[Caml-list] recursive values of abstract types, aka Batteries ParserCo

["Christoph Höger" <christoph.hoeger@tu-berlin.de>]

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Hi all,

I wanted to parse a small lambda-calculus in OCaml and had batteries
already as a dependency. Batteries comes with ParserCo, a small parser
combinator library. Since I did not want to complicate things further,
I decided to stick with it and avoid any parser generator. Using a
monadic combinator library for a scannerless parser should be a
relatively simple exercise, right?

Unfortunately, it seems that ParserCo only exposes an abstract type:

type ('a, 'b, 'c) t

which is, of course, a function:

type ('a, 'b, 'c) t = ('a, 'c) Source.t -> ('a, 'b, 'c) result

This prevents me from defining any recursive parsers, since OCaml
won't let me let-rec a value of an abstract function type. I cannot do
eta-expansion, because the type is abstract, and I also do not have a
type constructor at hand.

How does one handle such cases in OCaml? Does this really mean, you
cannot have recursive values of abstract function types?

thanks,

Christoph



- -- 
Christoph Höger

Technische Universität Berlin
Fakultät IV - Elektrotechnik und Informatik
Übersetzerbau und Programmiersprachen

Sekr. TEL12-2, Ernst-Reuter-Platz 7, 10587 Berlin

Tel.: +49 (30) 314-24890
E-Mail: christoph.hoeger@tu-berlin.de
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