How does a source-to-source compiler function?

A source-to-source compiler, also known as a transcompiler, translates between high-level programming languages.

A source-to-source compiler is a type of compiler that takes the source code of a program written in one programming language as its input and produces the equivalent source code in another high-level programming language. Unlike traditional compilers, which generate machine code from source code, a source-to-source compiler translates from one high-level language to another. This is why it's also often referred to as a transcompiler.

The process begins with the source-to-source compiler reading and analysing the source code to understand its structure and semantics. This is done through a process called parsing, where the source code is broken down into its constituent parts for easier analysis. The compiler then constructs an abstract syntax tree (AST), a tree representation of the source code that reflects its syntax structure according to the rules of the source language.

Once the AST is constructed, the compiler then traverses it and translates each node into the equivalent construct in the target language. This is a complex process that requires a deep understanding of both the source and target languages, as different programming languages can have vastly different syntax and semantics. The compiler must ensure that the translated code not only has the same functionality as the original code, but also adheres to the idiomatic patterns and practices of the target language.

After the translation, the compiler performs a series of optimisations to improve the efficiency and performance of the translated code. These optimisations can include things like eliminating redundant code, simplifying complex expressions, and reordering statements for better performance.

Finally, the compiler generates the translated source code in the target language. This code can then be compiled and run using a traditional compiler for the target language.

In summary, a source-to-source compiler functions by reading and analysing the source code, constructing an abstract syntax tree, translating the tree into the target language, optimising the translated code, and generating the final source code in the target language.