excluding features from sloppy mode

Claus Reinke claus.reinke at talk21.com
Sun Dec 30 13:59:44 PST 2012

>> It would actually be nice to have that as a feature: If the variable name is
>> `_` then it can be used multiple times. It’s a nice, self-descriptive way of
>> saying that you don’t care about a parameter value.
> That underscore wildcard is the exact syntax used in functional
> languages, and very useful, I agree. In JS, that syntax would be a
> breaking change, unfortunately. But we could use something else (e.g.
> I proposed '.' in the past).

Some languages even interpret any id with '_'-prefix as wildcard, and
warn about uses as likely errors. Btw, the existing duplicate-parameter
error feature smells of should-be-a-warning-not-an-error.

But '_' is in popular use in JS, there being few good short identifiers.

How about moving the early error from parameter list to parameter
use? If a parameter isn't used, even if duplicated, it isn't likely to be
an error (*), and this would allow for wildcard use. If a duplicate
parameter is used at all, that seems to be the case to guard against.


(*) Though one can always construct a case where something is
    an error, eg: function(a,a) { return b } // meant a,b instead of a,a

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