Evaluate an expression and save the result to a file

cached.R

cached <- function (
  file, 
  expr, 
  cache_dir = "cache", 
  compress = "xz", 
  verbose = TRUE, 
  force = FALSE
) {
  file <- normalizePath(file.path(cache_dir, file), mustWork = FALSE)
  if (!file.exists(file) || force) {
    if (verbose) {
      if (force) {
        message("[cached] force:", file)
      } else {
        message("[cached] miss:", file)
      }
    }
    if (!file.exists(dn <- dirname(file))) dir.create(dn, recursive = TRUE)
    saveRDS(obj <- base::force(expr), file = file, compress = compress)
  } else {
    if (verbose) message("[cached] hit:", file)
    obj <- readRDS(file)
  }
  return(obj)
}