Cabal: Document the version constraint syntax

[sjakobi]

I was looking for a way to exclude a certain version, and was wondering if there was something like a negation operator. I couldn't find a description of the constraint syntax though.

[23Skidoo]

Try foo < x.y.z || foo > x.y.z.

[23Skidoo]

Related: #4919.

[sjakobi]

Try foo < x.y.z || foo > x.y.z.

Thanks, that's what I ended up using.

A reference would still be great.

[hvr]

@sjakobi http://cabal.readthedocs.io/en/latest/developing-packages.html#pkg-field-build-depends ?

[sjakobi]

Oh, that's what I was looking for! :)

I still can't find it when I use the search term "constraint" in the Read the Docs search.

As most of that section seems to be relevant to other parts of the documentation, like --constraint or build-tool-depends, maybe it should be moved into a separate section "constraint syntax"(?) which can be referenced from the other sections.