Designing with minilanguages involves two distinct challenges. One is having existing minilanguages handy in your toolkit, and recognizing when they can be applied as-is. The other is knowing when it is appropriate to design a custom minilanguage for an application. To help you develop both aspects of your design sense, about half of this chapter will consist of case studies.
In Chapter6 we looked at sng(1), which translates between PNG and an editable all-text representation of the same bits. The SNG data-file format is worth reexamining for contrast here because it is not quite a domain-specific minilanguage. It describes a data layout, but doesn't associate any implied sequence of actions with the data.
SNG does, however, share one important characteristic with domain-specific minilanguages that binary structured data formats like PNG do not — transparency. Structured data files make it possible for editing, conversion, and generation tools to cooperate without knowing about each others' design assumptions other than through the medium of the minilanguage. What SNG adds is that, like a domain-specific minilanguage, it's designed to be easy to parse by eyeball and edit with general-purpose tools.
