Compiler Pragmas

  Compiler pragmas are compiler directives which instruct the compiler to emit a particular code type. Their syntax is similar to directives:

:- pragma(Option).

• debug - generate code which can be inspected with the debugger, similarly to setting the global flag debug_compile to on. It also implies the noexpand pragma.

• nodebug - generate optimized code with no debugger support, similarly to setting the global flag debug_compile to off. It also implies the expand pragma.

• silent_debug - generate code which cannot be inspected by the debugger, but which allows to debug predicates called by it. This is similar to setting the leash flag of all subgoals in the following clauses to notrace. This option is useful e.g. for library predicates which call other Prolog predicates: the user wants to see in the debugger the call to the library predicate and to the invoked predicate, but no internal calls in the library predicates.

• expand - do in-line expansion of some subgoals, like =/2, is/2 and others. This code can still be inspected with the debugger but the expanded subgoals look differently than in the normal debugged code, or their arguments cannot be seen. In-line expansion is also done when the global flag debug_compile is off, or when the pragma nodebug is specified.

• noexpand - inhibit the in-line goal expansion. This is also done in the pragma debug.

• skip - set the skip flag of all following predicates to on.

• noskip - set the skip flag of all following predicates to off.

• system - set the type flag of all following predicates to built_in. Moreover, all following predicates will have unspecified source_file and source_line flags.

The pragma is active from its specification in the file until the file end or until it is disabled by another pragma. Recursive compilations or calls to other compiling predicates are not affected by the pragma. Pragmas which have the same effect as global flags override the global flags if they specify more optimized code. For instance, the pragma debug has no effect if the global flag debug_compile is off, but the pragma nodebug overrides the global flag debug_compile being on.

The pragmas are useful mainly for libraries and other programs that should be always compiled in a particular mode independently of the global flags setting.