with_write_flags_lang: Evaluate a language object with write-tracking via active...

In WARDEN: Workflows for Health Technology Assessments in R using Discrete EveNts

Evaluate a language object with write-tracking via active bindings

Description

Temporarily installs active bindings for a set of variable names in env so that any write to those names during the evaluation of expr_lang flips a corresponding ⁠*_lastupdate⁠ flag in env. This flags assignments even when the value is overwritten with the same value, and does not flag branches that are not executed.

Usage

with_write_flags_lang(expr_lang, tracked, env, flag_value = 1L)

Arguments

expr_lang	A language object (call or expression) to evaluate. For example, react_list[[i]][["react"]] returned by add_reactevt().
tracked	Character vector of top-level variable names to track (e.g., c("q_default","c_default","curtime")). For each name nm, an active binding is installed at env[[nm]], and writes set env[[paste0(nm, "_lastupdate")]] <- flag_value.
env	Environment in which to install the bindings and evaluate expr_lang (your per-patient/per-arm working environment).
flag_value	Scalar written into each ⁠*_lastupdate⁠ when a write occurs (commonly 1L; you may use a timestamp like env$curtime).

Details

Typical use: when accum_backwards = TRUE, wrap the evaluation of a reaction/input block so you can later accumulate only inputs that were actually written in that event.

• The function creates a private backing store for tracked names and installs active bindings in env. Reads return the stored value. Writes (via ⁠<-⁠ or =) update the store and set the corresponding ⁠*_lastupdate⁠ flag in env.

• It does not zero the ⁠*_lastupdate⁠ flags; do that before calling this function (typically once per event).

• Only top-level symbols are tracked. To track obj$el <- ..., track "obj" (the container) rather than "obj$el".

• Active bindings are removed and plain symbols restored on exit, even if an error occurs (via on.exit() teardown).

Value

Invisibly returns NULL. The function works by side effects (mutating env and its ⁠*_lastupdate⁠ flags).

Performance

Active bindings add a tiny overhead per read/write of the tracked names (a function call). Keep tracked small and the binding body minimal. Install only for the duration of the block and tear down immediately (handled for you). If your block performs many reads and few writes, consider a snapshot-and-diff approach instead

WARDEN documentation built on Nov. 5, 2025, 7:45 p.m.