{ $var-description "A logic predicate. It takes two arguments. It is true if both arguments are evaluated numerically and the first argument is less than the second, otherwise, it is false." }
{ $syntax "{ (<) X Y }" }
{ $see-also (>) (>=) (==) (=<) } ;
HELP:(=)
{ $var-description "A logic predicate. It unifies two arguments." }
{ $syntax "{ (=) X Y }" }
{ $see-also (\=) is } ;
HELP:(=<)
{ $var-description "A logic predicate. It takes two arguments. It is true if both arguments are evaluated numerically and the first argument equals or is less than the second, otherwise, it is false." }
{ $syntax "{ (=<) X Y }" }
{ $see-also (>) (>=) (==) (<) } ;
HELP:(==)
{ $var-description "A logic predicate. It tests for equality of two arguments. Evaluating two arguments, true if they are the same, false if they are different." }
{ $syntax "{ (==) X Y }" }
{ $see-also (>) (>=) (=<) (<) =:= =\= } ;
HELP:(>)
{ $var-description "A logic predicate. It is true if both arguments are evaluated numerically and the first argument is greater than the second, otherwise, it is false." }
{ $syntax "{ (>) X Y }" }
{ $see-also (>=) (==) (=<) (<) } ;
HELP:(>=)
{ $var-description "A logic predicate. It is true if both arguments are evaluated numerically and the first argument equals or is greater than the second, otherwise, it is false." }
{ $syntax "{ (>=) X Y }" }
{ $see-also (>) (==) (=<) (<) } ;
HELP:(\=)
{ $var-description "A logic predicate. It will be true when such a unification fails. Note that " { $snippet "(\\=)" } " does not actually do the unification." }
{ $syntax "{ (\\=) X Y }" }
{ $see-also (=) } ;
HELP:(\==)
{ $var-description "A logic predicate. It tests for inequality of two arguments. Evaluating two arguments, true if they are different, false if they are the same." }
{ $syntax "{ (\\==) X Y }" }
;
HELP:;;
{ $var-description "Is used to represent disjunction. The code below it has the same meaning as the code below it.
{ $description "The quotations takes an environment and returns two values. " { $snippet "=:=" } " returns the internal representation of the goal which returns t if values returned by the quotation are same numbers.\n" { $snippet "=:=" } " is intended to be used in a quotation. If there is a quotation in the definition of rule, " { $snippet "logic" } " uses the internal definition of the goal obtained by calling it." }
{ $description "The quotations takes an environment and returns two values. " { $snippet "=\\=" } " returns the internal representation of the goal which returns t if values returned by the quotation are numbers and are not same.\n" { $snippet "=\\=" } " is intended to be used in a quotation. If there is a quotation in the definition of rule, " { $snippet "logic" } " uses the internal definition of the goal obtained by calling it." }
{ $description "A multiline comment. Despite being a Prolog single-line comment, " { $link % } " is already well-known in Factor, so this variant is given instead." }
"{ appendo L{ Tom } L{ Jerry Nibbles } X } query ."
"{ appendo L{ Tom } L{ Jerry Nibbles } L{ Jerry Nibbles Tom } } query ."
"{ appendo X Y L{ Tom Jerry Nibbles } } query ."
