diff --git a/.Rbuildignore b/.Rbuildignore
index 0e754c0..e8fbf40 100644
--- a/.Rbuildignore
+++ b/.Rbuildignore
@@ -3,4 +3,5 @@
 ^examples
 ^\.travis\.yml$
 ^appveyor\.yml$
+R/TODO.txt
 ^.RData
diff --git a/DESCRIPTION b/DESCRIPTION
index 0a2e7b0..96c1e62 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -16,7 +16,9 @@ LazyData: true
 Imports:
     V8 (>= 0.6),
     jsonlite,
-    utils
+    utils,
+    R6
+Enhances: lumberjack
 URL: http://github.com/edwindj/daff
 Suggests:
     testthat
diff --git a/NAMESPACE b/NAMESPACE
index eab5b03..20994b2 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -6,12 +6,14 @@ S3method(print,data_diff_summary)
 S3method(summary,data_diff)
 export(diff_data)
 export(differs_from)
+export(lbj_daff)
 export(merge_data)
 export(patch_data)
 export(read_diff)
 export(render_diff)
 export(which_conflicts)
 export(write_diff)
+import(R6)
 importFrom(V8,JS)
 importFrom(V8,new_context)
 importFrom(jsonlite,toJSON)
diff --git a/R/lumberjack.R b/R/lumberjack.R
new file mode 100644
index 0000000..0944e22
--- /dev/null
+++ b/R/lumberjack.R
@@ -0,0 +1,114 @@
+# A logger for the 'lumberjack' package.
+
+
+
+#' Automatically derive daffs with the lumberjack package
+#'
+#' The lbj_daff logger creates a \code{daff} and writes it to \code{daff<n>.csv}
+#' in a directory of choice.
+#'
+#' @import R6
+#'
+#' @section Creating a logger:
+#'
+#' \code{filedump$new(dir=file.path(tempdir(),"daff")
+#'    , prefix="step\%03d.csv", verbose=TRUE, ...)}
+#' \tabular{ll}{
+#'   \code{dir}\tab Where to write the daff files.\cr
+#'   \code{filename}\tab filename template, used with \code{\link{sprintf}}
+#'      to create a file name.\cr
+#'   \code{verbose}\tab toggle verbosity\cr
+#'   \code{...}\tab Extra arguments, passed to \code{diff_data} each time.
+#' }
+#'
+#' @section Dump options:
+#'
+#' \code{$dump(...)}
+#' \tabular{ll}{
+#'   \code{...}\tab Currently unused.\cr
+#' }
+#'
+#' @section Retrieve log data:
+#'
+#' \code{$logdata(simplify=TRUE)} returns a list of data frames, sorted in the
+#'   order returned by \code{base::dir()}
+#' \code{$diffs(simplify=TRUE)} returns a list of \code{daff} objects, sorted
+#'   in the order returned by \code{base::dir()}
+#'
+#' \tabular{ll}{
+#' \code{simplify}\tab Simplify lists of length 1 to data.frame?
+#' }
+#'
+#' @section Details:
+#'
+#' If \code{dir} does not exist it is created. If
+#'
+#'
+#' @docType class
+#' @format An \code{R6} class object.
+#'
+#' @examples
+#' \dontrun{
+#'  library(lumberjack)
+#'  logger <- lbj_daff$new()
+#'  women %>>%
+#'    start_log(logger) %>>%
+#'    head() %>>%
+#'    {. * 2} %>>%
+#'    dump_log()
+#'  L <- logger$logdata()
+#'  L[[2]]
+#'  L <- logger$diffs()
+#'  L[[1]]
+#' }
+#'
+#' @family loggers
+#' @export
+lbj_daff <- R6Class("lpj_daff"
+  , public=list(
+    n = NULL
+    , dir = NULL
+    , verbose = NULL
+    , filename = NULL
+    , daff_args = NULL
+    , initialize = function(dir = file.path(tempdir(), "daff")
+       , filename="daff%03d.csv", verbose = TRUE,...){
+      self$n <- 0
+      self$dir <- dir
+      if (!dir.exists(dir)){
+        dir.create(dir,recursive = TRUE)
+        if (verbose){
+          msgf("Created %s", normalizePath(dir))
+        }
+      }
+      self$verbose <- verbose
+      self$filename <- filename
+      self$daff_args <- list(...)
