Trace-Alts

The function trace-alts systematically monitors traversing of alts in the grammar, even if the alts are not traced, and outputs a message whenever a new branch is tried. It is best used in conjunction with a trace-disable-all setting, to follow uniquely alt traversal. The form of the output is as follows:

          


LISP> (trace-disable-all)
LISP> (trace-alts)
LISP> (uni t1)


>========================================
>STARTING CAT CLAUSE AT LEVEL {}
>========================================


>Fail in alt VOICE
>Fail in alt VOICE-NORMAL
>Fail in alt VOICE-NORMAL
>Fail in alt VOICE-NORMAL
>Fail in alt DATIVE-MOVE-DEFAULT
>Fail in alt DATIVE-MOVE-DEFAULT
>Fail in alt SUBJECT-SUBCAT
>Fail in alt SUBJ-COMP-CAT
>Fail in alt :ANONYMOUS
>Fail in alt :ANONYMOUS
>Expanding constituent {} into cset ({SYNT-ROLES SUBJ-COMP}
                                     {PROCESS}
                                     {SYNT-ROLES SUBJECT}).
>
          
          

Each time a branch in an alt fails, the message ``fail in alt X'' is printed. If the alt is not traced, the name :anonymous is printed instead. This is useful to find possible errors even in places which are not traced in the grammar. In general, trace-alt should only be used in last recourse.