I have recently started porting the reference implementation of GraphQL for JavaScript to Perl, sponsored by Perl Careers. My key considerations:

Use as "modern" Perl as possible: one of the Mo* family, plus type-checking

Follow the JS implementation where it makes sense, but be open to more Perlish ways where that's easier/better

You can see the GitHub repo at https://github.com/graphql-perl/graphql-perl, and the MetaCPAN page for the distro at https://metacpan.org/release/GraphQL.

Initial findings: