A few months ago, I was similarly confused. Here's what I remember learning since then.
Let's call the character-level syntax of a language *concrete* and any higher-level syntax *abstract*. By these definitions, a *parser* makes concrete syntax abstract, and an *interpreter* translates one piece of abstract syntax into another. In Racket-space, I don't often see concrete and abstract syntax discussed together. We tend to talk exclusively about parsing concrete syntax "into s-expressions," or just assume s-expressions and focus on abstract interpretation of *syntax objects* by *syntax transformers*. I didn't truly "get" syntax transformers until I had a working understanding of the expander and how it affects phase-based execution. I like to think of expansion as term rewriting, with syntax transformers as rewrite rule generators. The expander recursively rewrites the AST at the current phase into the AST for the next phase. This is a fundamentally different perspective than macros as function templates. The paper, *Macros that Work Together*, does a great job explaining the difference. Awareness of the current phase and an ability to re-orient "up" or "down" quickly are now essential skills for my day-to-day macro programming. Intuiting which phase a piece of code inhabits got a lot easier once I internalized the difference between define, define-syntax, and define-for-syntax. When I started with the syntax/parse collection, it was all syntax-parse and define-syntax-class. These days, I'll start with define-simple-macro and increase flexibility -- first to define-syntax-parser, then to syntax-parse inside define-syntax -- as needed. I was pretty comfortable with syntax-case and syntax-rules to begin with, which made picking up the syntax/parse analogues straight forward. Eric On Tue, Aug 7, 2018 at 8:48 AM Alex Gian <alex9...@gmail.com> wrote: > Simply put, I find syntax to be a brain**** > > I can do simple stuff, often by extensive study of example code, and I > even have the odd moment of illumination, which shows me that there is more > to it than just masochism! > > What I do not have is the flow, the mojo, to be able to write syntax like > second nature, and what's more to intersperse it with normal code without > freaking out. > > So I've decided to bite the bullet and dedicate some quality time to the > subject, without constantly winging it. In the light of this, what would > the good folk here recommend as a reasonable path on which to proceed > fairly quickly? I am not averse to meta-anything, but sometimes I just > don't see the elegance that is supposed to be there. > > One of my targets would also be to get the hang of syntax-parse. Are > there any tutorials out there? I do not mind if they are simple. When it > comes to syntax, so am I. > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
