Introducing the Colm Programming Language
A program is a structured object with semantics. The structure allows us to transform a program. The semantics gives us the means to compare programs and to reason about the validity of transformations. Semantics includes the extensional and intensional behaviour of a program.
Program transformation is the act of changing one program into another. The term program transformation is also used for a formal description of an algorithm that implements program transformation. The language in which the program being transformed and the resulting program are written are called the source and target languages, respectively
Adrian Thurston has recently published the first release of Colm (COmputer Language Manipulation), programming language designed for the analysis and transformation of computer languages. Adrian developed Colm during his Ph.D. at the Queen's University (ON, Canada). He explains:
A transformation language has a type system based on formal languages. Rather than define classes or data structures, one defines grammars. A parser is constructed automatically from the grammar, and the parser is used for two purposes: to parse the input language, and to parse the structural patterns in the program that performs the analysis. In this setting, grammar-based parsing is critical because it guarantees that both the input and the structural patterns are parsed into trees from the same set of types, allowing comparison.
Colm's main contribution lies in the parsing method:
Colm's parsing engine is generalized, but it also allows for the construction of arbitrary global data structures that can be queried during parsing. In other generalized methods, construction of global data requires some very careful consideration because of inherent concurrency in the parsing method. It is such a tricky task that it is often avoided altogether and the problem is deferred to a post-parse disambiguation of the parse forest.
Using Colm it is possible to get the correct parse tree on the first pass of the input, granted that some backtracking is acceptable. Colm eliminates the need to reason about concurrent updates to global data or to acquire many possible parse trees, only to throw away the incorrect ones.
Metaprogramming (a.k.a. Metamodel Oriented Programming) is making great progress thanks to the development of Language Workbenches and powerful transformation technologies such as Colm. Are you closer to use one? Are you already using one? what is your take on it?
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