Clac

A command line, stack-based calculator with postfix notation that displays the stack contents at all times. As you type, the stack changes are reflected immediately.

In a stack-based postfix calculator, entering a number pushes it on a stack, and arithmetic operations pop their arguments from the stack and push the result. As all the operations take a fix number of arguments, there's no room for ambiguity: parenthesis and operator precedence are not needed. Postfix notation is also known as reverse Polish notation, or RPN.

Why?

I like Forth and other stack based, concatenative languages, and I've used the dc calculator a lot. Once I got used to dc, other calculators seemed to be less powerful. While it has been extremely useful for me, I've always found the UI a bit lacking. That's why I decided to try this idea of an always-visible stack with realtime updates.

Installation

Install clac into /usr/local/bin with the following command:

$ make install

You can use make PREFIX=/some/other/directory install if you wish to use a different destination. If you want to remove clac from your system, use make uninstall.

Commands

When a command requires an argument, it pops a value from the stack. If the stack is empty, a zero is provided instead. In the descriptions below, the top of the stack (and thus the first value popped) is represented by the letter a, while the second value popped is represented by the letter b. For example, if the stack is composed of the number 1, 2 and 3 (with 3 at the top of the stack), when we describe the sum then a will be 3 and b will be 2. It is important to note that substraction and division invert the order of the arguments before peforming the operation: with 1, 2 and 3 in the stack, when you type - it will pop the values 3 and 2 and push the result of 2 - 3. This is in the tradition of other postfix calculators and programming languages.

Here's a description of the available commands:

Arithmetic operations

+ Pop two values a and b and push the result of a + b.

- Pop two values a and b and push the result of b - a.

* Pop two values a and b and push the result of a * b.

/ Pop two values a and b and push the result of b / a.

Modulo operation

% Pop two values a and b and push the remainder of the Euclidean division of b by a.

Exponentiation

^ Pop two values a and b and push the result of b ^ a.

Rounding

ceil Pop the value a and push smallest integral value greater than or equal to a.

floor Pop the value a and push largest integral value less than or equal to a.

round Pop the value a and push integral value nearest to a.

Stack manipulation

swap Pop two values a and b and push the values a, b.

dup Pop the value a and push the values a, a.

_ Push on the stack the result of the last operation.

What is missing

It is likely that more operations will be added in the future. I didn't add every possible stack manipulation command because I'm trying to let usage define the API, and the fact that the calculator has line editing capabilities makes some commands less useful. For example, drop is trivial to implement (two lines of code), yet I didn't include it in the API because I haven't had the need to use it so far. I like to keep the code short, that's why I didn't go ahead implementing commands just in case. That said, let me know if you find use cases for other commands (or even for drop!) and we will either find a better solution or we'll end up implementing them.

Contributing

If you find a bug, please create an issue detailing the ways to reproduce it. If you have a suggestion, create an issue detailing the use case.