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Challenge 34 - Write Your Own jq

This is the challenge 34 from the Coding Challenges by John Crickett https://codingchallenges.fyi/challenges/challenge-jq

Description

This solution implements a jq (json query) evaluator

  • its based on my own made jquery parser and object model from challenge-no https://github.com/lolo8304/coding-challenge/tree/main/no-2

  • a new lexer + parser again for the jq language

  • build a simple node tree to use for recursive evaluation of jq expressions

  • implement own classes per expression type

  • built a new JsonSerializer with compact, indentations etc in it, to be able to pretty-print the json

Final result

the final array builder uses all features (. | [] selectors)

curl -s 'https://api.github.com/repos/CodingChallegesFYI/SharedSolutions/commits?per_page=3' | ./jq.sh "[.[].[\"commit\"].author | { name, email }] "
[
    {
        "name": "Lorenz aka Lolo Hänggi",
        "email": "[email protected]"
    },
    {
        "name": "Ethan Costa",
        "email": "[email protected]"
    },
    {
        "name": "Carlos Gómez",
        "email": "[email protected]"
    }
]

There is a very good documention about the language features. https://jqlang.github.io/jq/manual/ Could be lots of additional challenges to be solved :-)

Build

Open Intellij or any other IDE with gradle support. run "installDist"

Tests

Run test cases using gradle "test" command. checkout many test files for bit converter, qr code, qr mode, regions, version

Usage

Commandline parameters

I am using picocli to parse arguments

./jq.sh -h
Usage: jq [-hvV] [-vv] [<jqFilter>] [<files>...]
This challenge is to build your own jq - see https://codingchallenges.
fyi/challenges/challenge-jq
      [<jqFilter>]   jq filter expressions - default '.'
      [<files>...]   files - optional
  -h, --help         Show this help message and exit.
  -v                 -v specifies verbose level
  -V, --version      Print version information and exit.
      -vv            -vv specifies verbose level 2

remark: the coding was quite simple, there is was no need for -v or -vv

Examples:

get all quotes of objects. checkout the real json answer via https://dummyjson.com/quotes?limit=2

curl -s 'https://dummyjson.com/quotes?limit=2' | ./jq.sh '.["quotes"]'
[
    {
        "id": 1,
        "quote": "Life isn’t about getting and having, it’s about giving and being.",
        "author": "Kevin Kruse"
    },
    {
        "id": 2,
        "quote": "Whatever the mind of man can conceive and believe, it can achieve.",
        "author": "Napoleon Hill"
    }
]

search for the first element, and the the commit message

curl -s 'https://api.github.com/repos/CodingChallegesFYI/SharedSolutions/commits?per_page=3' | ./jq.sh '.[0] | .commit.message'
"Added QR code generator  (#72)\n\n* Create challenge-qr-generator.md\r\n\r\n* Update README.md with QR code generator"

Debugging:

  • I prepared -v and -vv, but I did not use it

TODO / Bugs

  • some of the code in the evaluator could be refactored heavily
  • push back the json parser code to the example no-2 code

Final note

I did not know "jq" before this challenge. It shows that John's challenges are always good to learn coding something new and also get to know something new.