0005786: Camlp4 FoldGenerator does not generate visitors for paramatric types

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0005786

OCaml

Camlp4

public

2012-10-12 02:34

2012-10-12 02:54

Reporter

meyer

Assigned To

hongboz

Priority

normal

Severity

feature

Reproducibility

always

Status

acknowledged

Resolution

open

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Fixed in Version

Summary

0005786: Camlp4 FoldGenerator does not generate visitors for paramatric types

Description

type t =
    A of a item
  | B of b item
and 'a item = Item of 'a
and a = string
and b = int

Will fail to generate the visitors with cryptic message similar to:

File "ghost-location", line 1, characters 0-0:
Warning 17: the virtual method unit is not declared.
File "ghost-location", line 1, characters 0-0:
Error: This class should be virtual.
       The following methods are undefined : unit

Additional Information

In order to generate the visitors Camlp4 would need to have type reflection. Simple work-around would be good enough in most cases.

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Notes
(0008244) hongboz (developer) 2012-10-12 02:43	this should be considered as a feature request, since the foldgenerator was quite ad-hoc, and was just used for bootstrapping purpose, it can only handle basic ADT, types like record type, polymorphic variants are not handled well

(0008245) meyer (developer) 2012-10-12 02:53	indeed it's a feature request. I don't neglect how much work is that, and how useful to me is foldgenerator even in current state. I suppose we want something more robust then. I propose the Necula visitors to be close to ideal, implemented in the same way as excellent "deriving" syntax extension.

(0008246) meyer (developer) 2012-10-12 02:54	I'm open to help if it's needed

Issue History
Date Modified	Username	Field	Change
2012-10-12 02:34	meyer	New Issue
2012-10-12 02:34	meyer	Description Updated	View Revisions
2012-10-12 02:35	meyer	Description Updated	View Revisions
2012-10-12 02:43	hongboz	Note Added: 0008244
2012-10-12 02:46	hongboz	Assigned To	=> hongboz
2012-10-12 02:46	hongboz	Severity	minor => feature
2012-10-12 02:46	hongboz	Status	new => acknowledged
2012-10-12 02:53	meyer	Note Added: 0008245
2012-10-12 02:54	meyer	Note Added: 0008246