New option for sum codecs: mapTag

[m-bock]

In a nutshell:

data Sample
  = Foo
  | Bar Int
  | Baz Boolean String Int

with a codec

codecSample :: JsonCodec Sample
codecSample = sumWith opts

opts = EncodeTagged
  { tagKey: "tag"
  , valuesKey: "values"
  , omitEmptyArguments: true
  , unwrapSingleArguments: true
  , mapTag: Str.toLower -- <----------------- new option
  }

will encode/decode this JSON:

{
  "tag": "baz",
  "values": [true, "hello", 42]
}

Tests added, also implemented for for other encodings like "nested" and "flat".

[wclr]

This is a useful addition. Although it is not type-safe in terms of input values (sum type tag names), which would be useful for tags migration or some other specific cases.

[garyb]

I wondered about that too, I thought about suggesting a dimap type thing instead, but actually I really like this approach. Anything more involved than a structure preserving mapping could be handled through a migration codec instead I think.