DIP 50 - AST macros

[Walter Bright]

On 11/14/2013 11:40 AM, deadalnix wrote:
> This is not proposing to configure syntax.

Right, it is about inserting arbitrarily different meaning into existing syntax.

For example, I have a friend from the middle east who worked at Microsoft. His 
english was excellent. But sometimes he'd get tripped up - for example, he'd 
take his idea to his boss, who'd discuss it, and then say:

     "fine"

He took that to mean "my boss approves of my great idea!" Unfortunately, "fine" 
has undergone a meaning reversal colloquially, and actually means "your idea 
sux". This wound up getting him into trouble. There were a few other phrases 
like this with unintentionally hilarious misunderstandings.

(Also, a popular way of encrypting communications is to have private meanings 
for phrases like "my cat ate my homework" meaning "initiate Operation X".)

Now, let's take the AST macros, and pass it "4+3". Apparently is a feature that 
the macro can transform this to produce "hello" as the result. The result is 
that although the language looks the same, there is no "anchor" a person can 
rely on to indicate the meaning. The meaning of "fine" is reversed, so to speak.

The riposte is, of course, every feature can be abused and good programmers 
won't do that. Unfortunately, it's IN THE VERY NATURE of macros to be abusive, 
and even the very best programmers can and will take it to the limit. They will 
see and decry the abuse in everyone else's code but their own, which they will 
justify. As I said, I see this over and over again.

On the other hand, with string mixins, it is immediately obvious that one is 
dealing with different syntax, and so expect something different to happen.