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

[minh thu]

2009/10/7 Ben Franksen <ben.franksen at online.de>:
> 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?

It is.

> 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.

Even when you have good macro supports, you don't code everything at
the macro level. But it all depends on the particular EDSL we talk
about. If the EDSL is close to a regular programming language, it is
likely to provide the ability to create functions.

Cheers,
Thu