"{ H{ { X L{ Tom Jerry Nibbles } } } }\nf\n{\n H{ { X L{ } } { Y L{ Tom Jerry Nibbles } } }\n H{ { X L{ Tom } } { Y L{ Jerry Nibbles } } }\n H{ { X L{ Tom Jerry } } { Y L{ Nibbles } } }\n H{ { X L{ Tom Jerry Nibbles } } { Y L{ } } }\n}"
}
} ;
HELP:callback
{ $values
{ "head"array } { "quot" quotation }
}
{ $description "Set the quotation to be called. Such quotations take an environment which holds the binding of logic variables, and returns t or " { $link f } " as a result of execution. To retrieve the values of logic variables in the environment, use " { $link of } " or " { $link at } "." }
{ $description "Takes a quotation and a logic variable to be unified. Each of the two quotations takes an environment and returns a value. " { $snippet "is" } " returns the internal representation of the goal.\n" { $snippet "is" } " is intended to be used in a quotation. If there is a quotation in the definition of rule, " { $snippet "logic" } " uses the internal definition of the goal obtained by calling it." } ;
{ $description "Creates a goal which uses the values of obtained logic variables. It can be used to add new rules to or drop rules from the database while a " { $link query } " is running.\nThe argument " { $snippet "quot" } " must not return any values, the created goal always return " { $link t } ".\n" { $snippet "invoke" } " is intended to be used in a quotation. If there is a quotation in the definition of rule, " { $snippet "logic" } " uses the internal definition of the goal obtained by calling it." }
{ $description "Creates a goal which uses the values of obtained logic variables. The difference with " { $link invoke } " is that " { $snippet "quot" } " returns " { $link t } " or " { $link f } ", and the created goal returns it.\n" { $snippet "invoke*" } " is intended to be used in a quotation. If there is a quotation in the definition of rule, " { $snippet "logic" } " uses the internal definition of the goal obtained by calling it." }
"{ membero Jerry L{ Tom Jerry Nibbles } } query ."
"{ membero Spike L{ Tom Jerry Nibbles } } query ."
"t\nf"
}
} ;
HELP:nlo
{ $var-description "A logic predicate. Print line breaks." }
{ $syntax "{ nlo }" }
{ $see-also writeo writenlo } ;
HELP:nonvaro
{ $var-description "A logic predicate. "{ $snippet "nonvaro" } " takes a single argument and is true if its argument is not a logic variable or is a concrete logic variable." }
{ $syntax "{ nonvaro X }" }
{ $see-also varo } ;
HELP:notrace
{ $description "Stop tracing." }
{ $see-also trace } ;
HELP:query
{ $values
{ "goal-def/defs""a goal def or an array of goal defs" }
{ "bindings-array/success?""anser" }
}
{ $description
"Inquire about the order of goals. The general form of a query is:
{ G1 G2 ... Gn } query
This G1, G2, ... Gn is a conjunction. When all of them are satisfied, it becomes " { $link t } ".
If there is only one goal, you can use its abbreviation.
G1 query
When you query with logic variable(s), you will get the answer for the logic variable(s). For such queries, an array of hashtables with logic variables as keys is returned.
{ "goal-def/defs""a goal def or an array of goal defs" } { "n/f""the highest number of responses" }
{ "bindings-array/success?""anser" }
}
{ $description "The version of " { $link query } " that limits the number of responses. Specify a number greater than or equal to 1.
If " { $link f } " is given instead of a number as " { $snippet "n/f" } ", there is no limit to the number of answers. That is, the behavior is the same as " { $link query } "." }
{ $see-also query } ;
HELP:retract
{ $values
{ "head-def""a logic predicate" }
}
{ $description "Removes the first definition that matches the given head information." }
" is a vocab for an embedded language that runs on "{ $url "https://github.com/factor/factor""Factor" } " with the capabilities of a subset of Prolog." $nl
"In the DSL, words that represent relationships are called " { $strong "logic predicates" } ". Use " { $link \ LOGIC-PRED: } " or " { $link \ LOGIC-PREDS: } " to declare the predicates you want to use. " { $strong "Logic variables" } " are used to represent relationships. use " { $link \ LOGIC-VAR: } " or " { $link \ LOGIC-VARS: } " to declare the logic variables you want to use." $nl
"In the above code, logic predicates end with the character 'o', which is a convention borrowed from miniKanren and so on, and means relation. This is not necessary, but it is useful for reducing conflicts with the words of, the parent language, Factor. We really want to write them as: " { $snippet "cat°" } ", " { $snippet "mouse°" } " and " { $snippet "creature°" } ", but we use 'o' because it's easy to type." $nl
{ $strong "Goals" } " are questions that " { $snippet "logic" } " tries to meet to be true. To represent a goal, write an array with a logic predicate followed by zero or more arguments. " { $snippet "logic" } " converts such definitions to internal representations." $nl
"The above code means that Tom is a cat and Jerry and Nibbles are mice. Use " { $link fact } " to describe the " { $strong "facts" } "." $nl
{ $unchecked-example
"{ cato Tom } query ."
