Output Generation

Although nothing has yet been said about the feature equations, which is the subject of the next subsection, we assume that only matches that meet the additional constraints imposed by feature equations are considered for output. If no structural match survives feature equations checking, that matching has failed. If the process of matching lhs to inp fails, there are two alternative behaviors according to the value of a parameter^25.8. If the parameter is set to false, which is the default value, no output is generated. On the other hand, if it is set to true, then the own inp tree is copied to the output. If the process of matching succeeds, as many trees will be generated in the output as the number of possible matches obtained in the process. For a given match, the output tree is generated by substituting in the rhs tree of the metarule the occurrences of variables by the material to which they have been instantiated in the match. The case of the typed-variable is simple. The name of the variable is just substituted by the name of the node to which it has been instantiated from inp. A very important detail is that the marker (foot, substitution, head, NA, or none) at the output tree node comes from what is specified in the rhs node, which can be different of the marker at the variable node in inp and of the associated node from inp. The case of the non-typed variable, not surpringly, is not so simple. In the output tree, this node will be substituted by the subtree list that was associated to this node, in the same other, attaching to the parent of this non-typed variable node. But remember, that some subtrees may have been removed from some of the trees in this list, maybe entire elements of this list, due to the effect of the children of the metavariable in lhs. It is a requirement that any occurence of a non-typed variable node at the rhs tree has exactly the same number of children than the unique occurence of this non-typed variable node in lhs. Hence, when generating the output tree, the subtrees at rhs will be inserted exactly at the points where subtrees were removed during matching, in a positional, one to one correspondance. For feature equations in the output trees see the next subsection. The comments at the output are the comments at the lhs tree of the metarule followed by the coments at inp, both parts introduced by appropriate headers, allowing the user to have a complete history of each tree.