Debugging Tools to Inspect the Intermediate Steps of a Call.

boomer

The {boomer} package provides debugging tools that let you inspect the intermediate results of a call. The output looks as if we explode a call into its parts hence the name.

• boom() prints the intermediate results of a call or a code chunk.
• rig() creates a copy of a function which will display the intermediate results of all the calls of it body.
• rig_in_namespace() rigs a namespaced function in place, so its always verbose even when called by other existing functions. It is especially handy for package development.

Installation

Install CRAN version with:

install.packages("boomer")

Or development version with:

remotes::install_github("moodymudskipper/boomer")

boom()

library(boomer)
boom(1 + !1 * 2)

boom(subset(head(mtcars, 2), qsec > 17))

You can use boom() with {magrittr} pipes or base R pipes: just pipe to boom() at the end of a pipe chain.

library(magrittr)
mtcars %>%
  head(2) %>%
  subset(qsec > 17) %>%
  boom()

If a call fails, {boomer} will print intermediate outputs up to the occurrence of the error, it can help with debugging:

"tomato" %>%
  substr(1, 3) %>%
  toupper() %>%
  sqrt() %>%
  boom()

boom() features optional arguments :

• clock: set to TRUE to see how long each step (in isolation!) took to run.

• print: set to a function such as str to change what is printed (see ?boom to see how to print differently depending on class). Useful alternatives would be dplyr::glimpse of invisible (to print nothing).

One use case is when the output is too long.

boom(lapply(head(cars), sqrt), clock = TRUE, print = str)

boom() also works works on loops and multi-line expression.

 boom(for(i in 1:3) paste0(i, "!"))

rig()

rig() a function in order to boom() its body, its arguments are printed by default when they’re evaluated.

hello <- function(x) {
  if(!is.character(x) | length(x) != 1) {
    stop("`x` should be a string")
  }
  paste0("Hello ", x, "!")
}
rig(hello)("world")

rig_in_namespace()

rig() creates a copy of a function, but when developing a package we might want to rig a function in place so it has a verbose output when called by other functions. For this we can use rig_in_namespace().

For instance you might have these functions in a package :

cylinder_vol <- function(r, h) {
  h * disk_area(r)
}

disk_area <- function(r) {
  pi * r^2
}

cylinder_vol depends on disk_area, call devtools::load_all() then rig_in_namespace() on both and enjoy the detailed output:

devtools::load_all()
rig_in_namespace(cylinder_vol, disk_area)
cylinder_vol(3,10)

boom_on() and boom_off()

While debugging a function, call boom_on() and all subsequent calls will be boomed, call boom_off() to return to standard debugging.

boom_shinyApp()

A very experimental feature that allows you to rig the reactives of a shiny app. See vignette("shiny", "boomer") for more information.

For the following app, saved in a proper project/package:

histogramUI <- function(id) {
  tagList(
    selectInput(NS(id, "var"), "Variable", choices = names(mtcars)),
    numericInput(NS(id, "bins"), "bins", value = 10, min = 1),
    plotOutput(NS(id, "hist"))
  )
}

histogramServer <- function(id) {
  moduleServer(id, function(input, output, session) {
    data <- reactive(mtcars[[input$var]])
    output$hist <- renderPlot({
      hist(data(), breaks = input$bins, main = input$var)
    }, res = 96)
  })
}

ui <- fluidPage(
  histogramUI("hist1")
)
server <- function(input, output, session) {
  histogramServer("hist1")
}

The output of boom_shinyApp(ui, server) will look like:

There will be issues, please report!

Addin

To avoid typing boom() all the time you can use the provided addin named “Explode a call with boom()”: just attribute a key combination to it (I use ctrl+shift+alt+B on windows), select the call you’d like to explode and fire away!

Options

Several options are proposed to weak he printed output of {boomer}’s functions and addin, see ?boomer to learn about them.

In particular on some operating systems {boomer}’s functions’ output might not always look good in markdown report or reprexes. It’s due to how he system handles UTF-8 characters. In this case one can use options(boomer.safe_print = TRUE) for a more satisfactory input.

Notes

{boomer} prints the output of intermediate steps as they are executed, and thus doesn’t say anything about what isn’t executed, it is in contrast with functions like lobstr::ast() which return the parse tree.

Thanks to @data_question for suggesting the name {boomer} on twitter.