Compiler Description Language

Compiler Description Language, or CDL, is a programming language based on affix grammars. It is very similar to Backus–Naur form (BNF) notation. It was designed for the development of compilers. It is very limited in its capabilities and control flow; and intentionally so. The benefits of these limitations are twofold. On the one hand they make possible the sophisticated data and control flow analysis used by the CDL2 optimizers resulting in extremely efficient code. The other benefit is that they foster a highly verbose naming convention. This in turn leads to programs that are to a great extent self-documenting.

The language looks a bit like Prolog (this is not surprising since both languages arose at about the same time out of work on affix grammars). As opposed to Prolog however, control flow in CDL is deterministically based on success/failure i.e., no other alternatives are tried when the current one succeeds. This idea is also used in parsing expression grammars.

CDL3 is the third version of the CDL language, significantly different from the previous two versions.

The original version, designed by Cornelis H. A. Koster at the University of Nijmegen emerged in 1971 had a rather unusual concept: it had no core. A typical programming language source is translated to machine instructions or canned sequences of those instructions. Those represent the core, the most basic abstractions that the given language supports. Such primitives can be the additions of numbers, copying variables to each other and so on. CDL1 lacks such a core, it is the responsibility of the programmer to provide the primitive operations in a form that can then be turned into machine instructions by means of an assembler or a compiler for a traditional language. The CDL1 language itself has no concept of primitives, no concept of data types apart from the machine word (an abstract unit of storage - not necessarily a real machine word as such). The evaluation rules are rather similar to the Backus–Naur form syntax descriptions; in fact, writing a parser for a language described in BNF is rather simple in CDL1.

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