WIP: Initial implementation of optional lens

[baransu]

The basic implementation working for simple cases 🙂

Currently, friendStreetNumber lens compiles but returns an invalid result because we're not accepting enough nested field. With other types, it wouldn't compile.

The optional operator is subject to change but ? is not a valid infix operator and PPX have to be valid Reason if we want to use the AST.

[cem2ran]

Hey @baransu, time flies 😱 Sorry about that!

What do you think about the following two ideas for optional operator:

[%focus person |. department |. address |? street_number]

[%focus person -> department -> address -?> street_number]

|* or -*> would be used for traversal, etc.

[%focus person |. departments |* address |? street_number]

[%focus person -> departments -*> address -?> street_number]

Appears to be valid syntax: https://astexplorer.net/#/gist/8b6189cbc0c84f3678bd45191b93989b/84db4f5e9143e06a62ac675c4c63c515ccf9e1c9