Gentoo Linux includes the Crystal compiler in the main overlay.
You might want to take a look at the available configuration flags first:
# equery u dev-lang/crystal [ Legend : U - final flag setting for installation] [ : I - package is installed with flag ] [ Colors : set, unset ] * Found these USE flags for dev-lang/crystal-0.18.7: U I - - doc : Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally - - examples : Install examples, usually source code + + xml : Use the dev-libs/libxml2 library to enable Crystal xml module + - yaml : Use the dev-libs/libyaml library to enable Crystal yaml module
su - emerge -a dev-lang/crystal
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https://crystal-lang.org/docs/installation/on_gentoo_linux.html