How to use fusen
In fusen: Build a Package from Rmarkdown Files

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)

library(fusen)

All steps to create a package with {fusen} from one Rmd file

Create a new directory / new project with
RStudio template: File > New Project > New directory > Package using {fusen}
Choose the template teaching to start
Or command line: create_fusen("path/to/new/project", template = "teaching")
Open the "dev/flat_teaching" Rmd to start setting up the package
Run the content of the first development chunk with library(testthat) inside
Modify and run the content of the chunk named description asking to describe your package and license it
For the first time, you can let the code as is, this is already the content for a working package
Follow the "dev/flat_teaching.Rmd" template to write your documentation and build your functions and test your examples.
Chunk named function gets the code of a function
Chunk named example gets the code for examples of using the function. This will be used for function @examples and will be kept for the vignette
Chunk named tests gets the code for unit testing
Chunk named development gets the code for development purposes, usually only used once like {usethis} functions
Run the dev-inflate chunk to inflate the flat template and transform it as an inflated package with functions, unit tests and the current Rmd template transformed as a vignette. And check.
Build your {pkgdown} site to verify everything is at the right place

Create multiple "flat_xxx.Rmd" files with fusen::add_flat_template(template = "add") if needed

Fill your package Description

Fonction fill_description() requires the description of your package: What does it do? Who are the developers?
This will fill the DESCRIPTION file in the proper way.

fill_description(
  pkg = dummypackage,
  fields = list(
    Title = "Build A Package From Rmarkdown file",
    Description = paste("Use Rmarkdown First method to build your package.", 
                        "Start your package with documentation.", 
                        "Everything can be set from a Rmarkdown file in your project."),
    `Authors@R` = c(
      person("Sebastien", "Rochette", email = "sebastien@thinkr.fr", 
             role = c("aut", "cre"), comment = c(ORCID = "0000-0002-1565-9313")),
      person(given = "ThinkR", role = "cph")
    )
  )
)

Inflate your package from the flat Rmd template

You're one inflate from flat paper to box. Build your package from the flat Rmd template using the inflate() command below.

After that, you can:

Verify your "DESCRIPTION" file has been updated
Verify your function is in "R/" directory
Verify your test is in "tests/testthat/" directory
Verify this Rmd appears in "vignettes/" directory
Build your documentation using usethis::use_pkgdown() then pkgdown::build() for vignette and examples checks

fusen::inflate(
  flat_file = "dev/flat_teaching.Rmd", 
  vignette_name = "Exploration of my Data",
  open_vignette = TRUE,
  document = TRUE,
  check = TRUE
)

Create a new package from command line directly, using a pre-defined template

Build a package from Rmd template in a temporary directory
This is for testing purposes

# Create a new project
dummypackage <- tempfile(pattern = "dummy")

# {fusen} steps
dev_file <- create_fusen(dummypackage, template = "teaching", open = FALSE)
# Description
fusen::fill_description(pkg = dummypackage, fields = list(Title = "Dummy Package"))

# From inside the package
usethis::with_project(dummypackage, {
  # Define License with use_*_license()
  usethis::use_mit_license("Sébastien Rochette")

  # You may need to execute inflate() in the console directly
  fusen::inflate(pkg = dummypackage, 
                 flat_file = dev_file,
                 vignette_name = "Get started")
})

# Explore directory of the package
browseURL(dummypackage)

# Delete dummy package
unlink(dummypackage, recursive = TRUE)

Add a new "flat_template.Rmd" template in "dev/" directory

# Add an additional dev template
add_flat_template(template = "add", pkg = dummypackage)

There can be development actions

These are only included in the flat template file, their content will not be part of the package anywhere else.

Name the following chunk with {r development-something, eval=FALSE}

```r`r ''`
# Run but keep eval=FALSE to avoid infinite loop

usethis::use_mit_license("Sébastien Rochette")

# Execute in the console directly

fusen::inflate(flat_file = "dev/dev_history.Rmd")
```

Limitations

One title / one chunk is for one function
examples and tests chunks need to be placed after the associated function chunk
You can add sub-functions in the function chunk to store them in the same R file, but they won't have @examples. Only the first function of the chunk will be able to get examples.
As for any Rmarkdown file, chunk names need to be unique. Thus, you better use examples-myfunction, examples-myotherfunction, ...
Do not forget to regularly clear your Workspace to avoid functions hidden by global environment