[Haskell-cafe] template haskell library for OO-like selector syntax?

Matt parsonsmatt at gmail.com
Tue May 15 01:01:48 UTC 2018

You can use `makeFields` from the `lens` package to get something like:

someData ^. field1 . field2

along with modifiers:

someData & field1 . field2 %~ (* 2)

and setters:

someData & field1 . field2 .~ 42

where `field1` is polymorphic and can apply to many different data types

Matt Parsons

On Mon, May 14, 2018 at 6:41 PM, Dennis Raddle <dennis.raddle at gmail.com>

> In my current application, I'm really missing the ability from OO to do
> things like
> someData.field1.field2 = "foo"
> What's do I mean?
> - field selectors are scoped so that names don't clash with each other or
> global names
> - this way of selecting data can be used both for reading it, and for
> updating specific fields of some data deep in a data hierarchy (In Haskell,
> if using immutable data, this would requiring doing a data update on every
> level).
> Any attempt to do this in Haskell, for me anyway, results in an explosion
> of names and a lot of boilerplate code and a resulting heavy syntax.
> Is there a way of obtaining OO-like concise syntax, perhaps with Template
> Haskell?
> Dennis
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