pegjs | PEG.js : Parser generator for JavaScript | Parser library
kandi X-RAY | pegjs Summary
kandi X-RAY | pegjs Summary
PEG.js is a simple parser generator for JavaScript that produces fast parsers with excellent error reporting. You can use it to process complex data or computer languages and build transformers, interpreters, compilers and other tools easily. PEG.js is still very much work in progress. There are no compatibility guarantees until version 1.0.
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Top functions reviewed by kandi - BETA
- Parses the root of the peg .
- Generates JS code from an AST .
- Generate byte code from AST
- Parses the open code .
- Inner implementation of AST evaluation
- Generate the template tables
- Parse a single character .
- Parse a multi - line comment .
- Parse a multi - line comment .
- Parse single line
pegjs Key Features
pegjs Examples and Code Snippets
Community Discussions
Trending Discussions on pegjs
QUESTION
In "Packrat Parsing: a Practical Linear-Time Algorithm with Backtracking" on page 30 the author states that the context-free grammar (CFG):
...ANSWER
Answered 2022-Jan-11 at 23:02You just didn't test enough. Try inputs consisting of an odd number of a
s. All match the grammar but PEG only accepts those of length 2k−1 for some integer k.
QUESTION
I am very beginner to PEGjs I need help to implement variable (identifier) declaration support to my parser.
My input code look like:
...ANSWER
Answered 2021-Oct-22 at 12:14try this:
QUESTION
I want to handle string starts with number
using pegjs. When I input with 1abcd it throws Expected [0-9.] or end of input but "a" found.
. The expected output is { item: '1abcd', case: '=' }
. What changes do I need?
ANSWER
Answered 2021-Oct-18 at 15:19Since NUMBER
matches the first character, you'll want to use a negative lookahead for STRING
before returning a successful match. That way, if a STRING
character is encountered, the NUMBER
rule will fail and the second alternation of start
will be used.
Here's an example, although as @thinkgruen has written, you'll probably want to try to parse floats less loosely as well.
QUESTION
I have written the code to parse the following expression
...ANSWER
Answered 2021-Aug-16 at 09:22Do not use string functions to parse comparison operators, make them a part of your grammar. For chained operations like 'AND' use a rule like this:
QUESTION
I have written the code to parse the following expression
...ANSWER
Answered 2021-Aug-13 at 09:15I guess you can describe your language with the following grammar:
QUESTION
There is a text:
...ANSWER
Answered 2021-Jun-21 at 11:32Your Literal
rule accepts quoted strings, what you can do is when you are parsing id, you match everything until you find a }
, when you parse type you match everything until you see a ]
, when you parse description you match everything until you see )
, and when parsing the title you match everything until you see a .
then your rule Element
will produce the result you want.
QUESTION
I have this lexeme:
...ANSWER
Answered 2021-May-24 at 14:49*
matches zero or more repetitions of its operand, as you say.
So when you write
QUESTION
I have created a Vue.js library and included it in a Nuxt.js project. The problem is that I'm seeing duplicate Vue.js instances being created from both the Nuxt instance and the library, whereas the library should use the Vue instance from Nuxt.js:
You can see it's being printed twice from two different instances.
How can I make sure that only one instance is used? This is causing all sorts of issues.
Things I have already done:
- The webpack configuration of the library has
'vue'
as an external dependency. (How is it possible that even though it is marked as external in the library the library still dynamically imports it?) 'vue'
is apeerDependency
in thepackage.json
file of the library.
Additional information:
- The library is included in the Nuxt project using
npm link
- This eventually causes errors of the sort of
$attrs is readonly.
errors and such. - This only happens in development, production builds seem to be working fine. No errors.
- The first instance is from
webpack:///./node_modules/vue/dist/vue.runtime.esm.js?2b0e
(Nuxt.js presumably) - The second instance is from
webpack-internal:///../minerva/node_modules/vue/dist/vue.runtime.esm.js
(the library)
The library exports this component and has this webpack configuration:
...ANSWER
Answered 2021-Apr-21 at 05:43As I said in the comments, You should use a Plugin
for importing your library.
For example, I have a file named my-custom-plugin.js:
QUESTION
As part of my parser I want to add arithmetic and boolean expressions. I wanted to take default PEG.js example at https://pegjs.org/online but the problem is that that parser is recursive and you can't write two or more lines:
For instance this is valid JavaScript:
...ANSWER
Answered 2021-Mar-26 at 14:59You could add a Start
rule like the following for multiple expressions.
QUESTION
I'm working on a Peg parser. Among other structures, it needs to parse a tag directive. A tag can contain any character. If you want the tag to include a curly brace }
you can escape it with a backslash. If you need a literal backslash, that should also be escaped. I tried to implement this inspired by the Peg grammer for JSON: https://github.com/pegjs/pegjs/blob/master/examples/json.pegjs
There are two problems:
- an escaped backslash results in two backslash characters instead of one. Example input:
ANSWER
Answered 2021-Mar-21 at 16:42These errors are both basically typos.
The first problem is the character class in your regular expression for tag characters. In a character class, \
continues to be an escape character, so [^\}\r\n]
matches any character other than }
(written with an unnecessary backslash escape), carriage return or newline. \
is such a character, so it's matched by the character class, and Escape
is never tried.
Since your pattern for tag characters doesn't succeed in recognising \
as an Escape
, the tag { \\ }
is parsed as four characters (space, backslash, backslash, space) and the tag { \} }
is parsed as terminating on the first }
, creating a syntax error.
So you should fix the character class to [^}\\\r\n]
(I put the closing brace first in order to make it easier to read the falling timber. The order is irrelevant.)
Once you do that, you'll find that the parser still returns the string with the backslashes intact. That's because of the $
in your Tag
pattern: "{" _ tagContent:$(TagChar+) _ "}"
. According to the documentation, the meaning of the $
operator is: (emphasis added)
$ expression
Try to match the expression. If the match succeeds, return the matched text instead of the match result.
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