https://github.com/dirkschumacher/defmacro

Load Time R Package Macros
https://github.com/dirkschumacher/defmacro

Last synced: 23 days ago
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Load Time R Package Macros

• Host: GitHub
• URL: https://github.com/dirkschumacher/defmacro
• Owner: dirkschumacher
• License: other
• Created: 2019-09-14T22:03:39.000Z (about 5 years ago)
• Default Branch: master
• Last Pushed: 2022-10-16T13:21:06.000Z (about 2 years ago)
• Last Synced: 2024-08-13T07:15:32.945Z (4 months ago)
• Language: R
• Homepage:
• Size: 28.3 KB
• Stars: 35
• Watchers: 4
• Forks: 2
• Open Issues: 3
• Metadata Files:
  • Readme: README.Rmd
  • License: LICENSE

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• jimsghstars - dirkschumacher/defmacro - Load Time R Package Macros (R)

README

        
---

output: github_document

---

```{r, include = FALSE}

knitr::opts_chunk$set(

  collapse = TRUE,

  comment = "#>",

  fig.path = "man/figures/README-",

  out.width = "100%"

)

```

# defmacro

[![Lifecycle: experimental](https://img.shields.io/badge/lifecycle-experimental-orange.svg)](https://lifecycle.r-lib.org/articles/stages.html#experimental)

[![Codecov test coverage](https://codecov.io/gh/dirkschumacher/defmacro/branch/master/graph/badge.svg)](https://app.codecov.io/gh/dirkschumacher/defmacro?branch=master)

[![CRAN status](https://www.r-pkg.org/badges/version/defmacro)](https://CRAN.R-project.org/package=defmacro)

[![R-CMD-check](https://github.com/dirkschumacher/defmacro/workflows/R-CMD-check/badge.svg)](https://github.com/dirkschumacher/defmacro/actions)

The goal of `defmacro` is to experiment with compile time macros in R.

The idea is to add a macro expansion step during the `.onLoad` step of the package.

A macro is a function that takes code and returns code.

An example package is [here](https://github.com/dirkschumacher/defmacroex).

## Example

For example in a package you define a macro that evaluates an expression at "compile time":

```{r, eval=TRUE}

constexpr <- defmacro::defmacro(function(expr) {

  eval(expr)

})

```

Then you might have a regular function that tests if a value exceeds a quantile of the standard normal distribtion:

```{r}

is_invalid <- function(value) {

  value > constexpr(qnorm(0.975))

}

```

After macro expansion during `.onLoad` the following function is exported to the user:

```{r}

defmacro::expand_function(is_invalid)

```

Thus the call to `qnorm` never happens at runtime as it could have been evaluated during package load.

You could also define your own piping function and have all the overhead removed during runtime:

```{r}

`%>%` <- defmacro::defmacro(function(lhs, rhs) {

  fun_args <- c(list(lhs), unlist(as.list(rhs[-1L]), FALSE))

  rlang::get_expr(rlang::quo(`!!`(rhs[[1L]])(!!!(fun_args))))

})

```

```{r}

analyze_dataset <- function(data) {

  data %>%

    dplyr::filter(hp > constexpr(50 + 50)) %>%

    dplyr::group_by(cyl) %>%

    dplyr::summarise(dplyr::n())

}

```

```{r}

defmacro::expand_function(analyze_dataset)

```

This can also be used to elide parts of your code, akin to `#if` in C:

```{r}

dash_if <- defmacro::defmacro(function(code, condition) {

  if (condition) code

})

```

```{r}

conditional <- function() {

  dash_if(kept(), TRUE)

  dash_if(removed(), FALSE)

}

```

```{r}

defmacro::expand_function(conditional)

```

## Related packages

* [debugme](https://github.com/r-lib/debugme) - Easy and efficient debugging for R packages