Forth (programming language): Difference between revisions

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Forth emphasizes the use of small, simple functions called ''words''. Words for bigger tasks call upon many smaller words that each accomplish a distinct sub-task. A large Forth program is a hierarchy of words. These words, being distinct modules that communicate implicitly via a stack mechanism, can be prototyped, built and tested independently. The highest level of Forth code may resemble an English-language description of the application. Forth has been called a ''meta-application language'': a language that can be used to create [[Domain-specific language|problem-oriented languages]].<ref>{{cite book |last=Brodie |first=Leo |title=Starting Forth |edition=2nd |year=1987 |publisher=Prentice-Hall |isbn=978-0-13-843079-5 |url=https://www.forth.com/starting-forth/index.html}}</ref>

Forth relies on implicit use of a [[stack (abstract data structuretype)|data stack]] and [[reverse Polish notation]] which is commonly used in calculators from [[Hewlett-Packard]]. In RPN, the operator is placed after its operands, as opposed to the more common [[infix notation]] where the operator is placed between its operands. Postfix notation makes the language easier to parse and extend; Forth's flexibility makes a static [[Backus-Naur form|BNF]] grammar inappropriate, and it does not have a monolithic compiler. Extending the compiler only requires writing a new word, instead of modifying a grammar and changing the underlying implementation.

Using RPN, one can get the result of the mathematical expression <code>(25 * 10 + 50)</code> this way: