5.7.4 A Choice of Programming Options

The preceding arguments and example point to a model of Guile programming that is applicable in many cases. According to this model, Guile programming involves a balance between C and Scheme programming, with the aim being to extract the greatest possible Scheme level benefit from the least amount of C level work.

The C level work required in this model usually consists of packaging and exporting functions and application objects such that they can be seen and manipulated on the Scheme level. To help with this, Guile’s C language interface includes utility features that aim to make this kind of integration very easy for the application developer. These features are documented later in this part of the manual: see REFFIXME.

This model, though, is really just one of a range of possible programming options. If all of the functionality that you need is available from Scheme, you could choose instead to write your whole application in Scheme (or one of the other high level languages that Guile supports through translation), and simply use Guile as an interpreter for Scheme. (In the future, we hope that Guile will also be able to compile Scheme code, so lessening the performance gap between C and Scheme code.) Or, at the other end of the C–Scheme scale, you could write the majority of your application in C, and only call out to Guile occasionally for specific actions such as reading a configuration file or executing a user-specified extension. The choices boil down to two basic questions:

• Which parts of the application do you write in C, and which in Scheme (or another high level translated language)?
• How do you design the interface between the C and Scheme parts of your application?

These are of course design questions, and the right design for any given application will always depend upon the particular requirements that you are trying to meet. In the context of Guile, however, there are some generally applicable considerations that can help you when designing your answers.