node-traversal: Navigate the tree

In astgrepr: Parse and Manipulate R Code

Navigate the tree

Description

This is a collection of functions used to navigate the tree. Some of them have a variant that applies on a single node (e.g. node_next()) and one that applies on a list of nodes (e.g. node_next_all()):

• node_prev(), node_prev_all(), node_next(), and node_next_all() get the previous and next node(s) that are at the same depth as the current node;

• node_parent(), node_ancestors(), node_child() and node_children() get the node(s) that are above or below the current node in terms of depth. All nodes except the root node have at least one node (the root).

Usage

node_parent(x)

node_child(x, nth)

node_ancestors(x)

node_children(x)

node_next(x)

node_next_all(x)

node_prev(x)

node_prev_all(x)

Arguments

x	A node, either from tree_root() or from another ⁠node_*()⁠ function.
nth	Integer. The child node to find. This is 0-indexed, so setting nth = 0 gets the first child.

Value

A node

Examples

### get the previous/next node ---------------------------

src <- "
print('hi there')
a <- 1
fn <- function(x) {
  x + 1
}
"
root <- src |>
  tree_new() |>
  tree_root()

root |>
  node_find(ast_rule(pattern = "a <- $A")) |>
  node_prev() |>
  node_text()

root |>
  node_find(ast_rule(pattern = "a <- $A")) |>
  node_next() |>
  node_text()

# there are nodes inside the function, but there are no more nodes on the
# same level as "fn"
root |>
  node_find(ast_rule(pattern = "a <- $A")) |>
  node_next_all() |>
  node_text_all()


### get the parent/child node ---------------------------

src <- "
print('hi there')
a <- 1
fn <- function(x) {
  x + 1
}
"
root <- src |>
  tree_new() |>
  tree_root()

root |>
  node_find(ast_rule(pattern = "$VAR + 1")) |>
  node_parent() |>
  node_text()

root |>
  node_find(ast_rule(pattern = "$VAR + 1")) |>
  node_ancestors() |>
  node_text_all()

root |>
  node_find(ast_rule(pattern = "$VAR + 1")) |>
  node_child(0) |>
  node_text()

root |>
  node_find(ast_rule(pattern = "$VAR + 1")) |>
  node_children() |>
  node_text_all()

astgrepr documentation built on June 8, 2025, 11:05 a.m.