> On Dec 20, 2016, at 12:59 AM, Daniel Prager <daniel.a.pra...@gmail.com> wrote:
>
> This isn't too bad, but What I'd *really* like is a "string-match" form to
> more elegantly process structured data, via a few strings based on a simple
> (and greedy) left-to-right algorithm.
>
> But my macro-fu is too weak.
>
> 1. Can someone show me how to write this style of macro?
> 2. Is this of more general interest?
IIRC Alex Knauth's `match-string` package does what you want.
But vanilla syntax patterns will match strings and numbers literally, and thus
arguably amount to a "simple (and greedy) left-to-right algorithm".
#lang racket
(require (for-syntax racket/string))
(define-syntax (sm stx)
(syntax-case stx ()
[(_ "whole-string") #''whole]
[(_ str) (with-syntax ([TOKS (string-split (syntax->datum #'str)
#px"--|\\s")])
#'(sm . TOKS))]
[(_ X1 X2 X3 "end") #'(list (string->symbol X1) (string->number X2) X3)]
[(_ "the" ANIMAL "is" COLOR) #'(string-join (list COLOR ANIMAL) " ")]
[else #''no-match-found]))
(sm "abc--123 foo end") ;-> '(abc 123 "foo")
(sm "the fox is black") ;-> "black fox"
(sm "whole-string") ;-> 'whole
(sm "abc--123--456 bar end") ;-> 'no-match-found ; greedy strategy keeps things
simple and explicit
The tokenizer stashed in the second case is a little shameful. If you were
making a DSL it would be cleaner to put that part in the reader, and then `sm`
could omit that case.
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