Zap source referencesSource:
There are a number of situations where R creates source references:
Reading R code from a file with
parse()might save source references inside calls to
sys.call()includes a source reference if possible.
Creating a closure stores the source reference from the call to
function, if any.
These source references take up space and might cause a number of
zap_srcref() recursively walks through expressions and
functions to remove all source references.