From 4f225cc740c8fdd3ab597e8e95bbe0887e3dfe08 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Mon, 18 Jun 2018 21:48:30 -0700
Subject: [PATCH] reorder hide & splice (fixes #8)

---
 brag/codegen/runtime.rkt           | 21 ++++++++++++---------
 brag/examples/hide-and-splice.rkt  |  4 ++++
 brag/test/test-all.rkt             |  1 +
 brag/test/test-hide-and-splice.rkt |  9 +++++++++
 4 files changed, 26 insertions(+), 9 deletions(-)
 create mode 100644 brag/examples/hide-and-splice.rkt
 create mode 100755 brag/test/test-hide-and-splice.rkt

diff --git a/brag/codegen/runtime.rkt b/brag/codegen/runtime.rkt
index 7267de1..0182a61 100755
--- a/brag/codegen/runtime.rkt
+++ b/brag/codegen/runtime.rkt
@@ -171,7 +171,7 @@ This would be the place to check a syntax property for hiding.
   (datum->syntax #f d (positions->srcloc start-pos end-pos) stx-with-original?-property))
 
 
-(define (remove-rule-name component-stx [splice #f])
+(define (remove-rule-name component-stx #:splice? [splice #f])
   ;; when removing a rule name, we apply it as a syntax property to the remaining elements
   ;; for possible later usage (aka, why throw away information)   
   (with-syntax ([(name . subcomponents) component-stx])
@@ -191,14 +191,17 @@ This would be the place to check a syntax property for hiding.
    ;; inside `component-stx` is a name followed by subcomponents
    (for*/list ([component-list (in-list component-lists)]
                [component-stx (in-list component-list)]) ; this has the effect of omitting any empty `component-list`
-              (list
-               (cond
-                 [(eq? (syntax-property component-stx 'hide-or-splice) 'hide)
-                  (list (remove-rule-name component-stx))] ; hidden version still wrapped in a sublist
-                 [(or (eq? (syntax-property component-stx 'hide-or-splice) 'splice)
-                      (syntax-property component-stx 'splice-rh-id))
-                  (remove-rule-name component-stx #t)] ; spliced version is lifted out of the sublist
-                 [else (list component-stx)])))))
+     (list
+      (cond
+        ;; test splice first in case both hiding and splicing are set, for instance:
+        ;; /rule : thing @rule
+        ;; otherwise the hide prevents the splice from being expressed
+        [(or (eq? (syntax-property component-stx 'hide-or-splice) 'splice)
+             (syntax-property component-stx 'splice-rh-id))
+         (remove-rule-name component-stx #:splice? #t)] ; spliced version is lifted out of the sublist
+        [(eq? (syntax-property component-stx 'hide-or-splice) 'hide)
+         (list (remove-rule-name component-stx))] ; hidden version still wrapped in a sublist
+        [else (list component-stx)])))))
 
 
 ;; rule-components->syntax: (U symbol false) (listof stx) ... #:srcloc (U #f (list src line column offset span)) -> stx
diff --git a/brag/examples/hide-and-splice.rkt b/brag/examples/hide-and-splice.rkt
new file mode 100644
index 0000000..e1e422d
--- /dev/null
+++ b/brag/examples/hide-and-splice.rkt
@@ -0,0 +1,4 @@
+#lang brag
+top : x | y
+/x : Ø | "x" @x
+@y : Ø | "y" y
\ No newline at end of file
diff --git a/brag/test/test-all.rkt b/brag/test/test-all.rkt
index 578eefb..58e326d 100755
--- a/brag/test/test-all.rkt
+++ b/brag/test/test-all.rkt
@@ -10,6 +10,7 @@
          "test-empty-symbol.rkt"
          "test-errors.rkt"
          "test-flatten.rkt"
+         "test-hide-and-splice.rkt"
          "test-lexer.rkt"
          "test-old-token.rkt"
          "test-parser.rkt"
diff --git a/brag/test/test-hide-and-splice.rkt b/brag/test/test-hide-and-splice.rkt
new file mode 100755
index 0000000..17d19e4
--- /dev/null
+++ b/brag/test/test-hide-and-splice.rkt
@@ -0,0 +1,9 @@
+#lang racket/base
+(require brag/examples/hide-and-splice
+         brag/support
+         rackunit)
+
+;; check that an id with both a splice and hide is handled correctly
+
+(check-equal? (parse-to-datum "xxx") '(top ("x" "x" "x")))
+(check-equal? (parse-to-datum "yyy") '(top "y" "y" "y"))
\ No newline at end of file