A Quick Tutorial

Programming in RETRO is all about creating words to solve the problem at hand. Words operate on data, which can be kept in memory or on the stack.

Let's look at this by solving a small problem: writing a word to determine if a string is a palindrome.

A palindrome is a phrase which reads the same backward and forward.

We first need a string to look at. Starting with something easy:

```
'anna
```

Looking in the Glossary, there is a s:reverse word for reversing a string. We can find dup to copy a value, and s:eq? to compare two strings. So testing:

```
'anna dup s:reverse s:eq?
```

This yields -1 (TRUE) as expected. So we can easily name it:

```
:palindrome? dup s:reverse s:eq? ;
```

Naming uses the : prefix to add a new word to the dictionary. The words that make up the definition are then placed, with a final word (;) ending the definition. We can then use this:

```
'anna palindrome?
```

Once defined there is no difference between our new word and any of the words already provided by the RETRO system.