Fieldslib syntax extension usage | Real World OCaml

[synco...@gmail.com]

Hi, I was reading Real World OCaml, and I am stuck at First-Class Fields [1]. The "with fields" syntax is no longer working as it appears in the book. As far as I can tell, the fieldslib was originally inside core, but is now a separate package. 

I tried reading the .mli file at https://github.com/janestreet/fieldslib/blob/master/src/field.mli, but I can't seem to figure out what the code means or how to use the fieldslib package. 

[1]

https://realworldocaml.org/v1/en/html/records.html#first-class-fields

[Yaron Minsky]

RWO really needs a refresh (for which I have plans brewing...)

With the arrival of PPX, Core and friends no longer use the old
camlp4-based syntax extensions. If you install the new PPX versions
(which are installed by opam when you install Core), you can use the
now-standardized "deriving syntax", e.g.:

type r = { foo:int; bar: float} [@@deriving fields]

to get the same effect you would have gotten with:

type r = { foo:int; bar: float} with fields

in the old world.

y

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[syn copy]

I see. Thanks for the quick reply!