compiler

A compiler is a program that translates source code written in a programming language into a target representation, usually executable machine code, assembly, or an intermediate form such as bytecode. The translation aims to preserve program semantics while producing efficient code. Compilers enable software to run on different hardware platforms and to exploit performance optimizations.

A typical compiler has a front end, a middle end, and a back end. The front end performs lexical analysis and parsing, followed by semantic analysis and type checking; it builds internal structures such as a symbol table and an abstract syntax tree. The middle end applies optimizations on an intermediate representation. The back end translates the IR into target code and handles tasks like register allocation and instruction selection.

Some languages are compiled to native machine code, others to portable bytecode run by a virtual machine. There are ahead-of-time compilers and just-in-time compilers, and many systems combine both approaches. Languages such as C and C++ are usually compiled to native code, while Java and C# are typically compiled to bytecode and then JIT-compiled.

Historically, the development of compilers began in the 1950s, with early work credited to Grace Hopper and others on the first compiler for COBOL-like languages. Since then, compiler theory has shaped language design and computer architecture, enabling portability, higher-level abstractions, and aggressive optimizations. Limitations include the difficulty of ensuring correctness across optimizations, long compile times for large programs, and the challenge of generating efficient code for many architectures. See also: cross-compiler, just-in-time compilation.