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| inner_fn <- function() { | |
| cat("-- Entering Inner Function --\n") | |
| # This step of the body is targeted by `at = 3L` in `trace()` | |
| cat("-- Exiting Inner Function --\n") | |
| return("inner_fn") | |
| } | |
| outer_fn <- function() { | |
| cat("---- Entering Outer Function ----\n") | |
| x <- inner_fn() | |
| cat("---- Exiting Outer Function ----\n") | |
| paste(x, "then outer_fn") | |
| } | |
| outer_fn() | |
| #> ---- Entering Outer Function ---- | |
| #> -- Entering Inner Function -- | |
| #> -- Exiting Inner Function -- | |
| #> ---- Exiting Outer Function ---- | |
| #> [1] "inner_fn then outer_fn" | |
| trace(what = inner_fn, at = 3L, tracer = quote({ | |
| all_frames <- sys.frames() | |
| cur_frame <- all_frames[[sys.nframe()]] | |
| first_to_cur_frame <- min(which(sapply(all_frames, function(f) identical(f, cur_frame)))) | |
| rlang::eval_bare(quote(return("highjacked!")), sys.frames()[[first_to_cur_frame - 1L]]) | |
| })) | |
| #> [1] "inner_fn" | |
| outer_fn() | |
| #> ---- Entering Outer Function ---- | |
| #> -- Entering Inner Function -- | |
| #> Tracing inner_fn() step 3 | |
| #> [1] "highjacked!" | |
| untrace(inner_fn) | |
| outer_fn() | |
| #> ---- Entering Outer Function ---- | |
| #> -- Entering Inner Function -- | |
| #> -- Exiting Inner Function -- | |
| #> ---- Exiting Outer Function ---- | |
| #> [1] "inner_fn then outer_fn" |
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https://twitter.com/yjunechoe/status/1499828109482205184?s=20&t=L0T4EG_o_YN5LJQbMsN5WQ
Created on 2022-03-04 by the reprex package (v2.0.1)