"t"
} $nl
"The above code asks, \"Is Tom a cat?\". We said,\"Tom is a cat.\", so the answer is " { $link t } ". The general form of a query is:" $nl
{ $code "{ G1 G2 ... Gn } query" } $nl
"The parentheses are omitted because there was only one goal to be satisfied earlier, but here is an example of two goals:" $nl
{ $unchecked-example
"{ { cato Tom } { cato Jerry } } query ."
"f"
} $nl
"Tom is a cat, but Jerry is not declared a cat, so " { $link f } " is returned in response to this query." $nl
"If you query with logic variable(s), you will get the answer for the logic variable(s). For such queries, an array of hashtables with logic variables as keys is returned." $nl
{ $unchecked-example
"{ mouseo X } query ."
"{ H{ { X Jerry } } H{ { X Nibbles } } }"
} $nl
"The following code shows that if something is a cat, it's a creature. Use " { $link rule } " to write " { $strong "rules" } "." $nl
{ $code
"{ creatureo X } { cato X } rule"
} $nl
"According to the rules above, \"Tom is a creature.\" is answered to the following questions:" $nl
{ $unchecked-example
"{ creatureo Y } query ."
"{ H{ { Y Tom } } }"
} $nl
"The general form of " { $link rule } " is:" $nl
{ $code "Gh { Gb1 Gb2 ... Gbn } rule" } $nl
"This means " { $snippet "Gh" } " when all goals of " { $snippet "Gb1" } ", " { $snippet "Gb2" } ", ..., " { $snippet "Gbn" } " are met. This " { $snippet "Gb1 Gb2 ... Gbn" } " is a " { $strong "conjunction" } "." $nl
{ $unchecked-example
"LOGIC-PREDS: youngo young-mouseo ;
{ youngo Nibbles } fact
{ young-mouseo X } {
{ mouseo X }
{ youngo X }
} rule
{ young-mouseo X } query ."
"{ H{ { X Nibbles } } }"
} $nl
"This " { $snippet "Gh" } " is called " { $strong "head" } " and the " { $snippet "{ Gb 1Gb 2... Gbn }" } " is called " { $strong "body" } "." $nl
"Facts are rules where its body is an empty array. So, the form of " { $link fact } " is:" $nl
{ $code "Gh fact" } $nl
"Let's describe that mice are also creatures." $nl
{ $unchecked-example
"{ creatureo X } { mouseo X } rule
{ creatureo X } query ."
"{ H{ { X Tom } } H{ { X Jerry } } H{ { X Nibbles } } }"
} $nl
"To tell the truth, we were able to describe at once that cats and mice were creatures by doing the following." $nl
{ $snippet "logic" } " actually converts the disjunction in that way. You may need to be careful about that when deleting definitions that you registered using " { $link rule } ", etc." $nl
{ membero Spike [ Tom Jerry Nibbles L{ } cons cons cons ] } query ."
"t\nf"
} $nl
"Recently, they moved into a small house. The house has a living room, a dining room and a kitchen. Well, humans feel that way. Each of them seems to be in their favorite room." $nl
{ houseo T{ house { living Tom } { dining f } { kitchen Nibbles } { in-the-wall Jerry } } } fact"
} $nl
"Don't worry about not mentioning the bathroom." $nl
"Let's ask who is in the kitchen." $nl
{ $unchecked-example
"{ houseo T{ house { living __ } { dining __ } { kitchen X } { in-the-wall __ } } } query ."
