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13.3 Return values

Some general conventions for return values are worth mentioning:

The words “success” and “failure” are heavily overloaded in these documents. But in contexts where our meaning is clear we will usually abbreviate “method success” and “method failure” to “success” and “failure”, respectively.

The Libmarpa programmer should not overly rely on the general conventions for return values. In particular, -2 may sometimes be ambiguous — both a valid return value for method success, and a potential indication of hard method failure. In this case, the programmer must distinguish the two return statuses based on the error code, and a programmer who is relying too heavily on the general conventions will fall into a trap. For a the description of the return values of marpa_g_rule_rank_set(), see Rank methods.