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content-type: "page"
title: "Learn"
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{@ _defs_.md || 0 @}

{{m}} is a stack-based, concatenative programming language that uses postfix notation. If you already know [Forth](http://www.forth.org/), [Factor](http://factorcode.org/) or [Joy](http://www.kevinalbrecht.com/code/joy-mirror/), or if you ever used an [RPN](https://en.wikipedia.org/wiki/Reverse_Polish_notation) calculator, then {{m}} will look somewhat familiar to you. 

If not, well, here's how a short {{m}} program looks like:

    ; This is a comment
    (1 2 3 4 5) (dup *) map
    #| This is a...
       ...multiline comment |#

This program returns a list containing the square values of the first five integer numbers:

    (1 4 9 16 25)

Let's see how it works:

1. First, a list containing the first five integers is pushed on the stack.
2. Then, another list containing two symbols (`dup` and `*`) is pushed on the stack. This constitutes a quoted program which, when executed duplicates the first element on the stack — this is done by `dup`— and then multiplies — with `*`— the two elements together.
3. Finally, the symbol `map` is pushed on the stack. Map takes a list of elements and a quoted program and applies the program to each element.

Note that:

* There are no variable assignments.
* elements are pushed on the stack one by one.
* Parentheses are used to group one or more elements together so that they are treated as a single element and they are not evaluated immediately.
* *Symbols* (typically single words, or several words joined by dashes) are used to execute code that performs operations on the whole stack.

Unlike more traditional programming languages, in a concatenative programming language, there is no inherent need for variables or named parameters, as symbols act as stack symbols that consume elements that are placed in order on top of a stack.