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http://dev.sourcefabric.org/browse/LS-123?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15658#action_15658
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David Baelde commented on LS-123:
---------------------------------
This goes hand in hand with another warning that we don't issue very precisely:
only unit and outputs should be ignored.
For example the other day I wrote the one-line 'input.harbor(%mp3)' and
liquidsoap didn't complain, just said that no output was defined. Stupidly I
thought the harbor input was (incorrectly) not active, but in fact I had just
forgotten the mount parameter, so the application was partial. If this confused
me, it really needs a warning.
The first problem here is that the ignored expression is not in a sequence so
the warning is not issued. The second problem with that warning is that we
don't know statically if a source is active or not, and therefore if it makes
sense to ignore it. One solution I considered is to change all outputs to
(...)->unit instead of (...)->source, but this would make it impossible to pass
an output to functions such as source.id() or source.shutdown(). An obvious
solutions (too simple to be true, there must be something wrong with it) is to
add a subtype of source for outputs, or for active sources in general. We can
perfectly inform the type system about that, it doesn't depend on parameters or
anything as far as I can see.
I think that a subtype for outputs makes more sense: even if it makes sense to
ignore an active input (or something like a strip_blank) it's generally weird.
Then our warning could be issued when something else than unit and outputs is
ignored, and if the subtyping/inference algorithm is not too stupid the same
code as before could be written. (We could even consider outputs as a subtype
of unit, making the warning more uniform but probably more obscure to most
people.)
> Unused variables
> ----------------
>
> Key: LS-123
> URL: http://dev.sourcefabric.org/browse/LS-123
> Project: Liquidsoap
> Issue Type: New Feature
> Components: Liquidsoap
> Reporter: David Baelde
> Assignee: David Baelde
>
> Add a warning for unused variables. This would be useful for users who don't
> understand the let-in style of definitions. One problem is that the warning
> would be issued a lot for utils.liq.
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