Factor (programming language)
Encyclopedia
Factor is a stack-oriented
programming language
created by Slava Pestov. Factor is dynamically typed and has automatic memory management, as well as powerful metaprogramming features. The language has a single implementation featuring a self-hosted optimizing compiler
and an interactive development environment
. The Factor distribution includes a large standard library
.
for a video game. The initial implementation, now referred to as JFactor, was implemented in Java
and ran on the Java Virtual Machine
. Though the early language resembled modern Factor superficially in terms of syntax, the modern language is very different in practical terms and the current implementation is much faster.
The language has changed significantly over time. Originally, Factor programs centered around manipulating Java objects with Java's reflection
capabilities. From the beginning, the design philosophy has been to modify the language to suit programs written in it. As the Factor implementation and standard libraries grew more detailed, the need for certain language features became clear, and they were added. JFactor did not have an object system where you could define your own class
es, and early versions of native Factor were the same; the language was similar to Scheme in this way. Today, the object system is a central part of Factor. Other important language features such as tuple
classes, combinator inlining, macros, user-defined parsing
words and the modern vocabulary system were only added in a piecemeal fashion as their utility became clear.
The foreign function interface
was present from very early versions to Factor, and an analogous system existed in JFactor. This was chosen over creating a plugin to the C
part of the implementation for each external library that Factor should communicate with, and has the benefit of being more declarative
, faster to compile and easier to write.
The Java implementation initially consisted of just an interpreter
, but a compiler to Java bytecode
was later added. This compiler only worked on certain procedures. The Java version of Factor was replaced by a version written in C and Factor. Initially, this consisted of just an interpreter, but the interpreter was replaced by two compilers, used in different situations. Over time, the Factor implementation has grown significantly faster.
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" print
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 )
dup
<->
<body><h1><-></h1></body>
XML> ;
The word
A foreign function interface
is built in to Factor, allowing for communication with C
, Objective-C
and Fortran
programs. There is also support for executing and communicating with shaders written in GLSL
.
Factor is implemented in Factor and C++
. It was originally bootstrapped from an earlier Java implementation. Today, the parser and the optimizing compiler are written in the language. Certain basic parts of the language are implemented in C++ such as the garbage collector and certain primitives.
Factor uses an image
-based model, analogous to many Smalltalk
implementations, where compiled code and data are stored in an image. To compile a program, the program is loaded into an image and the image is saved. A special tool assists in the process of creating a minimal image to run a particular program, packaging the result into something that can be deployed as a standalone application.
The Factor compiler implements many advanced optimizations and has been used as a target for research in new optimization techniques.
Stack-oriented programming language
A stack-oriented programming language is one that relies on a stack machine model for passing parameters. Several programming languages fit this description, notably Forth, RPL, PostScript, and also many Assembly languages ....
programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
created by Slava Pestov. Factor is dynamically typed and has automatic memory management, as well as powerful metaprogramming features. The language has a single implementation featuring a self-hosted optimizing compiler
Compiler optimization
Compiler optimization is the process of tuning the output of a compiler to minimize or maximize some attributes of an executable computer program. The most common requirement is to minimize the time taken to execute a program; a less common one is to minimize the amount of memory occupied...
and an interactive development environment
Integrated development environment
An integrated development environment is a software application that provides comprehensive facilities to computer programmers for software development...
. The Factor distribution includes a large standard library
Standard library
A standard library for a programming language is the library that is conventionally made available in every implementation of that language. In some cases, the library is described directly in the programming language specification; in other cases, the contents of the standard library are...
.
History
Slava Pestov created Factor in 2003 as a scripting languageScripting language
A scripting language, script language, or extension language is a programming language that allows control of one or more applications. "Scripts" are distinct from the core code of the application, as they are usually written in a different language and are often created or at least modified by the...
for a video game. The initial implementation, now referred to as JFactor, was implemented in Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
and ran on the Java Virtual Machine
Java Virtual Machine
A Java virtual machine is a virtual machine capable of executing Java bytecode. It is the code execution component of the Java software platform. Sun Microsystems stated that there are over 4.5 billion JVM-enabled devices.-Overview:...
. Though the early language resembled modern Factor superficially in terms of syntax, the modern language is very different in practical terms and the current implementation is much faster.
The language has changed significantly over time. Originally, Factor programs centered around manipulating Java objects with Java's reflection
Reflection (computer science)
In computer science, reflection is the process by which a computer program can observe and modify its own structure and behavior at runtime....
capabilities. From the beginning, the design philosophy has been to modify the language to suit programs written in it. As the Factor implementation and standard libraries grew more detailed, the need for certain language features became clear, and they were added. JFactor did not have an object system where you could define your own class
Class (computer science)
In object-oriented programming, a class is a construct that is used as a blueprint to create instances of itself – referred to as class instances, class objects, instance objects or simply objects. A class defines constituent members which enable these class instances to have state and behavior...
es, and early versions of native Factor were the same; the language was similar to Scheme in this way. Today, the object system is a central part of Factor. Other important language features such as tuple
Tuple
In mathematics and computer science, a tuple is an ordered list of elements. In set theory, an n-tuple is a sequence of n elements, where n is a positive integer. There is also one 0-tuple, an empty sequence. An n-tuple is defined inductively using the construction of an ordered pair...
classes, combinator inlining, macros, user-defined parsing
Parsing
In computer science and linguistics, parsing, or, more formally, syntactic analysis, is the process of analyzing a text, made of a sequence of tokens , to determine its grammatical structure with respect to a given formal grammar...
words and the modern vocabulary system were only added in a piecemeal fashion as their utility became clear.
