json parse CLI example in nim, from https://x.com/lemire/status/1839881289312149549

README.md

SETUP:

Install nim

REPO_PATH=$HOME/repos
cd $REPO_PATH
git clone git@github.com:nim-lang/Nim.git
cd Nim
./build_all.sh

# add to your path - change to bashrc if you use bash
echo "export PATH='${REPO_PATH}/Nim/bin/:\$PATH'" >> ~/.zshrc

Now go to this repo location and run nimble install - nimble is used to install cligen. With cligen, you have CLI parsing based off function argument types - which is great for quick iteration speed. There are alternatives to this library.

Notably, for this example, we could have used commandLineParams() from std/cmdline

BENCHMARK:

The below will compile the nim program & run hyperfine on it for you:

nim benchmarkNim

Result: 3.5 ms ± 4.1 ms

For reference, here is python:

nim benchmarkPy

Result: 32.3 ms ± 4.2 ms

Example benchmarks were run on an M1 Max.

RUN IT YOURSELF:

The below compiles and runs the program on the input

nim c -d:release -r parse_json.nim --inputFile wealth.json

or:

nim compile
nim runExample

see config.nims for tasks

config.nims

--outdir:"build"
--nimcache:"build/cache"

proc compile = 
  echo "compiling ..."
  exec "nim c -d:release parse_json.nim"

task runExample, "run parse_json on the example json":
  exec "./build/parse_json --inputFile ./wealth.json"

task compile, "compile and benchmark nim":
  compile()

task benchmarkNim, "compile and benchmark nim":
  compile()
  exec "hyperfine --runs 1000 --warmup 100 './build/parse_json --inputFile ./wealth.json'"

task benchmarkPy, "compile and benchmark nim":
  exec "hyperfine --runs 1000 'python3 parse_json.py ./wealth.json' --warmup 100"

parse_json.nim

import std/[json, strutils, strformat]
import cligen
    
proc main(inputFile: string) =
  let 
    data = parseFile(inputFile)
    wealthStr = data["user"]["wealth"].getStr
    wealth = wealthStr.parseFloat
  echo &"parse the wealth: {wealth:.2f}"

when isMainModule:
  dispatch main

parse_json.nimble

# Package

version       = "0.1.0"
author        = "Miguel Martin"
description   = "A new awesome nimble package"
license       = "MIT"
srcDir        = "src"


# Dependencies

requires "nim >= 2.0.8"
requires "cligen"

parse_json.py

import json
import sys

file_path = sys.argv[1]

with open(file_path, 'r') as file:
  data = json.load(file)
wealth_str = data['user']['wealth']
wealth = float(wealth_str)
print(f"parsed the wealth {wealth:.2f}")

wealth.json

{
    "user": {
      "name": "John Doe",
      "age": 30,
      "email": "john@cia.gov.us",
      "address": {
        "street": "123 Main St",
        "city": "Springfield",
        "state": "IL",
        "zip": "62701"
      },
      "phone": [
        {
          "type": "home",
          "number": "217-555-5555"
        },
        {
          "type": "work",
          "number": "217-555-5556"
        }
      ],
      "children": [
        {
          "name": "Jane Doe",
          "age": 5
        },
        {
          "name": "Jesse Doe",
          "age": 8
        }
      ],
      "wealth": "12321321321.128888"
    }
  }