These functions return children of x by field id or name.
node_child_by_field_id()retrieves a child by field id.node_child_by_field_name()retrieves a child by field name.
Use language_field_id_for_name() to get the field id for a field name.
Arguments
- x
[tree_sitter_node]A node.
- id
[integer(1)]The field id of the child to return.
- name
[character(1)]The field name of the child to return.
Examples
language <- treesitter.r::language()
parser <- parser(language)
text <- "fn <- function() { 1 + 1 }"
tree <- parser_parse(parser, text)
node <- tree_root_node(tree)
# Navigate to first child
node <- node_child(node, 1)
node
#> <tree_sitter_node>
#>
#> ── Text ──────────────────────────────────────────────────────────────────
#> fn <- function() { 1 + 1 }
#>
#> ── S-Expression ──────────────────────────────────────────────────────────
#> (binary_operator [(0, 0), (0, 26)]
#> lhs: (identifier [(0, 0), (0, 2)])
#> operator: "<-" [(0, 3), (0, 5)]
#> rhs: (function_definition [(0, 6), (0, 26)]
#> name: "function" [(0, 6), (0, 14)]
#> parameters: (parameters [(0, 14), (0, 16)]
#> open: "(" [(0, 14), (0, 15)]
#> close: ")" [(0, 15), (0, 16)]
#> )
#> body: (braced_expression [(0, 17), (0, 26)]
#> open: "{" [(0, 17), (0, 18)]
#> body: (binary_operator [(0, 19), (0, 24)]
#> lhs: (float [(0, 19), (0, 20)])
#> operator: "+" [(0, 21), (0, 22)]
#> rhs: (float [(0, 23), (0, 24)])
#> )
#> close: "}" [(0, 25), (0, 26)]
#> )
#> )
#> )
# Get the field name of the first child
name <- node_field_name_for_child(node, 1)
name
#> [1] "lhs"
# Now get the child again by that field name
node_child_by_field_name(node, name)
#> <tree_sitter_node>
#>
#> ── Text ──────────────────────────────────────────────────────────────────
#> fn
#>
#> ── S-Expression ──────────────────────────────────────────────────────────
#> (identifier [(0, 0), (0, 2)])
# If you need to look up by field name many times, you can look up the
# more direct field id first and use that instead
id <- language_field_id_for_name(language, name)
id
#> [1] 11
node_child_by_field_id(node, id)
#> <tree_sitter_node>
#>
#> ── Text ──────────────────────────────────────────────────────────────────
#> fn
#>
#> ── S-Expression ──────────────────────────────────────────────────────────
#> (identifier [(0, 0), (0, 2)])
# Returns `NULL` if no matching child
node_child_by_field_id(node, 10000)
#> NULL