Hello, I cannot open a ticket on the website due to an error OperationalError: could not extend file "base/19263/19289": No space left on device HINT: Check free disk space. Anyway, I found a bug in the library. The file is mpl/preprocessed/boost_mpl_preprocess.py a script that creates the headers required to have more than 50 types on a template. Basically the problem is on the string substitutions, with some values the output is wrong. I made a pull request that fixes the problem making a temporary substitution of the values https://github.com/boostorg/mpl/pull/29