Stacky - a stack based programming language inspired by forth

Implemented

• Built-in functions: DUB, SWAP, DROP, PUTS
• Words
• If-Else-Then
• Do-Loops
• Variables

Explanation

Basic functions

• DUB : duplicates the last item on the stack
• SWAP : swaps the last two items on the stack
• DROP : drops the last item on the stack
• PUTS : takes a length n from the stack and the next n elements and prints them
• EMIT (.) : takes and prints the last item on the stack

Word

A word defines a list of expressions that will be executed if the word is called. The basic syntax for a word is:

: [IDENTIFIER] [EXPRESSIONS] ;

Example:

: Add + ;
1 2 Add . 

will output 3

IF

The basic syntax for an if-statement is:

[CONDITION] IF [EXPRESSIONS] ELSE [EXPRESSIONS] THEN

The IF-Expression pops the last item from the stack and checks the condition. If the condition is met the if if-expressions-block is executed. Elsewise the else-expressions-block is executed.

A simple condition is: 1 1 = which evaluates to 1 (true).

LOOP

The basic syntax of a do-loop-expression is:

[LIMIT] [INDEX] DO [EXPRESSIONS] LOOP

The limit and the index get popped from the stack and are pushed to the loop-stack. Every loop-iteration the limit and the index get popped from the loop-stack to check if the looping condition (index < limit) is valid. After the loop-iteration the limit and the updated index are pushed back to the loop-stack.

Variables

Variables can hold data.

To assign data to a variable use the -> operator:

1 -> X

The number 1 is assigned to X. This operation will pop the 1 from the stack.

To get the data from an variable use the @ operator:

@ X

This puts the data in X on the stack.

For now variables are global so this:

: Test @ X . ;
2 -> X
Test

will print 2