In brodieG/watcher: Watch Function State

How It Works

Let's examine what our earlier watch sum of sequential integers function looks like after watching:

seq_sum_w <- watcher::watch(seq_sum)
seq_sum_w

Each statement is wrapped in brackets, the result is recorded in .res, and state is recorded with capture_data. This is messy as we add the .res symbol to the function environment, and modify the return value by adding attributes to it, but it worked for my purposes. There are other possible implementations, several likely to be cleaner, but this is what fell out of my brain on the first try and it worked so here it is.

Behind the scenes watch also examines the parse data for the function and attempts to line up each top-level statement with the corresponding line of the deparsed function. This is the hackiest part of the process and most likely to fail as it works directly off of the parse data based on my empirical observations of how it behaves. It would be better to work directly off of the srcref data for this, but when I threw this together I didn't quite understand how nested srcref data worked.

If you are interested in instrumenting code in a manner similar to this I strongly encourage you examine the code for [Jim Hester's][1] [covr][2] package rather than this one. I borrowed the rough concept from there, and I have no doubt that implementation is robust, unlike this one.

brodieG/watcher documentation built on Nov. 24, 2019, 12:03 a.m.