Why doesn't the AST define an instance for `Eq`?

[ivanperez-keera]

I just noticed that the AST does not define an instance for Eq.

It would be useful to be able to compare AST branches for equality (for example, to ensure you are not generating the same expression twice, or to be able to put declarations in a set). Is there a fundamental reason why it cannot or should not be done
?

[fdedden]

No, there should not be a specific reason for omitting the Eq instance. So far there never was a need for it.

We can add the instance, and probably add it for language-c99 as well.