+    }
+    , add = function(meta, input, output){
+        outname <- file.path(self$dir,sprintf(self$filename,self$n))
+        self$n <- self$n + 1
+        outname <- file.path(self$dir, sprintf(self$filename,self$n))
+        arglist <- c(list(data_ref=input, data=output), self$daff_args)
+        output <- do.call("diff_data", arglist)
+        write_diff(output, file=outname)
+    }
+    , dump = function(...){
+        if ( self$verbose ){
+          msgf("daffs were written to %s", normalizePath(self$dir))
+        }
+    }
+   , logdata = function(simplify=TRUE){
+      fl <- dir(self$dir,full.names = TRUE)
+      L <- lapply(fl, function(x) read_diff(x)$get_data())
+      if (simplify && length(L) == 1L) L[[1]] else L
+   }
+   , diffs = function(simplify=TRUE){
+      fl <- dir(self$dir, full.names=TRUE)
+      L <- lapply(fl, read_diff)
+      if (simplify && length(L) == 1L) L[[1]] else L
+   }
+))
+
+# msgf: the reasonable messenger :^)
+msgf <- function(fmt,...) message(sprintf(fmt,...))
diff --git a/man/lbj_daff.Rd b/man/lbj_daff.Rd
new file mode 100644
index 0000000..386e7c4
--- /dev/null
+++ b/man/lbj_daff.Rd
@@ -0,0 +1,73 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/lumberjack.R
+\docType{class}
+\name{lbj_daff}
+\alias{lbj_daff}
+\title{Automatically derive daffs with the lumberjack package}
+\format{An \code{R6} class object.}
+\usage{
+lbj_daff
+}
+\description{
+The lbj_daff logger creates a \code{daff} and writes it to \code{daff<n>.csv}
+in a directory of choice.
+}
+\section{Creating a logger}{
+
+
+\code{filedump$new(dir=file.path(tempdir(),"daff")
+   , prefix="step\%03d.csv", verbose=TRUE, ...)}
+\tabular{ll}{
+  \code{dir}\tab Where to write the daff files.\cr
+  \code{filename}\tab filename template, used with \code{\link{sprintf}}
+     to create a file name.\cr
+  \code{verbose}\tab toggle verbosity\cr
+  \code{...}\tab Extra arguments, passed to \code{diff_data} each time.
+}
+}
+
+\section{Dump options}{
+
+
+\code{$dump(...)}
+\tabular{ll}{
+  \code{...}\tab Currently unused.\cr
+}
+}
+
+\section{Retrieve log data}{
+
+
+\code{$logdata(simplify=TRUE)} returns a list of data frames, sorted in the
+  order returned by \code{base::dir()}
+\code{$diffs(simplify=TRUE)} returns a list of \code{daff} objects, sorted
+  in the order returned by \code{base::dir()}
+
+\tabular{ll}{
+\code{simplify}\tab Simplify lists of length 1 to data.frame?
+}
+}
+
+\section{Details}{
+
+
+If \code{dir} does not exist it is created. If
+}
+
+\examples{
+\dontrun{
+ library(lumberjack)
+ logger <- lbj_daff$new()
+ women \%>>\%
+   start_log(logger) \%>>\%
+   head() \%>>\%
+   {. * 2} \%>>\%
+   dump_log()
+ L <- logger$logdata()
+ L[[2]]
+ L <- logger$diffs()
+ L[[1]]
+}
+
+}
+\keyword{datasets}
diff --git a/tests/testthat/test_lumberjack.R b/tests/testthat/test_lumberjack.R
new file mode 100644
index 0000000..ee74341
--- /dev/null
+++ b/tests/testthat/test_lumberjack.R
@@ -0,0 +1,14 @@
+
+context("lumberjack logger")
+
+test_that("lumberjack logger",{
+  logger <- lbj_daff$new()
+  meta=list(expr=expression({.*2}), src="{\n .*2\n}")
+  logger$add(meta, women, 2*women)
+  expect_equal(logger$n,1L)
+  fl <- dir(logger$dir, full.names = TRUE)
+  expect_equal(length(fl),1L)
+  d <- read.csv(fl)
+  expect_equal(nrow(d), nrow(women)*ncol(women))
+  expect_equal(nrow(logger$logdata()), nrow(women)*ncol(women))
+})