R/write_model.R

In bstaton1/codaTools: Utilities for Processing Posterior Samples Stored in 'mcmc.lists'

#' @title Export BUGS/JAGS model from function to file
#' @description Performs the same basic function as [R2OpenBUGS::write.model()]
#' @param fun A function object containing BUGS/JAGS model code
#' @param file A character vector of length == 1: the name of the file to write to
#' @details Performs the same basic function as [R2OpenBUGS::write.model()],
#'   but with slightly better output (scientific notation, spacing, etc.). The main reason it was created
#'   for use in 'postpack' was to remove the need for using the 'R2OpenBUGS' package when not using OpenBUGS.
#' @return Nothing, but `file` is written to disk.
#' @examples
#' if (interactive()) {
#'   # define some simple BUGS model as an R function
#'   # note the use of %_% to include a truncation
#'   mod = function() {
#'     # PRIORS
#'     mu ~ dnorm(0,0.001) %_% T(0,)
#'     sig ~ dunif(0,10)
#'     tau <- 1/sig^2
#'
#'     # LIKELIHOOD
#'     for (i in 1:n) {
#'       y[i] ~ dnorm(mu, tau)
#'     }
#'   }
#'
#'   # write model to a text file to be called by BUGS/JAGS
#'   write_model(mod, "model.txt")
#' }
#' @export

write_model = function(fun, file) {

  # error check
  if (!is.function(fun)) {
    stop("'fun' must be a function object")
  }

  # extract the body
  model_body = body(fun)
  model_body = as.character(model_body)
  model_body = model_body[-1]

  # remove all %_% instances
  model_body = stringr::str_replace_all(model_body, "%_%", "")

  # split on new lines
  model_body = unlist(stringr::str_split(model_body, "\n"))

  # reduce the number of spaces used for indenting: this is super hacky
  model_body = stringr::str_replace_all(model_body, stringr::fixed("    "), "  ")
  model_body = stringr::str_replace_all(model_body, stringr::fixed("      "), "    ")
  model_body = stringr::str_replace_all(model_body, stringr::fixed("        "), "      ")
  model_body = stringr::str_replace_all(model_body, stringr::fixed("          "), "        ")
  model_body = stringr::str_replace_all(model_body, stringr::fixed("            "), "          ")
  model_body = stringr::str_replace_all(model_body, stringr::fixed("              "), "            ")
  model_body = stringr::str_replace_all(model_body, stringr::fixed("                "), "              ")

  # add in a constant indent to all lines
  model_body = paste0("  ", model_body)

  # add the first and last lines
  model = c("model {", model_body, "}")

  # write the model to file
  writeLines(model, file)
}