An introduction to styler

Lorenz Walthert

2019-10-17

This vignette introduces the basic functionality of styler and showcases how styler applies a few rules of the tidyverse style guide to example code. Note that you can create your own style guide and customize styler even further, as described in the vignette “Customizing styler”.

It’s possible to use different levels of ‘invasiveness’, as described in the help file for the only style guide implemented so far, which is the tidyverse style guide. The style guide in use is passed to the styling function (i.e style_text() and friends) via the style argument, which defaults to tidyverse_style. In addition to this argument, there are further customization options. For example, we can limit ourselves to styling just spacing information by indicating this with the scope argument:

library("styler")
library("magrittr")
style_text("a=3; 2", scope = "spaces")

a = 3; 2

Or, on the other extreme of the scale, styling spaces, indention, line breaks and tokens (which is the default):

style_text("a=3; 2", scope = "tokens")

a <- 3
2

scope always includes less-invasive styling than the option chosen, e.g. spaces = "line_breaks" includes styling spaces and indention in addition to line breaks.

We can also choose to style line breaks but not tokens:

style_text("if(x) {66 } else {a=3}", scope = "line_breaks")

if (x) {
  66
} else {
  a = 3
}

Note that scope = "spaces" does not touch indention

code <- c(
    "a <- function() { ", 
    "                a=3", 
    "}"
)

style_text(code, scope = "spaces")

a <- function() {
                a = 3
}

But scope = "indention" - as the name says - does.

style_text(code, scope = "indention")

a <- function() {
  a = 3
}

Another option that is helpful to determine the level of ‘invasiveness’ is strict. If set to TRUE, spaces and line breaks before or after tokens are set to either zero or one. However, in some situations this might be undesirable, as the following example shows:

style_text(
  "data_frame(
     small  = 2 ,
     medium = 4,#comment without space
     large  = 6
   )", strict = FALSE
)

data_frame(
  small  = 2,
  medium = 4, # comment without space
  large  = 6
)

We prefer to keep the equal sign after “small”, “medium” and large aligned, so we set strict = FALSE to set spacing to at least one around =.

Also, spaces before comments are preserved with that option.

style_text(
  "a <-   'one'   #just one
   abc <- 'three' # three", 
  strict = FALSE
)

a <-   "one"   # just one
abc <- "three" # three

Though simple, hopefully the above examples convey some of the flexibility of the configuration options available in styler. Let us for now focus on a configuration with strict = TRUE and scope = "tokens" and illustrate a few more examples of code before and after styling.

styler can identify and handle unary operators and other math tokens:

# Before
1++1-1-1/2

# After
1 + +1 - 1 - 1 / 2

This is tidyverse style. However, styler offers very granular control for math token spacing. Assuming you like spacing around + and -, but not around / and * and ^, do the following:

style_text(
  "1++1/2*2^2", 
  math_token_spacing = specify_math_token_spacing(zero = c("'/'", "'*'", "'^'"))
)

1 + +1/2*2^2

It can also format complicated expressions that involve line breaking and indention based on both brace expressions and operators:

# Before
if (x >3) {stop("this is an error")} else {
c(there_are_fairly_long,
1 / 33 * 
2 * long_long_variable_names)%>% k(

) }

# After
if (x > 3) {
  stop("this is an error")
} else {
  c(
    there_are_fairly_long,
    1 / 33 *
      2 * long_long_variable_names
  ) %>% k()
}

Lines are broken after ( if a function call spans multiple lines:

# Before
do_a_long_and_complicated_fun_cal("which", has, way, to, 
                              "and longer then lorem ipsum in its full length"
                              )

# After
do_a_long_and_complicated_fun_cal(
  "which", has, way, to,
  "and longer then lorem ipsum in its full length"
)

styler replaces = with <- for assignment:

# Before
one = "one string"

# After
one <- "one string"

It converts single quotes within strings if necessary:

# Before
one <- 'one string'
two <- "one string in a 'string'"

# After
one <- "one string"
two <- "one string in a 'string'"

And adds braces to function calls in pipes:

# Before
a %>%
  b %>%
  c

# After
a %>%
  b() %>%
  c()

Function declarations are indented if multi-line:

# Before
my_fun <- function(x, 
y, 
z) {
  just(z)
}

# After
my_fun <- function(x,
                   y,
                   z) {
  just(z)
}

styler can also deal with tidyeval syntax:

# Before
mtcars %>%
  group_by( !!my_vars )

# After
mtcars %>%
  group_by(!!my_vars)

If you, say, don’t want comments starting with ### to be indented, you can formulate an unindention rule:

style_text(
  c(
    "a <- function() {",
    "### not to be indented",
    "# indent normally",
    "33",
    "}"
  ),
  reindention = specify_reindention(regex_pattern = "###", indention = 0)
  
)

a <- function() {
### not to be indented
  # indent normally
  33
}