opMixin or mixin function templates with convenience operator?

[Ola Fosheim Grøstad]

On Thursday, 12 December 2019 at 21:40:33 UTC, Paul Backus wrote:
> Is there any actual difference between mixing in a bare 
> expression vs. an immediately-called lambda function that 
> evaluates to the same expression? Forcing string mixins to 
> represent lambdas in particular seems needlessly restrictive.

The idea is to prevent writing to variables outside the mixin. 
So, @pure and const params would perhaps be enough to enable that?