JSON Parser

A Python-based JSON parser and scanner that reads tokenized input from .txt files, builds a parse tree, and outputs valid JSON or a structured error message.

🧠 Features

• Custom scanner to tokenize JSON-like inputs
• Recursive descent parser
• Handles objects, arrays, strings, numbers, booleans, and nulls
• Type validation for arrays (homogeneous elements)
• Detects and reports:
  • Invalid tokens
  • Duplicate keys in objects
  • Type mismatches in arrays
  • Malformed numbers and strings
  • Extra trailing commas
• Outputs valid .json files or JSON-formatted error messages

📁 Project Structure

• json_scanner.py | Defines TokenType, Token, and Lexer classes
• json_parser.py | Main parser logic
• test0X.txt | Example input files
• output0X.json | Output files (created after running)

🧪 Input Format

Input .txt files contain pre-tokenized lines. Examples:

<{> 
<str,"name"> 
<:> 
<str,"Ben"> 
<,> 
<str,"age"> 
<:> 
<num,21> 
<}>

🧾 Output Format

On success:

{
  "name": "Ben",
  "age": 21
}

On error:

{
  "error": "Error type 5 at \"name\": Duplicate keys found."
}

🚀 Getting Started

0. Ensure you have python3 installed.
1. Clone the repo

git clone https://github.com/your-username/json-parser.git
cd json-parser

2. Adjust test files to your liking in test.00.txt, test.01.txt, etc.

3. Run the parser

python3 json_parser.py

⚠️ Error Types

Specific Types:

1. Malformed number (starts/ends with a dot)
2. Empty string
3. Number starts with + or leading 0
4. Reserved words used as strings (e.g. "true")
5. Duplicate keys in objects
6. Mixed types in arrays

Other:

• Extra comma Trailing commas in arrays or objects

📃 License

MIT License