Hyperlinks (slim)
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 and form a hypergraph.
LMNtal provides syntax and operations for hypergraphs, which will be described below. Currently, hyperlinks are supported by the slim runtime
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($h).
*--> a(!1), b(!1).
Type checking for hyperlinks
a(!1).
a($x) :- hlink($x) | b($x).
*--> b(!1).
Merging two hyperlinks
- Two hyperlinks can be merged into one using the "><" operator.
a(!1), b(!2).
a($x), a($y) :- $x \= $y | a($x), b($y), $x >< $y.
- If $x and $y represent different hyperlinks, they will be merged into one.
Number of occurrences
- The "num" construct in a guard will return the number of occurrences of the specified hyperlink.
a(!1), b(!1).
a($h) :- $n = num($h) | number($n).
*--> b(!1), number(2).
- Another use
a(!1).
a($h) :- $n = num($h), $n < 5 | a($h), a($h).
*--> a(!1), a(!1), a(!1), a(!1), a(!1).
- Yet another use
flag(!1), a(!1), a(!1), a(!1), a(!1).
a($h) :- hlink($h) | .
flag($h) :- $n = num($h), $n =:= 1 | ok.
*--> ok. // ok is created when all a(!1)'s are removed
- Thus, using hyperlinks, one can check the absence of a particular atom.
Guard Library
The following type constraints can be used in guards.
The + (input) sign preceding a process context name means that the name should
appear in the head, while the - (output) sign means that the name should not
appear in the head.
- '='(+$u,-$v)
- make sure that $u[X] and $v[Y] are unary atoms with the same name.
- '='(-$u,+$v)
- same as above.
- '=='(+$u,+$v)
- check if $u[X] and $v[Y] are unary atoms with the same name.
- unary(+$u)
- check if $u[X] is a unary atom.
- ground(+$g)
- check if $g[X1,...,Xn] (n>0) is a connected graph whose free links are exactly X1,...,Xn.
- int(+$i)
- check if $i[X] is an integer.
- float(+$f)
- check if $f[X] is a floating-point number.
- int(+$float,-$int)
- cast.
- float(+$int,-$float)
- cast.
- 345(-$int)
- defined for every integer (not only with 345).
- '-3.14'(-$float)
- defined for every float.
- '<'(+$int,+$int)
- integer comparison; also: '>', '=<', '>=', '=:=', '=\='.
- '+'(+$int,+$int,-$int)
- integer operation; also: '-', '*', '/', mod.
- '<.'(+$float,+$float)
- float comparison; also: '>.', '=<.', '>=.', '=:=.', '=\=.'.
- '+.'(+$float,+$float,-$float)
- float operation; also: '-.', '*.', '/.'.
- uniq(+$g1,...,+$gn)
- uniqueness constraint; checks if the rule has not been applied to the tuple $g1[X1], ..., $gn[Xn] (n>=0).
![[PukiWiki]](lmntal_220x80.png "[PukiWiki]")
