Programming Paradigm
Factor is a dynamically typed, functional and object-oriented programming language. Code is structured around small procedures, called words. In typical code, these are 1-3 lines long, and a procedure more than 7 lines long is very rare. Something that would idiomatically be expressed with one procedure in another programming language would be written as several words in Factor.
Each word takes a fixed number of arguments and has a fixed number of return values. Arguments to words are passed on a data stack, using reverse Polish notation. The stack is used just to organize calls to words, and not as a datastructure. The stack in Factor is used in a similar way to the stack in Forth; for this, they are both considered stack languages. For example, below is a snippet of code that prints out "hello world" to the current output stream:
"hello world" printprint is a word in the io vocabulary that takes a string from the stack and returns nothing. It prints the string to the current output stream (by default, the terminal or the graphical listener).
Not all data has to be passed around only with the stack. Lexically scoped local variables let you store and access temporaries used within a procedure. Dynamically scoped variables are used to pass things between procedure calls without using the stack. For example, the current input and output streams are stored in dynamically scoped variables.
Factor emphasizes flexibility and the ability to extend the language. There is a system for macros, as well as for arbitrary extension of Factor syntax. Factor's syntax is often extended to allow for new types of word definitions and new types of literals for data structures. It is also used in the XML library to provide literal syntax for generating XML. For example, the following word takes a string and produces an XML document object which is an HTML document emphasizing the string:
: make-html ( string -- xml ) dupRead more about this topic: Factor (programming Language)
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