Convert an R object to YAML

This function is used internally when validating S7schema objects, and when using write_config() to save a configuration.

Underneath it is calling yaml::as.yaml() to do the conversion, but all logical values are converted to true/false instead of yes/no respectively for a more robust integration with other YAML parsers. Date values are written as ISO 8601 strings ("2025-08-06"), and numbers are written with precision = 15 instead of the default of 7. Numbers with up to 16 significant digits are read back as the same value, while numbers that need 17, e.g. 0.1 + 0.2, are rounded.

Missing values are written as:

• logical NA as .na

• NA_character_ as .na.character

• NA_integer_ as .na.integer

• NA_real_ as .na.real

R reads all of them back as NA, while other YAML parsers read them as strings. Previously logical NA was written as NA, which R read back as the string "NA".

It is rarely relevant to call this function directly except for debugging purposes, or when implementing a new method for your own object class.

Usage

to_yaml(x)

Arguments

x

object to convert to YAML.

Value

character(1) YAML string.

Details

to_yaml() dispatches based on the class of x. Register a new S7 method if you want to overwrite how your own class is converted to YAML. See S7::method() for more information.

The default method uses yaml::verbatim_logical() to overwrite the default behavior of handling logical values, and a handler for Date values. The logical handler writes NA as .na, so it is read back as NA:

function(x) {
  yaml::as.yaml(
    x = x,
    precision = 15,
    handlers = list(
      logical = \(x) {
        x <- yaml::verbatim_logical(x)
        x[is.na(x)] <- ".na"
        x
      },
      Date = \(x) format(x, "%Y-%m-%d")
    )
  )
}

Copy this and add your own additional handlers when implementing a new method.

Examples

# Convert simple list to YAML
to_yaml(list(hello = "world", is_today = TRUE)) |>
  cat()
#> hello: world
#> is_today: true

# Missing logical values are written as .na
to_yaml(list(a = NA, b = c(TRUE, NA))) |>
  cat()
#> a: .na
#> b:
#> - true
#> - .na

# Convert S7schema object
x <- S7schema(
  file = system.file("examples/config.yml", package = "S7schema"),
  schema = system.file("examples/schema.json", package = "S7schema")
)

print(x)
#> <S7schema::S7schema> List of 1
#>  $ my_config_var: int 1
#>  @ schema   : chr "/home/runner/work/_temp/Library/S7schema/examples/schema.json"
#>  @ validator: <S7schema::validator>
#>  .. @ context:List of 6
#>  .. .. $ context :<pointer: 0x64209004db70> 
#>  .. .. $ validate:function (code_string)  
#>  .. .. $ source  :function (file = NULL, code = NULL)  
#>  .. .. $ call    :function (function_name, ...)  
#>  .. .. $ get     :function (var_name)  
#>  .. .. $ assign  :function (var_name, value)  
#>  .. .. - attr(*, "class")= chr "JSContext"
#>  @ file     : chr "/home/runner/work/_temp/Library/S7schema/examples/config.yml"

to_yaml(x) |>
  cat()
#> my_config_var: 1