Migrating dmd to D?

[Zach the Mystic]

On Sunday, 3 March 2013 at 07:27:51 UTC, Daniel Murphy wrote:
>> Now you're as up-to-date as I am on what I'm thinking.
>
> I did something like that before (token-level pattern matching) 
> and found
> the number of special cases to be much much too high.  You need 
> so much
> context information you're better off just building an ast and 
> operating on
> that.

What were the biggest and most common reasons you needed context 
information?