Fix outdated code examples

[JulianGCalderon]

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This PR fixes some outdated code examples.

The following examples are still failing, because support for them has yet not been implemented:

• examples/factorial.con
• examples/union.con

What should we do with these files? Should we move them to another directory examples/unimplemented?

Also, the example examples/check_error.con fails, but given its name maybe its on purpose. Should be move it another directory examples/failing?