opMixin or mixin function templates with convenience operator?

[Ola Fosheim Grøstad]

On Friday, 13 December 2019 at 16:07:01 UTC, Paul Backus wrote:
> You'll notice that there's no direct manipulation of the 
> AST--everything is done by substitution.

Yes, and there are many ways to do substitution.

Full term rewriting is extremely powerful, to the extent that it 
is used for formal proofs and verifiable programming. That is 
going a bit far.

On the other end of the spectrum you have very limited pattern 
matching languages like XSLT that compensate for the simplicity 
by providing entrypoints for scripting (javascript).

So it is possible that something like XSLT (substitution) with 
CTFE where XSLT use javascript could work.

Pattern matching transforms with some CTFE mixed in can provide 
elegant AST manipulation. In my experience it leads to code that 
is relatively easy to read and understand and feels familiar for 
people with FP background.