Dear List! THis MWE must be faulty, but where is the error? ==================================================== \startluacode userdata = userdata or {} function userdata.file_exists (name) local name = name local f = assert ( io.open ( name, "r" )) if f then f:close () context ( name ) context ( " exists!" ) else context ( name ) context ( " doesn't exist!" ) end end \stopluacode \starttext \def\lookupfile#1% {\ctxlua{userdata.file_exists([==[#1]==])}} \lookupfile{"$HOME/context-tests/AAA.lua"} % "AAA.lua" intentionally does exist \lookupfile{"$HOME/context-tests/BBB.lua"} % "BBB.lua" intentionally doesn't exist \stoptext ==================================================== It makes no difference in commenting out the first or the second "\lookupfile" command. The error message eventually is always nearly the same: token call, execute: [ctxlua]:8: "$HOME/context-tests/AAA.lua": No such file or directory token call, execute: [ctxlua]:8: "$HOME/context-tests/BBB.lua": No such file or directory I'm using: LuaMetaTeX, Version 2.00.0 ConTeXt ver: 2019.10.10 18:15 MKIV beta fmt: 2019.10.12 int: english/english Please, any ideas? Regards, Rudolf