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Showing posts from April, 2012

The true role of domain specific languages

It is easy to be confused by the term domain specific language. It sounds like a fancy term for jargon. It is often interpreted to mean some form of specialized language. I would like to explore another role for them: as vehicles for policy statements.

In mathematics there are many examples of instances where it is easier to attack a problem by solving a more general, more uniform, problem and then specializing the result to get the desired answer.

It is very similar in programming: most programs take the form of a general mechanism paired with a policy that controls the machine. Taken seriously, you can see this effect down to the smallest example:
fact(n) where n>0 is n*fact(n-1);
fact(0) is 1
is a general machine for computing factorial; and the expression:fact(10) is a policy 'assertion' that specifies which particular use of the factorial machine is intended.

One important aspect of policies is that they need to be intelligible to the owner of the machine: unlike the machine…