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instaparse 2019-11-26
Ahmad 2019-11-26T11:45:37.026Z
@ahmadnazir has joined the channel
Hi, This is related to greedy behavior of instaparse. I have the following grammar:
X := Y* Z*
Y := CHAR
Z := CHAR
CHAR := ('a' | 'b' | 'c')aaa I get the output shown below. I expect greedy behavior and that Y should be matched instead of Z. Does anyone have an idea to why this happens or how to enforce greedy behavior?
aengelberg 2019-12-03T18:35:26.029300Z
@ahmadnazir sorry for the late reply, but instaparse doesn’t guarantee greediness or non-greediness; in fact, if you call insta/parses you will get every version of the parse including ones where Y is parsing some or all of the chars.
Yes, I tried parses and I could see all versions. For some reason I thought there would be a way to prefer one version over the other. Anyway, thanks for the response.
aengelberg 2019-12-03T18:38:02.029700Z
You can achieve greediness by using negative lookahead:
X := Y* !Y Z*👍 1
aengelberg 2019-12-03T18:38:27.029900Z
this ensures that it won’t start parsing Z until it can’t parse Y anymore.