How to invoke shell function in string? (bash)

I want to invoke shell function in string. Here is my use case:

function envfoo() {
    env ENV_FOO=foo $@
}
function envbar() {
    env ENV_BAR=bar $@
}

$ envfoo env |egrep ENV_
ENV_FOO=foo
$ envbar env |egrep ENV_
ENV_BAR=bar
$ envfoo envbar env |egrep ENV_
env: envbar: No such file or directory
# expected result: ENV_FOO=foo and ENV_BAR=bar lines

Here I want envfoo to execute envbar shell function. How can I do it?

Say that is opposite of command which ignores shell function and finds real command.

Maybe I gave a wrong example. I want to combine multiple shell functions like actual executables. A real case goes like this:

function be() {
    bundle exec $@
}

function envstg() {
    env RAILS_ENV=staging $@
}

$ be rails server
# launches Rails server

$ envstg be rails server
env: be: No such file or directory

Here be isn't expanded into bundle exec. How can I expand them?