Macro r

Source

r!() { /* proc-macro */ }

Expand description

Evaluate R code written as Rust tokens, validated at compile time.

r! takes a single R expression as a token stream, stringify!s it into a static R source string at build time, and evaluates it via [miniextendr_api::expression::r_eval_str] (the same protect-safe parse + eval path as r_str!).

§What you get today

Because the argument is a Rust token tree, the Rust front-end already rejects unbalanced delimiters (r!(f(1, 2) won’t compile) and lexically invalid tokens before R ever sees the string — a cheap compile-time guard over the pure-runtime r_str!. The source is lowered to a &'static str (stringify!), so there is no format! allocation at the call site.

This proc-macro additionally validates a conservative subset of known-bad R syntax constructs (trailing binary operators, consecutive non-unary binary operators, bare if/while/for without a body, etc.) and emits a precise compile error pointing at the offending token. Empty (missing) call arguments — f(, x), matrix(, 2, 2) — are valid R and pass.

§What is deferred

Direct Rf_lang* call-tree lowering (skipping the runtime parser entirely) is tracked as a follow-up in issue #938 (item 2). Until then r! parses its static string at first evaluation, exactly like r_str!.

§Non-goals

A complete R grammar validator is not achievable over Rust tokens:

Single-quoted strings ('hello') and backtick-quoted names (`foo`) already die at the Rust lexer — nothing to validate.
%op% tokenises as %, ident, % and is accepted without analysis.
Anything the validator cannot confidently classify as wrong passes through unvalidated (conservative reject-only-known-bad design).

§Forms

r!(R tokens…) — evaluate in R_GlobalEnv.
r!(env: e; R tokens…) — evaluate in the environment SEXP e. The leading env: <expr> ; is consumed as Rust, the rest is R source.

Both evaluate to Result<SEXP, String>; the SEXP is unprotected.

§Safety

Expands to an unsafe block; the underlying FFI is #[r_ffi_checked], so calls from a worker thread are serialized onto the R thread.

§Example

let three = r!(1L + 2L)?;
let rows = r!(getFromNamespace(".theoph_rows", "dataframeflows")())?;
let in_env = r!(env: my_env; x + 1)?;

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