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camlp4: camlp4r: exception equal to another exception #5301

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vicuna opened this issue Jun 26, 2011 · 2 comments
Closed

camlp4: camlp4r: exception equal to another exception #5301

vicuna opened this issue Jun 26, 2011 · 2 comments

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@vicuna
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@vicuna vicuna commented Jun 26, 2011

Original bug ID: 5301
Reporter: Dmitry Grebeniuk
Assigned to: @xclerc
Status: closed (set by @xavierleroy on 2012-09-25T18:06:17Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 3.13.0+dev
Category: -for Camlp4 use https://github.com/ocaml/camlp4/issues

Bug description

Maybe I'm trying to use the wrong syntax, but the error message should be more readable.

$ ocaml
OCaml version 3.13.0+dev3

#use "topfind";;

[..]

#camlp4r;;

[..]

module A = struct exception E of int; end;

module A : sig exception E of int; end

exception Q of int = A.E;

Assertion failed, file "camlp4/Camlp4/Struct/Camlp4Ast2OCamlAst.ml", line 948, char 21

@vicuna
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@vicuna vicuna commented Jun 28, 2011

Comment author: @xclerc

The fix is temporary because it drops the type information provided at aliasing site.
The actual type is taken from the original exception without checking that it is the
same that is provided by the alias.

@vicuna
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@vicuna vicuna commented Jul 12, 2011

Comment author: @xclerc

After consultation of the AST for the original grammar,
and discussion with Nicolas Pouillard, it turns out that
the syntactic construct has to be disallowed.

Indeed, when aliasing an exception in the original syntax,
there is not way to "repeat" its type. As camlp4 has no type
information, it cannot do more than the original syntax.
Hence, the decision to forbid the syntactic construct.

However, you will now be presented a (hopefully) much
nicer error message.

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