C--

C-- (pronounced cee minus minus) is a C-like programming language. Its creators, functional programming researchers Simon Peyton Jones and Norman Ramsey[1][2], designed it to be generated mainly by compilers for very high-level languages rather than written by human programmers. Unlike many other intermediate languages, its representation is plain ASCII text, not bytecode or another binary format.

Design

C-- is a "portable assembly language", designed to ease the task of implementing a compiler which produces high quality machine code. This is done 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 guarantee tail call optimization, or support 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 functions, 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-like languages, "--" and "++" are operators meaning "decrement" and "increment".)

C-- is a target platform for the Glasgow Haskell Compiler.[3] Some of C--'s developers, including Simon Peyton Jones, João Dias, and Norman Ramsey, work or have worked on the Glasgow Haskell Compiler.

Type system

The C-- type system 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.

See also

References

  1. ^ Nordin, Thomas; Jones, Simon Peyton; Iglesias, Pablo Nogueira; Oliva, Dino (1998-04-23). "The C– Language Reference Manual".
  2. ^ Reig, Fermin; Ramsey, Norman; Jones, Simon Peyton (1999-01-01). "C–: a portable assembly language that supports garbage collection".
  3. ^ "An improved LLVM backend".

External links