Within puppet-syntax there's functionality to validate .epp files. Currently this uses internal Puppet API's, but using a formal API in PAL would be more future proof.
Quoting Henrik Lindberg from https://github.com/voxpupuli/puppet-syntax/pull/108#issuecomment-538759867 [quote] I do think PAL should support EPP as well with functionality for parse, validate, and evaluate just like for regular manifests. [/quote]