[perl] Shared error and expression tests

[ehuelsmann]

Description

Refactor the code to comply with the shared tests for expressions and errors.

Motivation & context

Consistency across implementations.

Type of change

• Refactoring/debt (improvement to code design or tooling without changing behaviour)

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• I have added tests to cover my changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

[ehuelsmann]

@aslakhellesoy The Perl implementation has a different internal representation, which causes differences in the "parsing.yml" output: the "and" and "or" operators are "lispy" in the sense that they accept as many operands as you provide, resulting in:

# Failed test 'Stringified parser for \\x or y\\ or z\\'
# at t/03-shared-tests.t line 63.
# +-----------------------+----+---------------------------+
# | GOT                   | OP | CHECK                     |
# +-----------------------+----+---------------------------+
# | ( \\x or y\\ or z\\ ) | eq | ( ( \\x or y\\ ) or z\\ ) |
# +-----------------------+----+---------------------------+

Although I do see the point in the parsing.yml tests (and I found it helpful in discovering that '' is defined to return true always), I'm wondering if running these should be more than a developer's tool to inspect that the reported differences have no semantic impact.

[ehuelsmann]

Actually, I just figured out how to compensate the difference without changing the internal representation.

[aslakhellesoy]

Very nice @ehuelsmann! These shared acceptance tests seem to come in handy :-)

[ehuelsmann]

Very nice @ehuelsmann! These shared acceptance tests seem to come in handy :-)

Absolutely. They give me the confidence that we present the same API across implementations.