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Address #641 - add undef combinator.

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The (undef rule :tag) combinator lets a user "scope" tagged captures.
After the rule has matched, all captures with tag :tag can no longer be
refered to by their tag. However, such captures from outside
rule are kept as is. If no tag is given, all tagged captures from rule
are unreferenced. Note that this doesn't `drop` the captures, merely
removes their association with the tag. This means subsequent calls to
`backref` and `backmatch` will no longer "see" these tagged captures.
This commit is contained in:
Calvin Rose
2021-02-26 17:25:09 -06:00
parent a5f237993d
commit 96513665d6
3 changed files with 46 additions and 4 deletions
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12
test/suite0003.janet
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@@ -481,4 +481,16 @@
(check-deep '(to "b") "aaaa" nil)
(check-deep '(thru "b") "aaaa" nil)
# unref
(def grammar
(peg/compile
~{:main (* :tagged -1)
:tagged (unref (replace (* :open-tag :value :close-tag) ,struct))
:open-tag (* (constant :tag) "<" (capture :w+ :tag-name) ">")
:value (* (constant :value) (group (any (+ :tagged :untagged))))
:close-tag (* "</" (backmatch :tag-name) ">")
:untagged (capture (any (if-not "<" 1)))}))
(check-deep grammar "<p><em>foobar</em></p>" @[{:tag "p" :value @[{:tag "em" :value @["foobar"]}]}])
(check-deep grammar "<p>foobar</p>" @[{:tag "p" :value @["foobar"]}])
(end-suite)