agile software development & services

Augmenting Smalltalk with your own Control

Flow Syntax

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Hernán WilkinsonTwitter: @HernanWilkinson

Blog: objectmodels.blogspot.comwww.10pines.com

In linguistics, syntax is the set of rules, principles, and processes that govern the structure of sentences in a given language, specifically word order. The term syntax is also used to refer to the study of such principles and processes. The goal of many syntacticians is to discover the syntactic rules common to all languages.

In mathematics, syntax refers to the rules governing the behavior of mathematical systems, such as formal languages used in logic. (See logical syntax.)

Syntax

In linguistics, grammar is the set of structural rules governing the composition of clauses, phrases, and words in any given natural language. The term refers also to the study of such rules, and this field includes morphology, syntax, and phonology, often complemented by phonetics, semantics, and pragmatics.

Grammar

How easy is to change the syntax?How easy is to change the grammar?

Change

Complexity = essential + accidental

Complexity

Complexity = essential + accidental

Complexity

We can not reduce this one

Complexity = essential + accidental

Complexity

We can not reduce this one

We can definitely reduce this one

Smalltalk Complexity

One day, in a typical PARC hallway bullsession, Ted Kaehler, Dan Ingalls, and I were standing around talking about programming languages. The subject of power came up and the two of them wondered how large a language one would have to make to get great power. With as much panache as I could muster, I asserted that you could define the "most powerful language in the world" in "a page of code." They said, "Put up or shut up."

“The biggest hit for me while at SAIL in late '69 was to really understand LISP. Of course, every student knew about car, cdr, and cons, but … no one had penetrated the mysteries of eval and apply. I could hardly believe how beautiful and wonderful the idea of LISP was [McCarthy 1960]”

“… there were deep flaws in its logical foundations. By this, I mean that the pure language was supposed to be based on functions, but its most important components--such as lambda expressions, quotes, and conds--were not functions at all, and instead were called special forms”

Closure

Closure

Lisp Lambda Functions Algol-60 Block & Lexicographic binding

Scheme Closure

“with full closures you can avoid control flow syntax”

Smalltalk Syntax

object message(and other minor stuff)

if

Closure

Does not compile!

Example

(Ruby)

(Ruby)

while

Does not compile!

Closure

Closure

Boolean or Closure?

Example

exceptions

Closure

Closure

Implicit condition… why?Implicit condition… why?

In how many places is ZeroDevide handled?In how many places is SubscriptOutOfBounds handled?

Resources

file will not close if an exception signals before

Syntatically solved again

DSL

Conclusions

▶ Less syntax more flexibility▶ Less syntax more grammar▶ More grammar easier to change,

to augment!▶ Less syntax makes the language

yours!▶ Don’t be afraid! Make your own

language!

Questions?

@hernanwilkinsonHernan.wilkinson@10pines.com

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