Van Wijngaarden grammar
A Van Wijngaarden grammar (also: vW grammar or W grammar ) is a two-step from the grammar compiler program, a type of formal grammar makes it possible to define a finite set of rules potentially infinite grammars.
Application to ALGOL 68
Adriaan van Wijngaarden invented this technique and used it in the definition of the programming language ALGOL 68, in order to strictly define some syntactic requirements can, which until then had had to be formulated in natural language - for example, that identifier within its scope not declared multiple times are and that the use of the identifier matches its declaration.
A Van Wijngaarden grammar consists of a finite set of meta-rules, which are used to, from a finite set of hyper rules arbitrarily derive many production rules. Hyper rules limit the allowable contexts on the upper level. As Alain Colmerauer noted, is the consistent substitution that is used in the derivation process, substantially equivalent to the unification, as it occurs in the prologue.
Other Applications
It was found that two-stage grammars may be outside their original field of application of utility.
Anthony Fisher tried to construct a parser for general W - grammars.
It has been proposed to use the method in the ergonomics to describe complex human actions.
From the security experts Eric Filiol in a formal definition of metamorphic computer viruses compared to the two-stage grammar and Van Wijngaarden grammar was produced.