C--
Encyclopedia
C-- is a C
-like programming language
. Its creators, functional programming
researchers Simon Peyton Jones
and Norman Ramsey, designed it to be generated mainly by compiler
s for very high-level languages rather than written by human programmers. Unlike many other intermediate language
s, its representation is plain ASCII
text, not bytecode
or another binary format.
", designed to ease the task of implementing a compiler which produces high-quality machine code by having the compiler generate C-- code, delegating the harder work of low-level code generation and optimisation to a C-- compiler.
Work on C-- began in the late 1990s. Since writing a custom code generator is a challenge in itself, and the compiler back ends available to researchers at that time were complex and poorly documented, several projects had written compilers which generated C
code (for instance, the original Modula-3
compiler). However, C is a poor choice for functional languages: it does not support tail recursion, accurate garbage collection
or efficient exception handling
. C-- is a simpler, tightly-defined alternative to C which does support all of these things. Its most innovative feature is a run-time interface which allows writing of portable garbage collectors, exception handling systems and other run-time features which work with any C-- compiler.
The language's syntax borrows heavily from C. It omits or changes standard C features such as variadic function
s, pointer syntax
, and aspects of C's type system
, because they hamper certain essential features of C-- and the ease with which code-generation tools can produce it.
The name of the language is an in-joke, indicating that C-- is a reduced form of C, in the same way that C++
is basically an expanded form of C. (In C and C++, "--" and "++" are operators meaning "subtract 1 from" and "add 1 to".)
C-- is a target platform for the Glasgow Haskell Compiler
, and an adaptation of C-- will eventually become the main code-generation path. Some of C--'s developers, including Simon Peyton Jones
, João Dias, and Norman Ramsey, also work or have worked on the Glasgow Haskell Compiler. The GHC codebase and development are based at Microsoft Research
in Cambridge
, though it is not a Microsoft
project.
is deliberately designed to reflect constraints imposed by hardware rather than conventions imposed by higher-level languages. In C-- a value stored in a register or memory may have only one type: bit vector. However, bit vector is a polymorphic
type and may come in several widths, e.g., bits8, bits32, or bits64. In addition to the bit-vector type C-- also provides a Boolean type bool, which can be computed by expressions and used for control flow but cannot be stored in a register or in memory. As in an assembly language, any higher type discipline, such as distinctions between signed, unsigned, float, and pointer, is imposed by the C-- operators or other syntactic constructs in the language.
computers. Sphinx C-- mixes C with x86 assembly language.
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....
-like 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....
. Its creators, functional programming
Functional 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...
researchers Simon Peyton Jones
Simon Peyton Jones
Simon Peyton Jones is a British computer scientist who researches the implementation and applications of functional programming languages, particularly lazy functional languages...
and Norman Ramsey, designed it to be generated mainly by compiler
Compiler
A compiler is a computer program that transforms source code written in a programming language into another computer language...
s for very high-level languages rather than written by human programmers. Unlike many other intermediate language
Intermediate language
In computer science, an intermediate language is the language of an abstract machine designed to aid in the analysis of computer programs. The term comes from their use in compilers, where a compiler first translates the source code of a program into a form more suitable for code-improving...
s, its representation is plain ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
text, not bytecode
Bytecode
Bytecode, also known as p-code , is a term which has been used to denote various forms of instruction sets designed for efficient execution by a software interpreter as well as being suitable for further compilation into machine code...
or another binary format.
Design
C-- is a "portable assembly languageAssembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
", designed to ease the task of implementing a compiler which produces high-quality machine code by having the compiler generate C-- code, delegating the harder work of low-level code generation and optimisation to a C-- compiler.
Work on C-- began in the late 1990s. Since writing a custom code generator is a challenge in itself, and the compiler back ends available to researchers at that time were complex and poorly documented, several projects had written compilers which generated 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....
code (for instance, the original Modula-3
Modula-3
In computer science, Modula-3 is a programming language conceived as a successor to an upgraded version of Modula-2 known as Modula-2+. While it has been influential in research circles it has not been adopted widely in industry...
compiler). However, C is a poor choice for functional languages: it does not support tail recursion, accurate garbage collection
Garbage collection (computer science)
In computer science, garbage collection is a form of automatic memory management. The garbage collector, or just collector, attempts to reclaim garbage, or memory occupied by objects that are no longer in use by the program...
or efficient exception handling
Exception handling
Exception handling is a programming language construct or computer hardware mechanism designed to handle the occurrence of exceptions, special conditions that change the normal flow of program execution....
