
 		val, err := c.parseExpr(frame, expr.X)
 		if err != nil {
@@ -524,9 +558,16 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		return c.builder.CreateGEP(val, indices, ""), nil
 	case *ssa.Global:
 		return c.mod.NamedGlobal(expr.Name()), nil
-	case *ssa.Parameter:
-		llvmFn := c.mod.NamedFunction(frame.name)
-		return llvmFn.Param(frame.params[expr]), nil
+	case *ssa.MakeInterface:
+		val, err := c.parseExpr(frame, expr.X)
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		bitcast := c.builder.CreateIntToPtr(val, llvm.PointerType(llvm.Int8Type(), 0), "")
+		itfType := c.getInterfaceType(expr.X.Type())
+		itf := c.ctx.ConstStruct([]llvm.Value{itfType, llvm.Undef(llvm.PointerType(llvm.Int8Type(), 0))}, false)
+		itf = c.builder.CreateInsertValue(itf, bitcast, 1, "")
+		return itf, nil
 	case *ssa.Phi:
 		t, err := c.getLLVMType(expr.Type())
 		if err != nil {
@@ -535,6 +576,27 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		phi := c.builder.CreatePHI(t, "")
 		frame.phis = append(frame.phis, Phi{expr, phi})
 		return phi, nil
+	case *ssa.TypeAssert:
+		if !expr.CommaOk {
+			return llvm.Value{}, errors.New("todo: type assert without comma-ok")
+		}
+		itf, err := c.parseExpr(frame, expr.X)
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		assertedType, err := c.getLLVMType(expr.AssertedType)
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		assertedTypeNum := c.getInterfaceType(expr.AssertedType)
+		actualTypeNum := c.builder.CreateExtractValue(itf, 0, "interface.type")
+		valuePtr := c.builder.CreateExtractValue(itf, 1, "interface.value")
+		value := c.builder.CreatePtrToInt(valuePtr, assertedType, "")
+		commaOk := c.builder.CreateICmp(llvm.IntEQ, assertedTypeNum, actualTypeNum, "")
+		tuple := llvm.ConstStruct([]llvm.Value{llvm.Undef(assertedType), llvm.Undef(llvm.Int1Type())}, false) // create empty tuple
+		tuple = c.builder.CreateInsertValue(tuple, value, 0, "") // insert value
+		tuple = c.builder.CreateInsertValue(tuple, commaOk, 1, "") // insert 'comma ok' boolean
+		return tuple, nil
 	case *ssa.UnOp:
 		return c.parseUnOp(frame, expr)
 	default:
@@ -602,8 +664,34 @@ func (c *Compiler) parseConst(expr *ssa.Const) (llvm.Value, error) {
 		strObj := llvm.ConstStruct([]llvm.Value{strLen, strPtr}, false)
 		return strObj, nil
 	case constant.Int:
-		n, _ := constant.Int64Val(expr.Value) // TODO: do something with the 'exact' return value?
-		return llvm.ConstInt(c.intType, uint64(n), true), nil
+		switch expr.Type().(*types.Basic).Kind() {
+		case types.Bool:
+			n, _ := constant.Int64Val(expr.Value)
+			return llvm.ConstInt(llvm.Int1Type(), uint64(n), false), nil
+		case types.Int:
+			n, _ := constant.Int64Val(expr.Value)
+			return llvm.ConstInt(c.intType, uint64(n), false), nil
+		case types.Int8:
+			n, _ := constant.Int64Val(expr.Value)
+			return llvm.ConstInt(llvm.Int8Type(), uint64(n), false), nil
+		case types.Uint8:
+			n, _ := constant.Uint64Val(expr.Value)
+			return llvm.ConstInt(llvm.Int8Type(), n, false), nil
+		case types.Int32:
+			n, _ := constant.Int64Val(expr.Value)
+			return llvm.ConstInt(llvm.Int32Type(), uint64(n), false), nil
+		case types.Uint32:
+			n, _ := constant.Uint64Val(expr.Value)
+			return llvm.ConstInt(llvm.Int32Type(), n, false), nil
+		case types.Int64:
+			n, _ := constant.Int64Val(expr.Value)
+			return llvm.ConstInt(llvm.Int64Type(), uint64(n), false), nil
+		case types.Uint64:
+			n, _ := constant.Uint64Val(expr.Value)
+			return llvm.ConstInt(llvm.Int64Type(), n, false), nil
+		default:
+			return llvm.Value{}, errors.New("todo: unknown integer constant")
+		}
 	default:
 		return llvm.Value{}, errors.New("todo: unknown constant")
 	}