You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: struct_matcher.go
    path of file: ./repos/cerbos/internal/engine/planner/matchers
    
    the code of the file until where you have to start completion: // Copyright 2021-2024 Zenauth Ltd.
// SPDX-License-Identifier: Apache-2.0

package matchers

import (
	"errors"
	"sort"

	"github.com/cerbos/cerbos/internal/engine/planner/internal"
	"github.com/google/cel-go/common/operators"
	exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
)

type exprMat
    
func NewExpressionProcessor() ExpressionProcessor {
	s1 := new(structMatcher)
	s1.rootMatch = &exprMatcher{
		f: func(e *exprpb.Expr) (res bool, args []*exprpb.Expr) {
			if ce := e.GetCallExpr(); ce != nil && len(ce.Args) == 2 {
				if _, ok := supportedOps[ce.Function]; ok {
					s1.function = ce.Function
					return true, ce.Args
				}
			}
			return false, nil
		},
		ns: []*exprMatcher{
			getStructIndexerExprMatcher(s1),
			getConstExprMatcher(s1),
		},
	}
	s2 := new(structMatcher)
	s2.rootMatch = &exprMatcher{
		f: func(e *exprpb.Expr) (res bool, args []*exprpb.Expr) {
			if ce := e.GetCallExpr(); ce != nil && len(ce.Args) == 2 && ce.Function == operators.In {
				s2.function = ce.Function
				return true, ce.Args
			}
			return false, nil
		},
		ns: []*exprMatcher{
			getConstExprMatcher(s2),
			getStructIndexerExprMatcher(s2),
		},
	}

	return processors([]ExpressionProcessor{s1, s2})
}