Questions about the Lark parser project
Use this tag when asking questions about the Lark parser project (https://github.com/lark-parser/lark)
Questions tagged [lark-parser]
97 questions
1
vote
2 answers
Lark matching custom delimiter multiline strings
I am trying to use lark to extract some information from perl files. For that, I need a basic understanding of what a statement is. The issue I came across are "Here Document" strings. I would describe them as multiline strings with custom…
user766308
- 103
- 7
1
vote
1 answer
Getting next possible tokens with lark parsing
I wanted to know if there is a way to get the next possible token of a given string and a given grammar with lark parsing.
For example if I have the grammar.
?start: NAME "=" possible_values
possible_values: "apple" | "banana" | "orange"
and I…
Pablo Estrada
- 3,182
- 4
- 30
- 74
1
vote
1 answer
How to add a small bit of context in a grammar?
I am tasked to parse (and transform) a code of a computer language, that has a slight quirk in its rules, at least I see it this way. To be exact, the compiler treats new lines (as well as semicolons) as statement separators, but other than that…
Jock Tanner
- 70
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- 8
1
vote
1 answer
Lark : how to pick only some patterns
I would like to extract from a text file only some structured patterns.
example, in the text below:
blablabla
foo FUNC1 ; blabliblo blu
I would like to isolate only 'foo FUNC1 ;'.
I was trying to use lark parser with the following…
Pierre G.
- 4,346
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1
vote
0 answers
How to implement lookaheads in Lark?
I'm currently looking at the work done to write the Python 3.8 grammar with Lark, and I'm wondering how that can be done with the Python 3.9 grammar specification which looks a bit simpler to me. Note that I'm not sure of whether my approach…
PatW
- 141
- 5
1
vote
1 answer
How can I split a rule with Lark EBNF?
I'm writing a grammar for parsing PlantUML State diagrams and have the following doubt:
I had:
transition: STATE arrow STATE (":" event? guard? action?)? "\n"
arrow: ("->" | "-->" | "-left->" | "-right->" | "-up->" | "-down->")
But had to change…
Toni Homedes i Saun
- 638
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- 15
1
vote
1 answer
Beginner Question: "No terminal defined for 'i' at line 2 col 1 int "i" 10" Lark
I am very new to lark and am trying to create a simple parser, but I am getting suck on a seemingly simple quesion, why does "No terminal defined for 'i' at line 2 col 1 int "i" 10" show up? Here is my grammar:
start: set_str
|…
Asra
- 151
- 1
- 11
1
vote
0 answers
How to match opening and closing tags in Lark?
I'm trying to create a parser using Lark for WordPress shortcodes. The self-closing tags in the language have no differentiating features from standard opening tags, causing a fair bit of ambiguity even in perfectly valid syntax. I've got it mostly…
A.Gudek
- 11
- 2
1
vote
1 answer
Lark Parser raising error when evaluating print statement after if/else statement
so I'm making a programming language using python and the lark library for parsing. When I'm parsing the following
if 5 == 4 {
print("TRUE");
}
else {
print("FALSE");
}
print("Done!");
It raises the following error
PS E:\ParserAndLexer> &…
Rayyan Cyclegar
- 59
- 2
- 6
1
vote
1 answer
Parse trailing line comments with lark and LALR
Given are the following lark grammar and Python source code:
start: (TEXT _NEWLINE)+
TEXT: /[^\n]+/
COMMENT: /\/\/[^\n]*/ _NEWLINE
%ignore COMMENT
_NEWLINE: (" "* "\n")+
from lark import Lark
parser = Lark.open("grammar.lark",…
Scriptim
- 1,743
- 2
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- 37
1
vote
0 answers
Python - Lark - Grammar - String
I'm trying to parse a little pseudo-code I'm writing and having some trouble finding which expression format is actually provided as a string.
I was successful to get it working with regex and tokenizer methods, but the strings will be more in…
DonOfDen
- 3,968
- 11
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- 112
1
vote
1 answer
retrieve tokens in lark python
so I'm using the Lark library in python to parse some text and I'm facing 2 problems.
I searched in the documentation but I couldn't find a way to retrieve tokens from a tree, and the second one is that I was expecting a Tree with multiple tokens,…
Djellal Mohamed Aniss
- 1,723
- 11
- 24
1
vote
1 answer
Match substrings in lark
How can properly match substrings using Lark?
My intention (maybe it's not possible/advisable with Lark, or any CFG) is to match and parse only important parts of the string, ignoring the rest. For example:
From "John", I'd like to parse "John" as…
Rodrigo
- 321
- 2
- 11
1
vote
1 answer
Lark: parsing special characters
I'm starting with Lark and got stuck on an issue with parsing special characters.
I have expressions given by a grammar. For example, these are valid expressions: Car{_}, Apple3{3+}, Dog{a_7}, r2d2{A3*}, A{+}... More formally, they have form:…
Matho
- 295
- 5
- 14
1
vote
1 answer
Lark Parser: No terminal defined for ':' (Seeming bias against colon character ":")
I have the following rule (taken from SMTP - RFC5321):
!path : "<" [ a_d_l ":" ] mailbox ">"
When I try to parse this line:
I get the following error:
No terminal defined for ':'
What's unusual is that if I…
Benjamin Basmaci
- 2,247
- 2
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