[x] I have added tests to demonstrate the contribution is correctly implemented: this usually includes both positive and negative tests, showing the happy path(s) and featuring intentionally broken cases
[x] I have run all the tests locally and no test failure was reported
[x] I have run the linter, formatter and spellchecker
[x] I did not do unrelated and/or undiscussed refactorings
This simplifies the grammar and typechecking and makes error messages more user-friendly
Closes #440 (also partially addresses #377, namely field accesses)