Gentle tries to cover most tasks of compiler writing within a high-level uniform framework. However, there are also tasks for which languages like C are better suited.
Gentle allows the user to implement types and predicates in C, but use them as if they were implemented in Gentle.
The Gentle system comes with some ready-to-use C types and functions that are accessible in this way. The mechanism may also be applied by the user to build his or her own external types and functions.