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Implementing Types and Predicates in C

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A type that is is defined without functors or a procedure that is defined without rules must be implemented in C.

Abstract types may be implemented as values of type long or as pointers.

For example, if a Gentle specification contains the declaration


'type' IDENT

this type may be implemented in a C module as


typedef struct IDENTSTRUCT *IDENT;

which defines values of type IDENT as references to structures.

Abstract procedures are implemented by C routines that take long arguments as input parameters and use (long *) arguments to realize output parameters.

For example, if a Gentle specifications defines a procedure as


'action' Max (INT, INT -> INT)

it may be implemented in C as


void Max (x, y, ref_result)
   long x;
   long y;
   long *ref_result;
{
   *ref_result = (x > y ? x : y);
}

The Gentle type INT corresponds to the C type long. Gentle terms and the type POS may also be treated as long. The Gentle type STRING corresponds to (char *).

A 'condition' must be implemented as a function returning int that yields 1 if the call succeeds and 0 if it fails.

For example, a procedure introduced by


'condition' HasMeaning (IDENT -> MEANING)

may be implemented by


int HasMeaning (id, ref_meaning)
   IDENT id;
   long *ref_meaning;
{
   if (id->meaning == 0)
      return 0;
   *ref_meaning = id->meaning;
   return 1;
}

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