[Code]
As feature structures get updated, reference chains tend to get very
long and thus slower to process. ALE remedies this situation by
performing an operation called path compression to reduce the
size of reference chains before an edge is added to a chart and before
a feature structure is output to the user. The predicate
fully_deref/4 is responsible for path compression.
| Condition | Action |
| RefIn is a variable | RefIn = fully(TagOut,SVsOut)-SVsOut, run
fully_deref/4 on arguments of RefIn |
| RefIn is not a variable | if RefIn = fully(Tag,_), then
TagOut = Tag and SVsOut = SVs |
if RefIn == Tag-SVs, then call
fully_deref(Tag,SVs,TagOut,SVsOut. |
As an example, consider the following:
| ?- fully_deref(Tag1-s1(Tag2-t2-t3,Tag3-t4-t5),
SVsIn,TagOut,SVsOut).
Tag1 = fully(TagOut,s1(_A-t2,_B-t4))-s1(_A-t2,_B-t4),
Tag2 = fully(_A,t2)-t2,
Tag3 = fully(_B,t4)-t4,
SVsOut = s1(_A-t2,_B-t4)
The result of running path-compression on
Tag1-s1(Tag2-t2-t3,Tag3-t4-t5)is
TagOut-SVsOut. The
reason for using fully/2 is that we want to know if a path has
already been compressed or not due to cycles in the feature structure
that it represents.