Environment equivalent of ensuremath

Is there an environment that provides a functionality similar to ensuremath{} (except that I am actually interested in inserting [ … ] instead of ( … ))?

Motivation: I want to define a math-like environment that the user would be able to nest. Thus I want this behavior (simplified example): the environment would create an array environment. If we are not in math mode already, it would enclose it in [ … ]. Because [ … ] cannot be nested, the first sketch of the code:

newenvironment{myenv}{%
  [
  begin{array}{|l}
}{%
  end{array}
  ]%
}

obviously does not work as intended. I cannot do this either:

newenvironment{myenv}{%
  TextOrMath{[}{}
  begin{array}{|l}
}{%
  end{array}
  % Here we are in math mode anyway, so to know when to insert ],
  % we need to remember at which level of nesting we are.
}

So a half-solution would be counting the levels of nesting, which may work in most cases. However, it fails in the (unlikely?) case when a myenv is nested inside text-mode content inside a myenv. To accurately keep track of nesting, we should use a stack. If possible at all with pure (La)TeX, this starts exceeding my TeX skills by far.

makeatletter

  newififsuremath@InText

  newenvironment{suremath}{%
    TextOrMath{%
      % if opening from text context:
      suremath@InTexttrue%
      [%
    }{%
      % if opening from math context:
      suremath@InTextfalse%
    }%
  }{%
    ifsuremath@InText%
      % if closing back to text context:
      ]%
    else%
      % if closing back to math context:
    fi%
  }

makeatother

documentclass{minimal}
newenvironment{suremath}
{ifmmode defendsuremath{}elsedefendsuremath{]}[fi}{}

begin{document}

begin{suremath}
  begin{array}{c}
    a = b x + c  z = u x - v
  end{array}
end{suremath}

begin{equation}
  begin{suremath}
    E = mc^2
  end{suremath}
end{equation}

end{document}