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: expr.go
    path of file: ./repos/cointop/vendor/github.com/antonmedv/expr
    
    the code of the file until where you have to start completion: package expr

import (
	"fmt"
	"github.com/antonmedv/expr/ast"
	"github.com/antonmedv/expr/file"
	"reflect"

	"github.com/antonmedv/expr/checker"
	"github.com/antonmedv/expr/compiler"
	"github.com/anton
    
func Eval(input string, env interface{}) (interface{}, error) {
	if _, ok := env.(Option); ok {
		return nil, fmt.Errorf("misused expr.Eval: second argument (env) should be passed without expr.Env")
	}

	tree, err := parser.Parse(input)
	if err != nil {
		return nil, err
	}

	program, err := compiler.Compile(tree, nil)
	if err != nil {
		return nil, err
	}

	output, err := vm.Run(program, env)
	if err != nil {
		return nil, err
	}

	return output, nil
}