This post originated from an RSS feed registered with Agile Buzz by James Robertson. Original Post: Does not understand Feed Title: Michael Lucas-Smith Feed URL: http://www.michaellucassmith.com/site.atom Feed Description: Smalltalk and my misinterpretations of life Latest Agile Buzz Posts Latest Agile Buzz Posts by James Robertson Latest Posts From Michael Lucas-Smith

Does Not Understand in Smalltalk is a complex beasty. It's a very powerful tool, yes, but it comes at a cost. What is that cost? It's a new meta-construct that isn't part of the language and is therefore not supported by the tools.

So what IS DNU all about? Why do we even have it if it can cause so much trouble. Well, it's basic premise is that you can extend the language beyond what it was originally intended to do.

For example, you can make any is* method that isn't understand be converted in to isAClassName to do a isKindOf: for you. That puts a new semantic meaning on any method beginning with is* which may or may not be good for the language.

We're making this new meta-construct and we know that none of the tools will understand that construct. The tools are smart enough to deal with it and let you debug it, inspect it, track it, etc - but they will never 'grok' its meaning.

Also, we have to consider the implications of speed. When we're using DNU, the VM does not know how to optimise what we're doing, because it too doesn't 'grok' what we're trying to achieve. We're circumventing the normal assumptions about how the language will work.

So. I propose that the true purpose of DNU is to explore language constructs that are not part of the original Smalltalk-80 and are not something you can merely extend or add a class to achieve. Syntactical sugars in fact - such as being able to write XML directly in to the system and have it 'execute'.. being able to pass as many arguments to a function as you want without implementing a variant of each call... being able to use named-parameters instead of keyword-selectors.

At some point, some one needs to review these constructs and decide if they are worthwhile or not to be put in to the language. Smalltalk has never ever done this, because it usually cheap enough to leave it as a DNU. Languages like perl, ruby, python do it all the time - except that they cannot prototype the functionality in existing features in their language before they leap in head first to add the new language feature.