Walk an AST node recursively

Visits every node in a parsed R expression, calling visitor callbacks for calls, symbols, and literals. Findings from callbacks are accumulated and returned.

Usage

walk_ast(expr, visitor, depth = 0L)

Arguments

expr

A language object (from parse_code() or base::parse()).

visitor

A list with optional callback functions:

on_call

function(expr, fn_name, depth) – called for function calls. fn_name is extracted via call_fn_name().

on_symbol

function(expr, name, depth) – called for symbols (names).

on_literal

function(expr, depth) – called for literal values (numeric, character, logical, NULL, etc.).

Each callback should return NULL to continue without accumulating, or any other value to add it to the findings list.

depth

Integer. Current nesting depth (used internally for recursion). Defaults to 0.

Value

A list of findings accumulated from visitor callbacks (excluding NULL returns).

Examples

# Collect all function call names from an expression
expr <- parse_code("mean(x) + sum(y)")[[1]]
visitor <- list(
  on_call = function(expr, fn_name, depth) fn_name
)
walk_ast(expr, visitor)
#> [[1]]
#> [1] "+"
#> 
#> [[2]]
#> [1] "mean"
#> 
#> [[3]]
#> [1] "sum"
#>