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Pack interpolate -- prolog/interpolate.pl
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 $interpolate_macro_sentinel
Nothing to see here. This is an implementation detail to avoid unwanted string interpolation. Because string interpolation is implemented as a macro and macro expansion is done through a predicate with gloabl reach (term_expansion/2), we must take precautions to avoid performing string interpolation on code that doesn't want it. Importing this predicate opts-in to string interpolation. Writing use_module(library(interpolate)) does it for you.