Unused value warning on a recursive value that is used #7429
Comments
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Comment author: @alainfrisch
Another workaround is to remove the useless declaration altogether, no? |
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Comment author: @lpw25 The point is that the declaration is not useless. The |
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Comment author: @alainfrisch But how is 'subscribe' being executed if 'x' is not forced? |
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Comment author: @lpw25 Oh wait, my example is actually useless. I'll have another look at the original code it comes from and see if it can be made into a sensible example. |
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Comment author: @lpw25 Ok, I've had a look at the original code and it seems that it would not compile. It was equivalent to: let rec x = subscribe (fun _ -> x);; The confusion seems to have come from the fact that you get the warning about it being unused before you get the error about it not compiling. So basically the warning is overly aggressive, but only on programs that are inappropriately recursive. In which case, this bug report is just a duplicate of the general complaint that recursion errors are handled after type-checking. |
Original bug ID: 7429
Reporter: @lpw25
Assigned to: @lpw25
Status: resolved (set by @lpw25 on 2016-12-07T16:12:59Z)
Resolution: not a bug
Priority: normal
Severity: minor
Version: 4.04.0
Category: typing
Related to: #6738
Monitored by: @gasche
Bug description
The following code:
let rec x = lazy (subscribe (fun _ -> (Lazy.force x)));;
produces an unused value warning for
xif it is not used in the rest of the program. However, the binding toxis required in this case.Obviously, the warning is trying to make sure that things like recursive function definitions do not get automatically marked as used just because they are recursive, but it seems that the issue is subtler than how the current check works.
This code is pretty unusual, and the work-around is easy (simply rename
xto_x) so it may not be worth fixing if the criteria is too complicated.The text was updated successfully, but these errors were encountered: