CLAC(1)

NAME
clac - A command line, stack-based calculator with postfix notation

SYNOPSIS
clac [expression]

DESCRIPTION
clac is 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 fixed number of arguments, there's no room for ambiguity: parentheses and operator precedence are not needed. Postfix notation is also known as reverse Polish notation, or RPN.

  Non-interactive mode
If an expression is provided, clac will process it and print each element in the stack starting from the top. It will then exit immediately.

  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 subtraction and division invert the order of the arguments before performing 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. A description of the available commands follows.

  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`.

  Logarithm

ln  Pop the value `a` and push its natural logarithm.

log Pop the value `a` and push its logarithm to base 10.

  Factorial

!   Pop the value `a` and push its factorial.

  Trigonometry

sin Pop the value `a` and push its sine.

cos Pop the value `a` and push its cosine.

tan Pop the value `a` and push its tangent.

asin
    Pop the value `a` and push its arc sine.

acos
    Pop the value `a` and push its arc cosine.

atan
    Pop the value `a` and push its arc tangent.

atan2
    Pop two values `a` and `b` and push the arc tangent of `b / a`, using the signs of `a` and `b` to determine the quadrant.

  Error function

erf Pop the value `a` and push its error function.

  Summation

sum Pop all the values in the stack and push their sum.

add Pop the value `a` and remove that many items from the stack. Push their sum.

  Product

prod
    Pop all the values in the stack and push their product.

mul Pop the value `a` and remove that many items from the stack. Push their product.

  Rounding

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

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

round
    Pop the value `a` and push the integer value closest to `a`.

  Absolute value

abs Pop the value `a` and push the non-negative value of `a`.

  Binary operations

and Pop two values `a` and `b` and push the binary AND of `a` and `b`.

or  Pop two values `a` and `b` and push the binary OR of `a` and `b`.

xor Pop two values `a` and `b` and push the binary XOR of `a` and `b`.

  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`.

roll
    Pop two values `a` and `b` and rotate `b` elements in the stack `a` times.

drop
    Remove the top of the stack.

clear
    Remove all the elements in the stack.

count
    Push the number of items in the stack.

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

  Stashing

stash
    Pop the value `a` and move that many items to the stash.

fetch
    Pop the value `a` and move that many items from the stash.

.   Stash the top of the stack.

,   Fetch one stashed item.

:   Stash all the items in the stack.

;   Fetch all stashed items.

  History
Use <C-p> / <C-n> or <Up> / <Down> to navigate the history.

  User defined operations
It is possible to define operations (or words, as they are usually called in stack based programming languages) by editing the words configuration file. It is not created by default, but clac will use some environment variables in order to search for word definitions.

$CLAC_WORDS
    If set, it should point to a file containing word definitions.

$XDG_CONFIG_HOME
    If set, clac will search for $XDG_CONFIG_HOME/clac/words

$HOME
    If set, clac will search for $HOME/.config/clac/words

  How to define words
Words are defined as aliases, with one alias on each line. Empty lines are ignored. Here are some examples:

    pi 3.14159265358979323846
    tau "pi 2 *"
    sqrt "0.5 ^"

Note that an alias has two parts: a word to be defined and its meaning. That's why the tau and sqrt definitions are enclosed in double quotes. If the double quotes are removed, clac will complain that it can't parse the command. For example, if we remove the double quotes from sqrt and start clac, we will get this error message:

    Incorrect definition: sqrt 0.5 ^
    (~/.config/clac/words:3)

User defined words can be used as if they were built-in commands:

    $ clac "42 dup * pi *"
    5541.76944093239

  Comments
Any lines that begin with # are considered comments and are ignored. There are no inline comments, and any # characters that are not the first character of a line are interpreted literally. To define # as a word, wrap it in double quotes in the definition:

    # This is a comment.
    "#" count

The first line is ignored, and the second line assigns # to the operation count.

  How to list defined words
If you type `words` and hit enter, clac will list the defined words.

  How to reload defined words
If you type `reload` and hit enter, clac will reload the words file.

EXAMPLES
While the most interesting aspect of clac is the ability to visualize the stack as it is updated with each key press, at some point you may want use clac just to get a quick result or call it from a script. For that reason, clac can be used in non-interactive mode by invoking it with an argument.

Here are some examples of non-interactive invocations:

    $ clac "3 4 +"
    7

    $ clac "2 3 4 +"
    7
    2

When clac finishes evaluating the expression "2 3 4 +", there are two elements in the stack: the number 7 at the top of the stack and the number 2 at the bottom of the stack. The elements are printed in order, one per line, starting from the top of the stack.

This other example uses the stashing features. Let's say we want to push two numbers and get the result of their multiplication plus the square of the second number.

    $ clac "4 3 dup dup * . * , +"
    21

Another example that uses the stash would be to get the average of all the elements in the stack:

    $ clac "1 2 3 4 count . sum , /"
    2.5

In fact, if you find yourself calculating averages very often, you can define the word avg as "count . sum , /".

AUTHOR
Michel Martens <mail@soveran.com>