% outer binds exprs -> env_new -> new_env
/env_new { 3 dict begin
    %(in env_new\n) print
    /exprs exch dup _sequential? { /data get }{ pop [ ] } ifelse def
    /binds exch dup _sequential? { /data get }{ pop [ ] } ifelse def
    /outer exch def
    << 
        /__outer__ outer
        0 1 binds length 1 sub {
            /idx exch def
            binds idx get (&) eq { %if &
                binds idx 1 add get % key
                exprs idx   exprs length idx sub   getinterval % value
                _list_from_array
                exit
            } if
            binds idx get % key
            exprs idx get % value
        } for
    >>
end } def

/env_set { % env key value ->
    put
} def

/env_get { % env key -> value true    OR    false
    {
        2 copy known { get true exit } if
        exch /__outer__ get
        dup null eq { pop pop false exit } if
        exch
    } loop
} def