The foreign function interface
Foreign function interface
A foreign function interface is a mechanism by which a program written in one programming language can call routines or make use of services written in another. The term comes from the specification for Common Lisp, which explicitly refers to the language features for inter-language calls as...
was present from very early versions to Factor, and an analogous system existed in JFactor. This was chosen over creating a plugin to the C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
part of the implementation for each external library that Factor should communicate with, and has the benefit of being more declarative
Declarative programming
In computer science, declarative programming is a programming paradigm that expresses the logic of a computation without describing its control flow. Many languages applying this style attempt to minimize or eliminate side effects by describing what the program should accomplish, rather than...
, faster to compile and easier to write.
The Java implementation initially consisted of just an interpreter
Interpreter (computing)
In computer science, an interpreter normally means a computer program that executes, i.e. performs, instructions written in a programming language...
, but a compiler to Java bytecode
Java bytecode
Java bytecode is the form of instructions that the Java virtual machine executes. Each bytecode opcode is one byte in length, although some require parameters, resulting in some multi-byte instructions. Not all of the possible 256 opcodes are used. 51 are reserved for future use...
was later added. This compiler only worked on certain procedures. The Java version of Factor was replaced by a version written in C and Factor. Initially, this consisted of just an interpreter, but the interpreter was replaced by two compilers, used in different situations. Over time, the Factor implementation has grown significantly faster.
Programming paradigm
Factor is a dynamically typed, functionalFunctional programming
In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes the application of functions, in contrast to the imperative programming style, which emphasizes changes in state...
and object-oriented
Object-oriented programming
Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
. 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
Stack (data structure)
In computer science, a stack is a last in, first out abstract data type and linear data structure. A stack can have any abstract data type as an element, but is characterized by only three fundamental operations: push, pop and stack top. The push operation adds a new item to the top of the stack,...
, using reverse Polish notation
Reverse Polish notation
Reverse Polish notation is a mathematical notation wherein every operator follows all of its operands, in contrast to Polish notation, which puts the operator in the prefix position. It is also known as Postfix notation and is parenthesis-free as long as operator arities are fixed...
. 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
Stack-oriented programming language
A stack-oriented programming language is one that relies on a stack machine model for passing parameters. Several programming languages fit this description, notably Forth, RPL, PostScript, and also many Assembly languages ....
. For example, below is a snippet of code that prints out "hello world" to the current output stream:
"hello world" print
print 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
Temporary variable
In computer programming, a temporary variable is a variable whose purpose is short-lived, usually to hold temporary data that will soon be discarded, or before it can be placed at a more permanent memory location. Because it is short-lived, it is usually declared with local scope...
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
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
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 )
dup
<body><h1><-></h1></body>
XML> ;
The word
dup duplicates the top item on the stack. The <-> stands for filling in that part of the XML document with an item from the stack.Implementation and libraries
Factor includes a large standard library, written entirely in the language. These include- A cross-platform GUI toolkit, built on top of OpenGLOpenGLOpenGL is a standard specification defining a cross-language, cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. OpenGL...
and various windowing systems, used for the development environment. - Bindings to several database libraries, including PostgreSQLPostgreSQLPostgreSQL, often simply Postgres, is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, MS Windows and Mac OS X. It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software...
and SQLiteSQLiteSQLite is an ACID-compliant embedded relational database management system contained in a relatively small C programming library. The source code for SQLite is in the public domain and implements most of the SQL standard...
. - An HTTP server and client, with the Furnace web framework.
- Efficient homogeneous arrays of integers, floats and C structs.
- A library implementing regular expressions, generating machine code to do the matching.
A foreign function interface
Foreign function interface
A foreign function interface is a mechanism by which a program written in one programming language can call routines or make use of services written in another. The term comes from the specification for Common Lisp, which explicitly refers to the language features for inter-language calls as...
is built in to Factor, allowing for communication with C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
, Objective-C
Objective-C
Objective-C is a reflective, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.Today, it is used primarily on Apple's Mac OS X and iOS: two environments derived from the OpenStep standard, though not compliant with it...
and Fortran
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
programs. There is also support for executing and communicating with shaders written in GLSL
GLSL
OpenGL Shading Language , is a high-level shading language based on the syntax of the C programming language...
.
Factor is implemented in Factor and C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
. It was originally bootstrapped from an earlier Java implementation. Today, the parser and the optimizing compiler are written in the language. Certain basic parts of the language are implemented in C++ such as the garbage collector and certain primitives.
Factor uses an image
System image
A system image in computing is a copy of the entire state of a computer system stored in some non-volatile form such as a file. A system is said to be capable of using system images if it can be shut down and later restored to exactly the same state...
-based model, analogous to many Smalltalk
Smalltalk
Smalltalk is an object-oriented, dynamically typed, reflective programming language. Smalltalk was created as the language to underpin the "new world" of computing exemplified by "human–computer symbiosis." It was designed and created in part for educational use, more so for constructionist...
implementations, where compiled code and data are stored in an image. To compile a program, the program is loaded into an image and the image is saved. A special tool assists in the process of creating a minimal image to run a particular program, packaging the result into something that can be deployed as a standalone application.
The Factor compiler implements many advanced optimizations and has been used as a target for research in new optimization techniques.