Add benchmarks or tests with 'inspection-testing' tool

There's such line in documentation:

> Also, when optimisation is turned on, GHC will compile them to the same code.

Would be good to be sure in such things. Probably some benchmarks or even tests with `inspection-testing` tool could help this!

Duplicates: https://github.com/reinerp/first-class-patterns/issues/4

Start by locating the documentation containing the claim that optimization produces the same code, then review the `inspection-testing` tool and the duplicate issue at https://github.com/reinerp/first-class-patterns/issues/4. Done means adding benchmarks or tests that verify the claim.

Written by the indexing model from the issue text.