"{ H{ { X Nibbles } } }"
} $nl
"These two consecutive underbars are called " { $strong "anonymous logic variables" } ". Use in place of a regular logic variable when you do not need its name and value." $nl
"It seems to be meal time. What do they eat?" $nl
{ $code
"LOGIC-PREDS: is-ao consumeso ;
SYMBOLS: mousecatmilkcheesefresh-milkEmmentaler;
{
{ is-ao Tom cat }
{ is-ao Jerry mouse }
{ is-ao Nibbles mouse }
{ is-ao fresh-milk milk }
{ is-ao Emmentaler cheese }
} facts
{
{
{ consumeso X milk } {
{ is-ao X mouse } ;;
{ is-ao X cat }
}
}
{ { consumeso X cheese } { is-ao X mouse } }
{ { consumeso X mouse } { is-ao X cat } }
} rules"
} $nl
"Here, " { $link facts } " and " { $link rules } " are used. They can be used for successive facts or rules." $nl
"Let's ask what Jerry consumes." $nl
{ $unchecked-example
"{ { consumeso Jerry X } { is-ao Y X } } query ."
"{
H{ { X milk } { Y fresh-milk } }
H{ { X cheese } { Y Emmentaler } }
}"
} $nl
"Well, what about Tom?" $nl
{ $unchecked-example
"{ { consumeso Tom X } { is-ao Y X } } query ."
"{
H{ { X milk } { Y fresh-milk } }
H{ { X mouse } { Y Jerry } }
H{ { X mouse } { Y Nibbles } }
}"
} $nl
"This is a problematical answer. We have to redefine " { $snippet "consumeso" } "." $nl
"We wrote about Tom before about common cats. What two consecutive exclamation marks represent is called a " { $strong "cut" } " operator. Use the cut operator to suppress " { $strong "backtracking" } "." $nl
"The next letter " { $link f } " is an abbreviation for goal { " { $link failo } " } using the built-in logic predicate " { $link failo } ". { " { $link failo } " } is a goal that is always " { $link f } ". Similarly, there is a goal { " { $link trueo } " } that is always " { $link t } ", and its abbreviation is " { $link t } "." $nl
"By these actions, \"Tom consumes mice.\" becomes false and suppresses the examination of general eating habits of cats." $nl
{ $unchecked-example
"{ { consumeso Tom X } { is-ao Y X } } query ."
"{ H{ { X milk } { Y fresh-milk } } }"
} $nl
"It's OK. Let's check a cat that is not Tom." $nl
{ $unchecked-example
"SYMBOL: a-cat
{ is-ao a-cat cat } fact
{ { consumeso a-cat X } { is-ao Y X } } query ."
"{
H{ { X milk } { Y fresh-milk } }
H{ { X mouse } { Y Jerry } }
H{ { X mouse } { Y Nibbles } }
}"
} $nl
"Jerry, watch out for the other cats." $nl
"So far, we've seen how to define a logic predicate with " { $link fact } ", " { $link rule } ", " { $link facts } ", and " { $link rules } ". Each time you use those words for a logic predicate, information is added to it." $nl
"You can clear these definitions with " { $link clear-pred } " for a logic predicate." $nl
{ $unchecked-example
"cato clear-pred
mouseo clear-pred
{ creatureo X } query ."
"f"
} $nl
{ $link fact } " and " { $link rule } " add a new definition to the end of a logic predicate, while " { $link fact* } " and " { $link rule* } " add them first. The order of the information can affect the results of a query." $nl
"{ H{ { Y Nibbles } } H{ { Y Jerry } } }\n{ H{ { Y Tom } } H{ { Y Nibbles } } }"
} $nl
"While " { $link clear-pred } " clears all the definition information for a given logic predicate, " { $link retract } " and " { $link retract-all } " provide selective clearing." $nl
{ $link retract } " removes the first definition that matches the given head information." $nl
{ $unchecked-example
"{ mouseo Jerry } retract
{ mouseo X } query ."
