Compose Language Introduction

About Compose

Compose is my concatenative language, designed for writing concise functions and programs in a tacit style. Functions are made up of data terms and function applications.

Data terms

When data terms are encountered, such as 10 or false or ( copy * ), they are pushed to the virtual machine's stack. The most recently pushed data will be consumed first by applied functions.

Functions

Core Functions

Compose provides a number of core functions that can be evaluated such as arithmetic operations, Boolean logic operations, and stack operations such as copy, drop, swap and others. Along with data terms, these are the main building blocks of any other function or program.

Named Functions

Named functions can be defined by writing their identifiers, and then their function bodies (delimited by a : and a ;). Recursion is supported as shown in the factorial example below.

Examples

Cubing a Number: cube : copy copy * * ;

2 cube → 8

5 cube → 125

Fibonacci Sequence: fibonacci : hop hop + ;

5 10 fibonacci → 5 10 15

1 2 fibonacci fibonacci fibonacci → 1 2 3 5 8

Factorials: factorial : copy = 1 ( ) ( copy 1 - factorial * ) ? ;

5 factorial → 120

20 factorial → 2432902008176640000

Lambdas

Lambdas are data terms that represent functions stored on the stack as arguments for other functions. They are written as a function body delimited by parentheses. A lambda on top of the stack can be popped from the stack and evaluated with the apply function as shown below.

8 ( copy * ) apply → 64

Lambdas can be composed into new lambdas using the compose function. Lambdas are composed simply by concatenating their function bodies. A lambda that adds 5 to a number and a lambda that doubles a number can be combined into one lambda that adds 5 to and then doubles a number.

( 5 + ) ( 2 * ) → ( 5 + 2 * )

Try Compose

You can download and try Compose using Cargo.

cargo install compositor

The interactive environment can be started with the command cmpstr.