Computing and Informatics, Vol. 35, 2016, 819{851 DEFINING C PREPROCESSOR MACRO LIBRARIES WITH FUNCTIONAL PROGRAMS Boldizs´ar Nemeth´ , M´at´e Karacsony´ Zolt´an Kelemen, M´at´e Tejfel E¨otv¨osLor´andUniversity Department of Programming Languages and Compilers H-1117 P´azm´anyP´eters´et´any1/C, Budapest, Hungary e-mail: fnboldi, kmate, kelemzol,
[email protected] Abstract. The preprocessor of the C language provides a standard way to generate code at compile time. However, writing and understanding these macros is difficult. Lack of typing, statelessness and uncommon syntax are the main reasons of this difficulty. Haskell is a high-level purely functional language with expressive type system, algebraic data types and many useful language extensions. These suggest that Haskell code can be written and maintained easier than preprocessor macros. Functional languages have certain similarities to macro languages. By using these similarities this paper describes a transformation that translates lambda expres- sions into preprocessor macros. Existing compilers for functional languages gener- ate lambda expressions from the source code as an intermediate representation. As a result it is possible to write Haskell code that will be translated into preprocessor macros that manipulate source code. This may result in faster development and maintenance of complex macro metaprograms. Keywords: C preprocessor, functional programming, Haskell, program transfor- mation, transcompiler Mathematics Subject Classification 2010: 68-N15 1 INTRODUCTION Preprocessor macros are fundamental elements of the C programming language. Besides being useful to define constants and common code snippets, they also allow 820 B. N´emeth,M. Kar´acsony,Z. Kelemen, M. Tejfel developers to extend the capabilities of the language without having to change the compiler itself.