Adtpp: lightweight efficient safe polymorphic algebraic data
types for C
Lee Naish, Peter Schachte and Aleck MacNally
Adtpp is an open-source tool that adds support for algebraic data types
(ADTs) to the C programming language. ADTs allow more precise description
of program types and more robust handling of data structures than is
directly supported by C. ADT definitions and other declarations are put
in a file that is preprocessed by adtpp to produce a C header (".h")
file which can be included in C source files. The generated header file
contains C type definitions, macros, and inline functions that support
type-safe construction, deconstruction, and pattern matching of ADT
values, while avoiding unsafe operations such as casts, and avoiding
the risk of errors such as dereferencing NULL pointers and accessing
inappropriate fields of unions. Values are represented efficiently,
using techniques from the implementation of declarative languages.
For many simple data types, the representation is identical to a direct
implementation in C, with no loss of efficiency. For more complex
types, the adtpp representation is more efficient than common C
representations, while preserving type safety and convenience. As an
example, we present a new variation of 234-trees which is very compact.
Adtpp also supports parametric polymorphism such as defining a type
"list of t", where t can be any ADT, and generic functions
such as length. However, compared to typical declarative languages,
polymorphic code is somewhat more verbose, due to our reliance on the
limited type checking available in C.
A version of this paper with minor changes is to appear in Software
Practice and Exerience.
Algebraic data types, C language extension, generics,
polymorphism, safety, static checking, open-source