Basic Use

Although the define interface form provides a fairly rich sublanguage for specifying interfaces, it is often sufficient to use just the “minimal” form. For example, if gc.h contained the following code:

typedef char bool;
typedef struct obj obj_t;
typedef char *str;
extern obj_t alloc(obj_t class, int bytes);
extern void scavenge(obj_t *addr);
extern obj_t transport(obj_t obj, int bytes);
extern void shrink(obj_t obj, int bytes);
extern void collect_garbage(void);
extern bool TimeToGC;
#define ForwardingMarker ((obj_t)(0xDEADBEEF))

then you could import it by creating a file named class.intr which includes arbitrary Dylan code and the following:

define interface
   #include "gc.h";
end interface;

You would then run melange class.intr class.dylan which would produce a file of Dylan code which contains appropriate definitions for the classes <bool>, <obj>, <obj_t>, and <str>; the variable TimeToGC; and the functions alloc, scavenge, transport, shrink, and collect_garbage. (The constant ForwardingMarker will be excluded because it is not a simple literal.)

if (TimeToGC() ~= 0)
   collect_garbage();
end if;

This code fragment points out some of the hazards of “simple” imports. Melange has no way of knowing that bool should correspond to Dylan’s <boolean> class, so you are stuck with a simple integer. Likewise, the system wouldn’t be able to guess that char * should correspond to the Dylan class <c-string>. We will explain in later sections how “map:” or “equate:” options may be used to provide this information to Melange.