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//[[Documentation]] *Hyperlinks and hypergraphs LMNtal links represent point-to-point connection between atoms and form an ordinary graph. In some applications, however, we may want '''hyperlinks''', namely links that interconnect more than two atoms. A graph structure with hyperlinks forms a '''(hierarchical) hypergraph'''. LMNtal provides syntax and operations for hypergraphs, which will be described below. Currently, hyperlinks are supported by the '''SLIM''' runtime running in the '''ordinary''' (as opposed to non-deterministic) execution mode. **Creating a hyperlink A hyperlink is created by a ''new'' construct specified in a guard. hoge. hoge :- new($h) | a($h), b($h). --> a(!1), b(!1). Each hyperlink is given a fresh private name, which will be printed as a "''!''" followed by a hexadecimal number. **Type checking The type constraint ''hlink''($x) checks if $x represents a hyperlink. main. main :- new($x) | a($x). a($x) :- hlink($x) | b($x). --> b(!1). **Equality checking An occurrence of a hyperlink is regarded as a unary atom with a special, private name. Therefore, the constructs ''=='' and ''\='' can be used for comparing two hyperlinks, e.g., a($x), b($y) :- hlink($x), hlink($y), $x == $y | ok. The above rule can be written also as a($x), b($x) :- ok. **Fusing two hyperlinks Two hyperlinks can be fused into one using the "''><''" operator. main. main :- new($x), new($y) | a($x), b($y). a($x), a($y) :- $x \= $y | a($x), b($y), $x >< $y. If $x and $y represent different hyperlinks (i.e., have different hyperlink names), they will be merged into one; that is, they are made to have the same hyperlink name. **Number of occurrences The ''num'' construct in a guard will return the number of occurrences of the specified hyperlink. main. main :- new($x) | a($x), b($x). a($h) :- $n = num($h) | number($n). --> b(!1), number(2). Another use: main. main :- new($x) | a($x). a($h) :- $n = num($h), $n < 5 | a($h), a($h). --> a(!1), a(!1), a(!1), a(!1), a(!1). Yet another use: main :- new($x) | flag(!x), a(!x), a(!x), a(!x), a(!x). a($h) :- hlink($h) | . flag($h) :- $n = num($h), $n =:= 1 | ok. --> ok. // ok is created when all a(!1)'s are removed In this way, using hyperlinks, one can check the '''absence''' of a particular hyperlink. *How to use **LaViT When you execute your program under LaViT (recommended), select the Option tab and turn on the following checkboxes: - Slimcode Compile Option: ''--slimcode'' and ''--hl-opt'' - Slim Option: ''--hl'' Please see below for the details of those options. **Compiling Currently, programs with hyperlinks can be executed only under SLIM. To compile them, both ''--slimcode'' and ''--hl'' (or ''--hl-opt'') options need be specified, e.g., lmntal --slimcode --hl hoge.lmn > hoge.il - ''--hl'' : turn on hyperlinks. - ''--hl-opt'' : turn on hyperlinks and optimize graph matching using hyperlink connection. **Execution Specify ''--hl'' when running SLIM, e.g., slim --hl --show-hl hoge.il - ''--hl'' : turn on hyperlinks -- currently, this cannot be specified with ''-nd''. - ''--show-hl'' : prints the details of hyperlinks. -- Without this option, different occurrences of a hyperlink are printed with the same name. -- With this option, each occurrence of a hyperlink is printed with its own ID. In addition, a table of hyperlink occurrences will be printed.
