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.
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.
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
.
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:
+
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
.
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.
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.
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.