Tag: meta programming
This episode is about compile-time metaprogramming, and specifically, about implementing DSLs via compile-time metaprogramming. Our guest, Laurence Tratt, illustrates the idea with his (research) programming language called Converge.
We started by talking about the importance of a custom syntax for DSL and took a brief look at the definition of DSLs by a chap called Paul Hudak. We then briefly covered the disctinction between internal and external DSLs.
More to the point of this episode, we discussed the concept of compile-time metaprogramming, and the language features necessary to achieve it: in converge, these concepts are called splice, quasi-quote and insertion. We then looked at how the Converge compiler works, and at the additional features that are required to implement DSLs based on the metaprogramming features mentioned above. Using an example, we then walked through how to implement a simple DSL.
Looking at some of the more technical details, we discussed the difference between the parse tree and the abstract syntax tree and at different kinds of parsers – specifically, the Earley parser used by Converge. In multi-stage languages (i.e. languages that execute programs and meta programs) error reporting is important, but non trivial. We discussed how this is done in Converge. We finally looked at how to integrate Converge’s expression language into your DSL and how to package DSL definition for later use.
The last segment look at the process of implementing a DSL in converge and about some of the history and practical experience with Converge. Lessons learned from building Converge wrap up the episode.
In this episode, we’re talking to Obie Fernandez about agile DSL development in Ruby. We started our discussion by defining what a DSL is, the difference between internal and external DSLs as well as the importance of the flexibly syntax of the host language in order to make DSLs worthwhile. We then looked at a couple of real world examples for DSLs, specifically, at Business Natural Languages. We then progressed to the main part of the discussions, which centered around the features of Ruby that are important for building DSLs. These include the flexible handling of parentheses, symbols, blocks as well as literal arrays and hashes. We then discussed Ruby’s meta programming feautures and how they are important for building DSLs: instantiation, method_missing callback, class macros, top level
functions and sandboxing. Features like eval, class_eval, instance_eval and define_method are also important for DSLs in
Ruby, as well as using alias_method for simple AOP.
In this Episode we talk about dynamic languages for statically-typed minds, or in other words: which are the interesting features people should learn when they go from a langauge such as Java or C# to a language like Python or Ruby. We used Ruby as the concrete example language.
We started the discussion about important features with the concept of dynamically changing an object’s type and the idea of message passing. We then looked at the concepts of blocks and closures. Next in line is a discussion about functions that create functions as well as currying. This lead into a quick discussion about continuations. Open classes, aliasing and the relationship to AOP was next on our agenda.
We then looked considered a somewhat more engineering-oriented view and looked at the importance of testing and what are the best steps of getting from static programming to dynamic programming. Finally, we discussed a bit about the current (as of October 2006) state of dynamic languages on mainstream platforms.