"{ H{ { X Nibbles } } }"
} $nl
"On the other hand, " { $link retract-all } " removes all definitions that match a given head goal definition. Logic variables, including anonymous logic variables, can be used as goal definition arguments in " { $link retract } " and " { $link retract-all } ". A logic variable match any argument." $nl
{ $unchecked-example
"{ mouseo Jerry } fact
{ mouseo X } query .
{ mouseo __ } retract-all
{ mouseo X } query ."
"{ H{ { X Nibbles } } H{ { X Jerry } } }\nf"
} $nl
"let's have them come back." $nl
{ $unchecked-example
"{ { mouseo Jerry } { mouseo Nibbles } } facts
{ creatureo X } query ."
"{ H{ { X Tom } } H{ { X Jerry } } H{ { X Nibbles } } }"
} $nl
"Logic predicates that take different numbers of arguments are treated separately. The previously used " { $snippet "cato" } " took one argument. Let's define " { $snippet "cato" } " that takes two arguments." $nl
{ $unchecked-example
"SYMBOLS: big small a-big-cat a-small-cat ;
{ cato big a-big-cat } fact
{ cato small a-small-cat } fact
{ cato X } query .
{ cato X Y } query .
{ creatureo X } query ."
"{ H{ { X Tom } } }\n{ H{ { X big } { Y a-big-cat } } H{ { X small } { Y a-small-cat } } }\n{ H{ { X Tom } } H{ { X Jerry } } H{ { X Nibbles } }"
"If you need to identify a logic predicate that has a different " { $strong "arity" } ", that is numbers of arguments, express it with a slash and an arity number. For example, " { $snippet "cato" } " with arity 1 is " { $snippet "cato/1" } ", " { $snippet "cato" } " with arity 2 is " { $snippet "cato/2" } ". But, note that " { $snippet "logic" } " does not recognize these names." $nl
{ $link clear-pred } " will clear all definitions of any arity. If you only want to remove the definition of a certain arity, you should use " { $link retract-all } " with logic variables." $nl
"Within these backquotes are comparisons, calculations, and assignments (to be precise, " { $strong "unifications" } "). " { $snippet "logic" } " has a mechanism to call Factor code to do these things. Here are some example." $nl
{ $code "{ N2_is_N_-_1 N2 N } [ dup N of 1 - N2 unify ] callback" }
{ $code "{ F_is_F2_*_N F F2 N } [ dup [ F2 of ] [ N of ] bi * F unify ] callback" } $nl
"Use " { $link callback } " to set the quotation to be called. Such quotations take an " { $strong "environment" } " which holds the binding of logic variables, and returns " { $link t } " or " { $link f } " as a result of execution. To retrieve the values of logic variables in the environment, use " { $link of } " or " { $link at } "." $nl
"The word " { $link unify } " unifies the two following the environment in that environment." $nl
"Now we can rewrite the definition of factorialo to use them." $nl
"There are the built-in logic predicates " { $link (<) } ", " { $link (>) } ", " { $link (>=) } ", and " { $link (=<) } " to compare numbers. There are also " { $link (==) } " and " { $link (\==) } " to test for equality and inequality of two arguments." $nl
"The word " { $link is } " takes a quotation and a logic variable to be unified. The quotation takes an environment and returns a value. And " { $link is } " returns the internal representation of the goal. " { $link is } " is intended to be used in a quotation. If there is a quotation in the definition of " { $link rule } ", " { $snippet "logic" } " uses the internal definition of the goal obtained by calling it." $nl
"Use the built-in logic predicate " { $link (=) } " for unification that does not require processing with a quotation. " { $link (\=) } " will be true when such a unification fails. Note that " { $link (\=) } " does not actually do the unification." $nl
{ $link varo } " takes a argument and is true if it is a logic variable with no value. On the other hand, " { $link nonvaro } " is true if its argument is not a logic variable or is a concrete logic variable." $nl
