What is forth?

Forth is a simple, stack‑based programming language created in the 1970s. It lets you write programs by defining short words (functions) that manipulate a data stack, using a very minimal syntax. Because the language is interactive and extensible, you can add new words while the program runs.

Let's break it down

  • Stack: Think of a pile of plates. You can only add (push) or remove (pop) the top plate. Forth stores numbers and data on this stack.
  • Words: The building blocks of Forth code. Each word is like a command that takes items from the stack, does something, and puts results back.
  • Dictionary: A list where all defined words are stored. You can add your own words, effectively extending the language.
  • Reverse Polish Notation (RPN): Operations are written after their operands (e.g., 3 4 + instead of 3 + 4). This matches how the stack works.
  • Interpreter/Compiler: Forth runs interactively (you type a word, it executes) but can also compile words into fast machine code.

Why does it matter?

Forth’s design gives programmers direct control over hardware with very little overhead, making it great for low‑level tasks. Its interactive nature speeds up prototyping, and because you can extend the language itself, it adapts to many specialized problems. Understanding Forth also teaches fundamental concepts like stacks and postfix notation, which appear in calculators and other languages.

Where is it used?

  • Embedded systems (e.g., spacecraft, medical devices, industrial controllers)
  • Real‑time operating systems and bootloaders
  • Some audio and music equipment (synthesizers, effects processors)
  • Educational tools for teaching low‑level programming concepts
  • Niche hobbyist projects and retro computing communities

Good things about it

  • Extremely small footprint - runs on very limited memory and CPU resources
  • Fast execution because many words compile to native code
  • Highly extensible; you can create domain‑specific vocabularies
  • Interactive development loop speeds up testing and debugging
  • Simple core language makes the compiler itself easy to understand and port

Not-so-good things

  • Unconventional syntax (RPN) can be hard for beginners to read
  • Limited standard libraries compared to modern languages
  • Sparse community and fewer learning resources today
  • Debugging can be tricky without modern IDE support
  • Not ideal for large, complex applications where structured, object‑oriented designs are preferred.