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16 Using Guile as an Extension Language

The chapters in this part of the manual explain how to use Guile as a powerful application extension language.

An important change for the 1.6.x series of Guile releases is that the GH interface is now deprecated. For the reasoning behind this decision, see See GH deprecation. The GH interface will continue to be supported for the 1.6.x and 1.8.x release series, but will be dropped thereafter, so developers are encouraged to switch progressively to the scm interface. The last chapter in this part of the manual (see GH) documents both how to use GH and how to switch from GH to scm.

The Guile developers believe that clarification of the GH vs. scm debate, and the consequent deprecation of the GH interface, are in the long term interests of the project. However it does create an unfortunate situation for developers who want to start a project using Guile and so read the manual to find out how to proceed. They will discover that the GH interface, although quite well documented, is deprecated, but that there is almost no adequate documentation for its theoretical replacement, the scm interface. Moreover, the scm interface still has the odd few rough edges which need smoothing down.

Therefore, although deprecated, it is quite OK to continue to use the GH interface if you feel uncomfortable with the `scm_' interface as it stands today. By the time that support for GH is dropped, we plan to have thoroughly documented the `scm_' interface, and to have enhanced it such that conversion from GH to the `scm_' interface will be very straightforward, and probably mostly automated.

As far as documentation of the scm interface is concerned, the current position is that it is a bit confused, but that the situation should improve rapidly once the 1.6.0 release is out. The plan is to refocus the bulk of Part II, currently "Guile Scheme", as the "Guile API Reference" so that it covers both Scheme and C interfaces. (This makes sense because almost all of Guile's primitive procedures on the Scheme level -- e.g. memq -- are also available as C level primitives in the scm interface -- e.g. scm_memq.) There will then remain a certain amount of Scheme-specific (such as the "Basic Ideas" chapter) and C-specific documentation (such as SMOB usage and interaction with the garbage collector) to collect into corresponding chapters.