Support more literal classes

[countvajhula]

Summary of Changes

This adds support for more literal classes: vectors, boxes and (maybe) prefabs.

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[countvajhula]

I attempted to support prefab literals the same way as the others:

diff --git a/qi-lib/flow/aux-syntax.rkt b/qi-lib/flow/aux-syntax.rkt
index b47bb86..cf4604f 100644
--- a/qi-lib/flow/aux-syntax.rkt
+++ b/qi-lib/flow/aux-syntax.rkt
@@ -19,6 +19,7 @@
          expr:byte-regexp
          expr:vector-literal
          expr:box-literal
+         expr:prefab-literal
          ;; We'd like to treat quoted forms as literals as well. This
          ;; includes symbols, and would also include, for instance,
          ;; syntactic specifications of flows, since flows are
@@ -45,6 +46,9 @@
 (define-syntax-class box-literal
   (pattern #&v))

+(define-syntax-class prefab-literal
+  (pattern #s(_ ...)))
+
 (define-syntax-class (starts-with pfx)
   (pattern i:id
     #:when (string-prefix?
diff --git a/qi-test/tests/flow.rkt b/qi-test/tests/flow.rkt
index d79efce..580a0e1 100644
--- a/qi-test/tests/flow.rkt
+++ b/qi-test/tests/flow.rkt
@@ -49,6 +49,7 @@
      (check-equal? ((flow #(1 2 3)) 2) #(1 2 3) "literal vector")
      (check-equal? ((flow #&3) 2) #&3 "literal box")
      (check-equal? ((flow #&(1 2 3)) 2) #&(1 2 3) "literal collection in a box")
+     (check-equal? ((flow #s(dog "Fido")) 2) #s(dog "Fido") "literal prefab")
      (check-equal? ((flow '(+ 1 2)) 5) '(+ 1 2) "literal quoted list")
      (check-equal? ((flow `(+ 1 ,(* 2 3))) 5) '(+ 1 6) "literal quasiquoted list")
      (check-equal? (syntax->datum ((flow #'(+ 1 2)) 5)) '(+ 1 2) "Literal syntax quoted list"))

But this doesn't work, with the error:

raco setup:   qi-lib/flow/aux-syntax.rkt:53:16: pattern: pattern keyword not allowed here
raco setup:     at: ...
raco setup:     in: (pattern #s(_ ...))

It doesn't like #s(_ ...). From the docs for the prefab syntax pattern, it looks like the pattern expects a specific prefab-struct-key (like dog) and not a generic pattern like _. So, I'm not sure if it would be possible to match arbitrary prefabs using this approach.

[benknoble]

LGTM. I agree that the prefab patterns require a literal prefab struct key, which kind of makes sense: mentioning a prefab by writing #s(cat "tom") is enough to create such a prefab structure type with a single field (entirely distinct from #s(cat "tom" black)—also note the implicit quoting).

Perhaps there's a way to inspect the syntax and determine if it's a prefab struct literal? I see that prefab-struct-key is #f if the argument is not a prefab instance, so perhaps some version of #:when (prefab-struct-key (syntax-e #'the-possibly-literal-expr))?

[countvajhula]

Great points. And that totally worked 😃 The tests are failing now due to the bindingspec name change, but that I verified locally that it works when the updated dependency name and syntax is used.