. C-- is a simpler, tightly-defined alternative to C which does support all of these things. Its most innovative feature is a run-time interface which allows writing of portable garbage collectors, exception handling systems and other run-time features which work with any C-- compiler.
The language's syntax borrows heavily from C. It omits or changes standard C features such as variadic function
Variadic function
In computer programming, a variadic function is a function of indefinite arity, i.e., one which accepts a variable number of arguments. Support for variadic functions differs widely among programming languages....
s, pointer syntax
Syntax
In linguistics, syntax is the study of the principles and rules for constructing phrases and sentences in natural languages....
, and aspects of C's type system
Type system
A type system associates a type with each computed value. By examining the flow of these values, a type system attempts to ensure or prove that no type errors can occur...
, because they hamper certain essential features of C-- and the ease with which code-generation tools can produce it.
The name of the language is an in-joke, indicating that C-- is a reduced form of C, in the same way that 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...
is basically an expanded form of C. (In C and C++, "--" and "++" are operators meaning "subtract 1 from" and "add 1 to".)
C-- is a target platform for the Glasgow Haskell Compiler
Glasgow Haskell Compiler
The Glorious Glasgow Haskell Compilation System, more commonly known as the Glasgow Haskell Compiler or GHC, is an open source native code compiler for the functional programming language Haskell. The lead developers are Simon Peyton Jones and Simon Marlow...
, and an adaptation of C-- will eventually become the main code-generation path. Some of C--'s developers, including Simon Peyton Jones
Simon Peyton Jones
Simon Peyton Jones is a British computer scientist who researches the implementation and applications of functional programming languages, particularly lazy functional languages...
, João Dias, and Norman Ramsey, also work or have worked on the Glasgow Haskell Compiler. The GHC codebase and development are based at Microsoft Research
Microsoft Research
Microsoft Research is the research division of Microsoft created in 1991 for developing various computer science ideas and integrating them into Microsoft products. It currently employs Turing Award winners C.A.R. Hoare, Butler Lampson, and Charles P...
in Cambridge
Cambridge
The city of Cambridge is a university town and the administrative centre of the county of Cambridgeshire, England. It lies in East Anglia about north of London. Cambridge is at the heart of the high-technology centre known as Silicon Fen – a play on Silicon Valley and the fens surrounding the...
, though it is not a Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
project.
Type system
The C-- type systemType system
A type system associates a type with each computed value. By examining the flow of these values, a type system attempts to ensure or prove that no type errors can occur...
is deliberately designed to reflect constraints imposed by hardware rather than conventions imposed by higher-level languages. In C-- a value stored in a register or memory may have only one type: bit vector. However, bit vector is a polymorphic
Type polymorphism
In computer science, polymorphism is a programming language feature that allows values of different data types to be handled using a uniform interface. The concept of parametric polymorphism applies to both data types and functions...
type and may come in several widths, e.g., bits8, bits32, or bits64. In addition to the bit-vector type C-- also provides a Boolean type bool, which can be computed by expressions and used for control flow but cannot be stored in a register or in memory. As in an assembly language, any higher type discipline, such as distinctions between signed, unsigned, float, and pointer, is imposed by the C-- operators or other syntactic constructs in the language.
Sphinx C--
The name "C--" was also used for an earlier programming language developed in the 1990s by Peter Cellik for x86X86 architecture
The term x86 refers to a family of instruction set architectures based on the Intel 8086 CPU. The 8086 was launched in 1978 as a fully 16-bit extension of Intel's 8-bit based 8080 microprocessor and also introduced segmentation to overcome the 16-bit addressing barrier of such designs...
computers. Sphinx C-- mixes C with x86 assembly language.