An Overview of Forth

Forth is a computer programming language invented in 1970 by Charles Moore.
This version of Forth, called WebForth, is designed to teach you how to program in Forth.

Programming Languages

Computers are only useful when they have programs to run on them. Every program must be crafted using a computer programming language.
Because the kinds of problems which people want to solve are so varied, many programming languages have been developed to help do this.
There are several types of programming languages. The main types are: Most languages, including Forth, are procedural languages.

Features of Forth

Forth is a compact language. The main philosophy of Forth is: keep things simple by being flexible. Flexibility is achieved by encouraging the programmer to extend the language until the problem solution is realized as a computer program. The challenge of this approach is that the small details become the concern of the programmer just as much as the large scale is.
Forth gives a unique opportunity for you to understand the underlying hardware of the computer itself. Traditionally Forth gives direct access to all the memory of the computer.

Words

Every procedure in Forth is called a word. Forth knows several hundred words. You create new words using the core set to build your programs. Every word that you build is added to the words already available. The more you use Forth, the more flexible it becomes.

Data Handling

Forth uses a data structure called a stack. The majority of languages use a data stack, but Forth does not hide it from you. The stack is a temporary store for data which are needed by a word. Every word that expects data looks automatically to the top of the stack to find the data it needs. If a word returns data; the data is put onto the stack ready for the next word to use. In consequence, Forth uses fewer variables than the majority of programming languages.

Arithmetic

Another consequence of the direct use of a data stack is post-fix arithmetic. This takes a bit of getting used to but is not difficult. The arithmetic operators are Forth words and need their data just like any other word. To add two numbers together, you make sure they are on the stack before the operator is used. For example: to calculate 8+2 in Forth, you first put the numbers on the stack:
    8 2
You do this merely by typing the numbers and then pressing the [ENTER] key. Then use the operator
    +  
Again, you just type "+" and press [ENTER].
This word adds the two numbers and puts the answer back onto the stack
    10 
which you can see by using the print word, which is the full stop character:
    .  

A side effect of post-fix arithmetic is that brackets to indicate precedence become unnecessary.