UnoScript

UnoScript is a general-purpose, stack-based programming language inspired by the UNO card game. It aims to maximize usability while meeting the constraint that every sequence of UNO cards is a valid program in the language.

This repository holds:

The language specification
An interpreter which implements the specification
A few example programs
A formal specification written in TLA+

Building the Interpreter

The interpreter is written in C++, with dependencies on flex, gcc, and make.

To build the interpreter, open a terminal, cd into the project directory and run make. The Makefile expects that the executables flex and g++ are available on your terminal's PATH.

This will compile the interpreter source and create an executable named uno.

Running Programs

UnoScript programs can be run by passing them as input to the uno executable. By convention, UnoScript programs use the file extension ".uno".

For example, to run the hello world program, run this from the project root:

./uno < examples/hello_world.uno

Verbose Mode

To aid in writing UnoScript programs the interpreter provides a verbose mode.

In verbose mode, as each instruction is processed, the interpreter prints out:

The program source, with an arrow indicating the position of the head
The top five items on the stack

To enable this, pass the -v or --verbose flag to the interpreter, for example:

./uno --verbose < examples/hello_world.uno

Interpreting verbose output

For example, the output below shows an addition operation.

In the first state, a draw2 card is at the top of the stack with the head over a r0 card. The head reads the r0 card, pops the draw2 off the stack, and operates on the top two items on the stack.

r0 corresponds to addition, so the top of the stack is replaced with g0 + b1 = b1. The head moves to the next card.

-------------------------------
|r1   |b1   |draw2|r0   |draw2| (Tape)
-------------------------------
  55    56    57  ^ 58    59
-------------------------------
|y101 |b12  |g0   |b1   |draw2| (Stack)
-------------------------------

-------------------------------
|r1   |b1   |draw2|r0   |draw2| (Tape)
-------------------------------
  55    56    57    58  ^ 59
-------------------------------
|y108 |r108 |y101 |b12  |b1   | (Stack)
-------------------------------

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