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Attribute manipulation helpers

Source: R/ast-attr.R
ast_attr.Rd

[Experimental]

Usage

has_class(x, cls)

add_class(x, cls)

remove_class(x, cls)

get_id(x)

set_id(x, id)

get_attr(x, key)

set_attr(x, ...)

Arguments

x

A pandoc_node (typically one with an @attr slot).

cls

A character vector of class names.

id

A single string.

key

A single string naming an attribute (for get_attr()).

...

For set_attr(), named key = value pairs; each value is a single string, or NULL to remove that key. Quote names that are not syntactic R identifiers (e.g. "data-level" = "2"), and use rlang's !!! / := to supply dynamic keys.

Value

Predicates return a logical scalar (or a string, for getters). Setters return a node of the same class as x.

Details

Concise getters and setters for the pandoc_attr slot found on many pandoc node types (pandoc_header, pandoc_div, pandoc_code, pandoc_link, pandoc_image, pandoc_span, etc.). Modelled on Pandoc Lua filters' direct field access (el.classes, el.identifier, el.attributes) but using R's immutable value semantics: every setter returns a new node, the input is never modified.

Nodes without a standard @attr slot are handled defensively: the getters return FALSE / "" / NA (including nodes such as ordered and bullet lists, whose @attr is a pandoc_list_attributes rather than a pandoc_attr), while setters error with a clear message.

Available helpers

  • has_class(x, cls) TRUE if any of cls is in @attr@classes. When used inside a select_nodes() / map_nodes() predicate, the data-mask version is bound to the current node automatically; the exported version here takes the node as its first argument.

  • add_class(x, cls) add one or more classes (idempotent: classes already present are not duplicated).

  • remove_class(x, cls) remove one or more classes; no-op on classes that are not present.

  • get_id(x) / set_id(x, id) read or replace @attr@id.

  • get_attr(x, key) reads a single attribute, returning NA_character_ for missing keys.

  • set_attr(x, key = value, ...) sets one or more attributes from named key = value pairs. A value of NULL removes that key (the named map's idiomatic R removal, mirroring Lua's el.attributes[key] = nil), so a single call can both set and drop: set_attr(x, target = "_blank", lang = NULL).

Examples

if (FALSE) { # \dontrun{
doc = parse_qmd("# title {.unnumbered}\n")
doc |> map_nodes(is(pandoc_header), .f = function(h) {
  h |> add_class("highlight") |> set_id("intro")
})
} # }