}

func (x *IndexExpr) Pos() token.Pos {
	return x.Orig.Pos()
}

func UnpackIndexExpr(n ast.Node) *IndexExpr {
	switch e := n.(type) {
	case *ast.IndexExpr:
		return &IndexExpr{
			Orig:    e,
			X:       e.X,
			Lbrack:  e.Lbrack,
			Indices: []ast.Expr{e.Index},
			Rbrack:  e.Rbrack,
		}
	case *ast.IndexListExpr:
		return &IndexExpr{
			Orig:    e,
			X:       e.X,

	switch e := n.(type) {
	case *ast.IndexExpr:
		return e.X, e.Lbrack, []ast.Expr{e.Index}, e.Rbrack
	case *ast.IndexListExpr:
		return e.X, e.Lbrack, e.Indices, e.Rbrack
	}
	return nil, token.NoPos, nil, token.NoPos
}

// PackIndexExpr returns an *ast.IndexExpr or *ast.IndexListExpr, depending on
// the cardinality of indices. Calling PackIndexExpr with len(indices) == 0

	"go/internal/typeparams"
	. "internal/types/errors"
)

// If e is a valid function instantiation, indexExpr returns true.
// In that case x represents the uninstantiated function value and
// it is the caller's responsibility to instantiate the function.
func (check *Checker) indexExpr(x *operand, e *typeparams.IndexExpr) (isFuncInst bool) {
	check.exprOrType(x, e.X, true)
	// x may be generic

	switch x.mode {
	case invalid:

	return inst
}

func (check *Checker) callExpr(x *operand, call *syntax.CallExpr) exprKind {
	var inst *syntax.IndexExpr // function instantiation, if any
	if iexpr, _ := call.Fun.(*syntax.IndexExpr); iexpr != nil {
		if check.indexExpr(x, iexpr) {
			// Delay function instantiation to argument checking,
			// where we combine type and value arguments for type
			// inference.

	}
	for _, n := range names {
		if f.Name() == n {
			return true
		}
	}
	return false
}

func funcIdent(fun ast.Expr) *ast.Ident {
	switch fun := astutil.Unparen(fun).(type) {
	case *ast.IndexExpr, *ast.IndexListExpr:
		x, _, _, _ := typeparams.UnpackIndexExpr(fun) // necessary?
		id, _ := x.(*ast.Ident)
		return id
	case *ast.Ident:
		return fun
	default:
		return nil
	}
}

			if n.Type != nil {
				m = n.Type
				continue
			}
			return n.Pos()
		case *KeyValueExpr:
			m = n.Key
		// case *FuncLit:
		// case *ParenExpr:
		case *SelectorExpr:
			m = n.X
		case *IndexExpr:
			m = n.X
		// case *SliceExpr:
		case *AssertExpr:
			m = n.X
		case *TypeSwitchGuard:
			if n.Lhs != nil {
				m = n.Lhs
				continue
			}
			m = n.X
		case *Operation:
			if n.Y != nil {

		n.X = walkExpr(n.X, init)
		return n

	case ir.ODIV, ir.OMOD:
		n := n.(*ir.BinaryExpr)
		return walkDivMod(n, init)

	case ir.OINDEX:
		n := n.(*ir.IndexExpr)
		return walkIndex(n, init)

	case ir.OINDEXMAP:
		n := n.(*ir.IndexExpr)
		return walkIndexMap(n, init)

	case ir.ORECV:
		base.Fatalf("walkExpr ORECV") // should see inside OAS only
		panic("unreachable")

	case ir.OSLICEHEADER:

		a.X = l
		return typecheck.Expr(a)

	case ir.OINDEX, ir.OINDEXMAP:
		n := n.(*ir.IndexExpr)
		var l ir.Node
		if n.X.Type().IsArray() {
			l = o.safeExpr(n.X)
		} else {
			l = o.cheapExpr(n.X)
		}
		r := o.cheapExpr(n.Index)
		if l == n.X && r == n.Index {
			return n
		}
		a := ir.Copy(n).(*ir.IndexExpr)
		a.X = l
		a.Index = r
		return typecheck.Expr(a)

	default:

		left, right = n.X, n.Y
	}

	// Recognize m[k] = append(m[k], ...) so we can reuse
	// the mapassign call.
	var mapAppend *ir.CallExpr
	if left.Op() == ir.OINDEXMAP && right.Op() == ir.OAPPEND {
		left := left.(*ir.IndexExpr)
		mapAppend = right.(*ir.CallExpr)
		if !ir.SameSafeExpr(left, mapAppend.Args[0]) {
			base.Fatalf("not same expressions: %v != %v", left, mapAppend.Args[0])
		}
	}

	left = walkExpr(left, init)

	case *ast.ParenExpr:
		buf.WriteByte('(')
		WriteExpr(buf, x.X)
		buf.WriteByte(')')

	case *ast.SelectorExpr:
		WriteExpr(buf, x.X)
		buf.WriteByte('.')
		buf.WriteString(x.Sel.Name)

	case *ast.IndexExpr, *ast.IndexListExpr:
		ix := typeparams.UnpackIndexExpr(x)
		WriteExpr(buf, ix.X)
		buf.WriteByte('[')
		writeExprList(buf, ix.Indices)
		buf.WriteByte(']')

	case *ast.SliceExpr:
		WriteExpr(buf, x.X)