lazyLoad <- function(filebase, envir = parent.frame(), filter)
{
    ##
    ## bootstrapping definitions so we can load base
    ##
    glue <- function (..., sep = " ", collapse = NULL)
        .Internal(paste(list(...), sep, collapse))
    readRDS <- function (file) {
        halt <- function (message) .Internal(stop(TRUE, message))
        gzfile <- function (description, open)
            .Internal(gzfile(description, open, "", 6))
        close <- function (con) .Internal(close(con, "rw"))
        if (! is.character(file)) halt("bad file name")
        con <- gzfile(file, "rb")
        on.exit(close(con))
        .Internal(unserializeFromConn(con, baseenv()))
    }
    "parent.env<-" <-
        function (env, value) .Internal("parent.env<-"(env, value))
    along <- function(x) { n <- length(x); if (n) 1 : n else NULL }
    existsInFrame <- function (x, env) .Internal(exists(x, env, "any", FALSE))
    getFromFrame <- function (x, env) .Internal(get(x, env, "any", FALSE))
    set <- function (x, value, env) .Internal(assign(x, value, env, FALSE))
    environment <- function () .Internal(environment(NULL))
    mkenv <- function() .Internal(new.env(TRUE, baseenv()))
    names <- function(x) .Internal(names(x))
    lazyLoadDBfetch <- function(key, file, compressed, hook)
        .Call("R_lazyLoadDBfetch", key, file, compressed, hook, PACKAGE="base")

    ##
    ## main body
    ##
    mapfile <- glue(filebase, "rdx", sep = ".")
    datafile <- glue(filebase, "rdb", sep = ".")
    env <- mkenv()
    map <- readRDS(mapfile)
    vars <- names(map$variables)
    rvars <- names(map$references)
    compressed <- map$compressed
    for (i in along(rvars))
        set(rvars[i], map$references[[i]], env)
    envenv <- mkenv()
    envhook <- function(n) {
        if (existsInFrame(n, envenv))
            getFromFrame(n, envenv)
        else {
            e <- mkenv()
            set(n, e, envenv)           # MUST do this immediately
            key <- getFromFrame(n, env)
            data <- lazyLoadDBfetch(key, datafile, compressed, envhook)
            parent.env(e) <- data$enclos
            vars <- names(data$bindings)
            for (i in along(vars))
                set(vars[i], data$bindings[[i]], e)
            e
        }
    }
    expr <- quote(lazyLoadDBfetch(key, datafile, compressed, envhook))
    setWrapped <- function(x, value, env) {
    	key <- value			# force evaluation
    	.Internal(delayedAssign(x, expr, environment(), env))
    }
    if (! missing(filter)) {
        for (i in along(vars))
            if (filter(vars[i]))
		setWrapped(vars[i], map$variables[[i]], envir)
    } else {
        for (i in along(vars))
	    setWrapped(vars[i], map$variables[[i]], envir)
    }

    ## reduce memory use **** try some more trimming
    map <- NULL
    vars <- NULL
    rvars <- NULL
    mapfile <- NULL
    readRDS <- NULL
}