mattiadg / calc

A hand-rolled interpreter for a simple calculator

Calc

A basic calculator that supports the 4 base operations and parentheses. It is written as a simple interpreter with hand-written lexer, Pratt parser and Tree Walk interpreter.
No compiler-compiler tools are used, following the spirit of books such as Crafting Interpreters and Writing an Interpreter in Go. The goal is twofold: leave no space for "magic" in the implementation, and learn C++.

Please, note that this is a toy project with educational purpose and not something that will ever go in production anywhere.
It comes with a cmake recipe and a small Google Test suite, having the same goal in mind of familiarizing with such technologies.

Forking this repo to add more features and improve its codebase is strongly encouraged. I am releasing it to share this learning project with anybody that may need it.

Compile

git clone the project and in the main folder run

$ cmake -S . -B build && cmake --build build

the executables will be under the build folder.

Ideas for Improvement

Try the following to make practice with C++ and interpreters:

• Improve error messages (currently only partly implemented in the Lexer)
• Use ans to refer to the latest expression result
• Add built/in functions, for instance trigonometric functions
• Add possibility of user-defined functions
• Add vector or matrix arythmetic

The more functionalities added and the more the resulting language looks like an actual programming language.

Example

$ ./calc "(2 + 3) * 7"
 35

License

This project has to be considered "public domain" and is released with double license MIT and Apache. Reuse it with the license you find more appropriate.