TITLE: Parts of Speech in Programming Languages AUTHOR: Eugene Wallingford DATE: November 03, 2009 7:48 PM DESC: ----- BODY: I enjoyed Reg Braithwaite's talk Ruby.rewrite(Ruby) (slides available on-line). It gives a nice survey of some metaprogramming hacks related to Ruby's syntactic and semantic structure. To me, one of the most thought-provoking things Reg says is actually a rather small point in the overall message of the talk. Object-oriented programming is, he summarizes, basically a matter a matter of nouns and verbs, objects and their behaviors. What about other parts of speech? He gives a simple example of an adverb:
In this expression, not is an adverb that modifies the behavior of blank?. At the syntactic level, we are really telling blitz to behave differently in response to the next message, which happens to be blank?, but from the programmer's semantic level not modifies the predicate blank?. It is an adverb! Reg notes that some purists might flag this code as a violation of the Law of Demeter, because it sends a message to an object received from another message send. But it doesn't! It just looks that way at the syntax level. We aren't chaining two requests together; we are modifying how one of the requests works, how its result is to be interpreted. While this may look like a violation of the Law of Demeter, it isn't. Being able to talk about adverbs, and thus to distinguish among different kinds of message, helps to make this clear. It also helps us to program better in at least two ways. First, we are able to use our tools without unnecessary guilt at breaking the letter of a law that doesn't really apply. Second, we are freed to think more creatively about how our programs can say what we mean. I love that Ruby allows me to create constructs such as not and weave them seamlessly into my code. Many of my favorite gems and apps use this feature to create domain-specific languages that look and feel like what they are and look and feel like Ruby -- at the same time. Treetop is an example. I'd love to hear about your favorite examples. So, our OO programs have nouns and verbs and adverbs. What about other parts of speech? I can think of at least two from Java. One is pronouns. In English, this is a demonstrative pronoun. It is in Java, too. I think that super is also demonstrative pronoun, though it's not a word we use similarly in English. As an object, I consist of this part of me and that (super) part of me. Another is adjectives. When I teach Java to students, I usually make an analogy from access modifiers -- public, private, and protected -- to adjectives. They modify the variables and methods which they accompany. So do synchronized and volatile. Once we free ourselves to think this way, though, I think there is something more powerful afoot. We can begin to think about creating and using our own pronouns and adjectives in code. Do we need to say something in which another part of speech helps us to communicate better? If so, how can we make it so? We shouldn't be limited to the keywords defined for us five or fifteen or fifty years ago. Thinking about adverbs in programming languages reminds me of a wonderful Onward! talk I heard at the OOPSLA 2003 conference. Cristina Lopes talked about naturalistic programming. She suggested that this was a natural step in the evolution from aspect-oriented programming, which had delocalized references within programs in a new way, to code that is concise, effective, and understandable. Naturalistic programming would seek to take advantage of elements in natural language that humans have been using to think about and describe complex systems for thousand of years. I don't remember many of the details of the talk, but I recall discussion of how we could use anaphora (repetition for the sake of emphasis) and temporal references in programs. Now that my mind is tuned to this wavelength, I'll go back to read the paper and see what other connections it might trigger. What other parts of speech might we make a natural part of our programs? (While writing this essay, I have felt a strong sense of deja vu. Have I written a previous blog entry on this before? If so, I haven't found it yet. I'll keep looking.) -----