Forth (programming language)

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Forth is a stack-based programming language and interactive programming environment designed by Charles H. Moore in the late 1960s. It is known for its simplicity, extensibility, and efficiency, making it popular in embedded systems, real-time applications, and resource-constrained environments.

History

Forth was developed by Charles H. Moore while working at the National Radio Astronomy Observatory (NRAO). The language was first implemented in 1970 and was used to control radio telescopes. The name "Forth" was chosen because the original IBM 1130 system had a five-character limit for file names, and "Fourth" (as in "fourth-generation language") was shortened to "Forth."

Design and Features

Forth is characterized by its use of a stack for parameter passing and its concatenative programming style. The language operates in an interactive mode, allowing programmers to define new words (functions) and test them immediately.

Key Features

• **Stack-based**: Forth uses a stack to hold data and return addresses, which simplifies the language's syntax and implementation.
• **Extensible**: Users can define new words and extend the language's vocabulary.
• **Interactive**: Forth provides an interactive environment where code can be tested and executed immediately.
• **Minimalistic**: The language has a small set of core words, making it easy to learn and implement.

Syntax and Semantics

Forth's syntax is minimalistic and consists of words separated by spaces. Words are either built-in commands or user-defined functions. The language uses Reverse Polish Notation (RPN) for arithmetic operations, which means operators follow their operands.

Example

A simple Forth program to add two numbers and print the result: ```

ADD-TWO ( n1 n2 -- n3 )

+ . ;

``` In this example, `: ADD-TWO` defines a new word that takes two numbers from the stack, adds them, and prints the result.

Applications

Forth is widely used in embedded systems, real-time applications, and systems programming. Its efficiency and low resource requirements make it suitable for microcontrollers and other resource-constrained environments.

Implementations

There are several implementations of Forth, including:

• GForth
• SwiftForth
• SP-Forth
• ColorForth

Related Concepts

• Stack machine
• Concatenative programming language
• Reverse Polish Notation
• Embedded system

See Also

• Charles H. Moore
• Programming language
• Interactive programming environment
• Real-time computing