Search and rewrite R source code by syntax using astgrepr. Use when asked to find patterns in code, search for function calls, identify usage of specific arguments, locate structural patterns across R files, or perform find-and-replace on code structure.
{astgrepr} enables AST-based code search — structural queries that regex can't express cleanly.
If not installed: install.packages("astgrepr")
library(astgrepr)
src <- "
add <- function(x, y) x + y
greet <- function(name, greeting, sep) paste0(greeting, sep, name)
square <- function(x) x^2
"
root <- src |> tree_new() |> tree_root() # or tree_new(file = "R/Foo.R")
# µNAME/µA/µB capture matched nodes; only `add` matches (2 params)
matches <- node_find_all(root,
ast_rule(id = "two_arg", pattern = "µNAME <- function(µA, µB) µBODY")
)
matches #> <List of 1 rule> |--two_arg: 1 nodes
node_text_all(matches) # source text of each match
lapply(matches$two_arg, \(n) node_get_match(n, "NAME") |> node_text()) #> "add"
Metavariables: µVAR captures one node (uppercase only); µµµ captures zero or more (ellipsis). In replacement strings, refer to captures as .
~~VAR~~ast_rule() — see ?ast_rule. Key args:
pattern — code pattern with metavariableskind — tree-sitter node kind; see the R grammarregex — match node text with a Rust regexid — names the rule; results accessible as matches$idinside, has, precedes, follows — relational rules, each takes another ast_rule()all, any, not — boolean combinators, each takes a list of ast_rule()sFor advanced pattern syntax: ast-grep pattern docs.
lapply(list.files("R", pattern = "\\.R$", full.names = TRUE), \(f) {
root <- tree_root(tree_new(file = f))
texts <- node_find_all(root, ast_rule(id = "r", pattern = "YOUR_PATTERN")) |>
node_text_all() |> _$r
if (length(texts) > 0) list(file = basename(f), matches = texts)
}) |> Filter(Negate(is.null), x = _)
ast_rule(pattern = "if (µµµ) { return(µµµ) } else µµµ") # if-else with return()
ast_rule(pattern = "util_fun(debug = µµµ)") # named argument
ast_rule(kind = "while_statement") # by node kind
ast_rule(pattern = "df$µCOL") # df$col, any column
ast_rule(pattern = "print(µA)", # relational: inside loop
inside = ast_rule(any = ast_rule(kind = c("for_statement", "while_statement"))))
ast_rule(any = list(ast_rule(pattern = "any(is.na(µµµ))"), # boolean OR
ast_rule(pattern = "any(duplicated(µµµ))")))
See ?node_replace_all, ?tree_rewrite.
root <- tree_root(tree_new(file = "R/MyFile.R"))
fixes <- root |>
node_find_all(
ast_rule(id = "any_na", pattern = "any(is.na(µVAR))"),
ast_rule(id = "any_dup", pattern = "any(duplicated(µVAR))")
) |>
node_replace_all(any_na = "anyNA(~~VAR~~)",
any_dup = "anyDuplicated(~~VAR~~) > 0")
tree_rewrite(root, fixes) # preview
writeLines(tree_rewrite(root, fixes), con = "R/MyFile.R") # write back