[Haskell-cafe] Re: What *is* a DSL?

[Emil Axelsson]

Ben Franksen skrev:
> minh thu wrote:
>> 2009/10/7 Günther Schmidt <gue.schmidt at web.de>:
>>>> I've informally argued that a true DSL -- separate from a good API --
>>>> should have semantic characteristics of a language: binding forms,
>>>> control structures, abstraction, composition. Some have type systems.
>>>>
>>> That is one requirement that confuses me, abstraction.
>>>
>>> I thought of DSLs as "special purpose" languages, ie. you give your DSL
>>> everything it needs for that purpose.
>>>
>>> Why would it also need the ability to express even further abstractions,
>>> it is supposed to *be* the abstraction.
>> Programming abstractions at the DSL level, not to further abstract
>> what the DSL covers.
>>
>> Functions, for instance, are typical abstraction means offered by
>> programming languages. Even if your language is specific to some
>> domain, being able to create your own functions, and not only rely on
>> those provided by the DSL implementation, is important.
>>
>> Imagine a (E)DSL for 3D programming (e.g. shading language): the
>> language is designed to fit well the problem (e.g. in this case, 3D
>> linear algebra, color operations, ...) but you'll agree it would be a
>> shame to not be able to provide your own functions.
> 
> But isn't one of the advantages of an _E_DSL that we can use the host
> language (Haskell) as a meta or macro language for the DSL? I would think
> that this greatly reduces the need to provide abstraction
> facilities /inside/ the DSL. In fact most existing (and often cited
> examples of) EDSLs in Haskell do not provide abstraction.

I would say that the DSL is what the user sees. In this view, I think 
it's correct to say that many (or most) DSLs need function abstraction. 
Whether or not the internal data structure has function abstraction is 
an implementation detail.

/ Emil