func isTypeLit(t Type) bool {
	switch Unalias(t).(type) {
	case *Named, *TypeParam:
		return false
	}
	return true
}

// isTyped reports whether t is typed; i.e., not an untyped
// constant or boolean.
// Safe to call from types that are not fully set up.
func isTyped(t Type) bool {
	// Alias and named types cannot denote untyped types
	// so there's no need to call Unalias or under, below.
	b, _ := t.(*Basic)

func isTypeLit(t Type) bool {
	switch Unalias(t).(type) {
	case *Named, *TypeParam:
		return false
	}
	return true
}

// isTyped reports whether t is typed; i.e., not an untyped
// constant or boolean.
// Safe to call from types that are not fully set up.
func isTyped(t Type) bool {
	// Alias and named types cannot denote untyped types
	// so there's no need to call Unalias or under, below.
	b, _ := t.(*Basic)

func (check *Checker) recordCommaOkTypes(x syntax.Expr, a []*operand) {
	assert(x != nil)
	assert(len(a) == 2)
	if a[0].mode == invalid {
		return
	}
	t0, t1 := a[0].typ, a[1].typ
	assert(isTyped(t0) && isTyped(t1) && (allBoolean(t1) || t1 == universeError))
	if m := check.Types; m != nil {
		for {
			tv := m[x]
			assert(tv.Type != nil) // should have been recorded already
			pos := x.Pos()
			tv.Type = NewTuple(

func (check *Checker) recordCommaOkTypes(x ast.Expr, a []*operand) {
	assert(x != nil)
	assert(len(a) == 2)
	if a[0].mode == invalid {
		return
	}
	t0, t1 := a[0].typ, a[1].typ
	assert(isTyped(t0) && isTyped(t1) && (allBoolean(t1) || t1 == universeError))
	if m := check.Types; m != nil {
		for {
			tv := m[x]
			assert(tv.Type != nil) // should have been recorded already
			pos := x.Pos()
			tv.Type = NewTuple(

// before any components of e are type-checked.
func (check *Checker) definedType(e syntax.Expr, def *TypeName) Type {
	typ := check.typInternal(e, def)
	assert(isTyped(typ))
	if isGeneric(typ) {
		check.errorf(e, WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
		typ = Typ[Invalid]
	}
	check.recordTypeAndValue(e, typexpr, typ, nil)
	return typ
}

// before any components of e are type-checked.
func (check *Checker) definedType(e ast.Expr, def *TypeName) Type {
	typ := check.typInternal(e, def)
	assert(isTyped(typ))
	if isGeneric(typ) {
		check.errorf(e, WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
		typ = Typ[Invalid]
	}
	check.recordTypeAndValue(e, typexpr, typ, nil)
	return typ
}

		if isParameterized(tparams, par.typ) || isParameterized(tparams, arg.typ) {
			// Function parameters are always typed. Arguments may be untyped.
			// Collect the indices of untyped arguments and handle them later.
			if isTyped(arg.typ) {
				if !u.unify(par.typ, arg.typ, assign) {
					errorf(par.typ, arg.typ, arg)
					return nil
				}
			} else if _, ok := par.typ.(*TypeParam); ok && !arg.isNil() {

		if isParameterized(tparams, par.typ) || isParameterized(tparams, arg.typ) {
			// Function parameters are always typed. Arguments may be untyped.
			// Collect the indices of untyped arguments and handle them later.
			if isTyped(arg.typ) {
				if !u.unify(par.typ, arg.typ, assign) {
					errorf(par.typ, arg.typ, arg)
					return nil
				}
			} else if _, ok := par.typ.(*TypeParam); ok && !arg.isNil() {

	// not compatible, we report a type mismatch error.
	mayConvert := func(x, y *operand) bool {
		// If both operands are typed, there's no need for an implicit conversion.
		if isTyped(x.typ) && isTyped(y.typ) {
			return false
		}
		// An untyped operand may convert to its default type when paired with an empty interface
		// TODO(gri) This should only matter for comparisons (the only binary operation that is

	// not compatible, we report a type mismatch error.
	mayConvert := func(x, y *operand) bool {
		// If both operands are typed, there's no need for an implicit conversion.
		if isTyped(x.typ) && isTyped(y.typ) {
			return false
		}
		// An untyped operand may convert to its default type when paired with an empty interface
		// TODO(gri) This should only matter for comparisons (the only binary operation that is