.ess_weave <- function(command, file, encoding = NULL){
    cmd_symb <- substitute(command)
    if(grepl('knit|purl', deparse(cmd_symb))) require(knitr)
    od <- getwd()
    on.exit(setwd(od))
    setwd(dirname(file))
    frame <- parent.frame()
    if(is.null(encoding))
        eval(bquote(.(cmd_symb)(.(file))), envir = frame)
    else
        eval(bquote(.(cmd_symb)(.(file), encoding = .(encoding))), envir = frame)
}

.ess_knit <- function(file, output = NULL){
    library(knitr)
    frame <- parent.frame()
    od <- getwd()
    on.exit(setwd(od))
    setwd(dirname(file))
    ## this bquote is really needed for data.table := operator to work correctly
    eval(bquote(knit(.(file), output = .(output))), envir = frame)
}

.ess_sweave <- function(file, output = NULL){
    od <- getwd()
    frame <- parent.frame()
    on.exit(setwd(od))
    setwd(dirname(file))
    eval(bquote(Sweave(.(file), output = .(output))), envir = frame)
}

## Users might find it useful. So don't prefix with .ess.
htsummary <- function (x, hlength = 4, tlength = 4, digits = 3)
{
    ## fixme: simplify and generalize
    snames <- c("mean", "sd", "min", "max", "nlev", "NAs")
    d <- " "
    num_sumr <- function(x){
        c(f(mean(x, na.rm = TRUE)),
          f(sd(x, na.rm = TRUE)),
          f(min(x, na.rm = TRUE)),
          f(max(x, na.rm = TRUE)),
          d,
          f(sum(is.na(x), na.rm = TRUE)))
    }
    f <- function(x) format(x, digits = digits)

    if (is.data.frame(x) | is.matrix(x)) {
        if (nrow(x) <= tlength + hlength){
            print(x)
        } else {
            if (is.matrix(x))
                x <- data.frame(unclass(x))
            ## conversion needed, to avoid problems with derived classes suchs as data.table
            h <- as.data.frame(head(x, hlength))
            t <- as.data.frame(tail(x, tlength))
            for (i in 1:ncol(x)) {
                h[[i]] <- f(h[[i]])
                t[[i]] <- f(t[[i]])
            }
            ## summaries
            sumr <- sapply(x, function(c){
                if(is.logical(c))
                    ## treat logical as numeric; it's harmless
                    c <- as.integer(c)
                if(is.numeric(c))
                    num_sumr(c)
                else if(is.factor(c)) c(d, d, d, d, nlevels(c), sum(is.na(c)))
                else rep.int(d, length(snames))
            })
            sumr <- as.data.frame(sumr)
            row.names(sumr) <- snames
            dots <- rep("...", ncol(x))
            empty <- rep.int(" ", ncol(x))
            lines <- rep.int(" ", ncol(x))
            df <- rbind(h, ...= dots, t, `_____` = lines, sumr, ` ` = empty)
            print(df)
        }
    } else {
        cat("head(", hlength, "):\n", sep = "")
        print(head(x, hlength))
        if(length(x) > tlength + hlength){
            cat("\ntail(", tlength, "):\n", sep = "")
            print(tail(x, tlength))
        }
        cat("_____\n")
        if(is.numeric(x) || is.logical(x))
            print(structure(num_sumr(x), names = snames), quote = FALSE)
        else if(is.factor(x)){
            cat("NAs: ", sum(is.na(x), na.rm = TRUE), "\n")
            cat("levels: \n")
            print(levels(x))
        }
    }
    invisible(NULL)
}

.ess_vignettes <- function(){
    vs <- unclass(browseVignettes())
    vs <- vs[sapply(vs, length) > 0]

    mat2elist <- function(mat){
        if(!is.null(dim(mat))){
            apply(mat, 1, function(r)
                  sprintf("(list \"%s\")",
                          paste0(gsub("\"","\\\\\"",
                                      as.vector(r[c("Title", "Dir", "PDF", "File", "R")])),
                                 collapse = "\" \"")))
        }
    }
    cat("(list \n",
        paste0(mapply(function(el, name) sprintf("(list \"%s\"  %s)", 
                                                 name,
                                                 paste0(mat2elist(el), collapse = "\n")),
                      vs, names(vs)), collapse = "\n"), ")\n")
}