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Add lenprefix combinator to pegs.

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This lets peg match n repeitions of a pattern, where
n is supplied from other parsed input and is not a constant.
This commit is contained in:
Calvin Rose
2020-05-02 10:37:39 -05:00
parent 761ea65d81
commit 8b5bcaee3c
4 changed files with 68 additions and 0 deletions
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29
test/suite8.janet
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@@ -252,4 +252,33 @@ neldb\0\0\0\xD8\x05printG\x01\0\xDE\xDE\xDE'\x03\0marshal_tes/\x02
(assert (< [1 2 3] [1 2 3 -1]) "tuple comparison 5")
(assert (> [1 2 3] [1 2]) "tuple comparison 6")
# Lenprefix rule
(def peg (peg/compile ~(* (lenprefix (/ (* '(any (if-not ":" 1)) ":") ,scan-number) 1) -1)))
(assert (peg/match peg "5:abcde") "lenprefix 1")
(assert (not (peg/match peg "5:abcdef")) "lenprefix 2")
(assert (not (peg/match peg "5:abcd")) "lenprefix 3")
# Packet capture
(def peg2
(peg/compile
~{# capture packet length in tag :header-len
:packet-header (* (/ ':d+ ,scan-number :header-len) ":")
# capture n bytes from a backref :header-len
:packet-body '(lenprefix (-> :header-len) 1)
# header, followed by body, and drop the :header-len capture
:packet (/ (* :packet-header :packet-body) ,|$1)
# any exact seqence of packets (no extra characters)
:main (* (any :packet) -1)}))
(assert (deep= @["a" "bb" "ccc"] (peg/match peg2 "1:a2:bb3:ccc")) "lenprefix 4")
(assert (deep= @["a" "bb" "cccccc"] (peg/match peg2 "1:a2:bb6:cccccc")) "lenprefix 5")
(assert (= nil (peg/match peg2 "1:a2:bb:5:cccccc")) "lenprefix 6")
(assert (= nil (peg/match peg2 "1:a2:bb:7:cccccc")) "lenprefix 7")
(end-suite)