Desugared

Desugared refers to code that has been transformed from its syntactic sugar into a more explicit, lower‑level form using primitive constructs of the language. Syntactic sugar comprises language features that make code easier to read or write but have the same semantics as more explicit constructs.

Desugaring is typically performed by a compiler or preprocessor as part of a lowering or desugaring phase. The goal is to simplify subsequent stages of compilation by reducing the set of language constructs the rest of the pipeline must handle and to produce a uniform core language representation for analysis and optimization.

Examples of desugaring across languages include:

- Haskell: A do-block is desugared into a sequence of monadic binds using the (>>=) operator and return. List comprehensions desugar to map and filter operations over lists.

- Scala: For-comprehensions desugar into combinations of flatMap, map, and withFilter, yielding the same semantics as the original comprehension.

- JavaScript: Destructuring assignments and certain arrow-function forms can be desugared into explicit variable assignments and function expressions, respectively; transpilers often desugar newer syntax to older runtime targets.

- Other languages: Features such as pattern matching, optional chaining, or range expressions can also be desugared into primitive constructs to facilitate uniform handling by later stages of a compiler.

Note on semantics: Desugaring preserves the program’s semantics, though it can affect source-level diagnostics and debugging experiences. It is distinct from optimization; its purpose is to simplify and standardize the representation of code in the compiler pipeline.