[Haskell-beginners] How to nest arbitrary things

[Imants Cekusins]

> a lens with the name 'cans' will be created.

Does Template Haskell modify code file or can these '_' names be used
throughout the code without visible definition?

Thank you for this very detailed and specific example.

Could we say that lens is a bit like extension to record syntax: allow to
traverse, get and set properties for structures that are  more complex than
simple 1 level record?

Why do lens require Template Haskell? Only to generate '_' functions?
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