Table of Contents
(rule clear-cart-on-command ; <-- rule name
{:group :action} ; <-- salience group (optional)
[[_ :clear-cart]] ; <-- tuple expression with ignored first slot
; and value slot omitted
[?item <- [_ :cart-item/product-id]] ; <-- expr. with fact binding (?item)
=> ; <-- separator
(retract! ?item)) ; <-- right-hand side / consequence(rule add-item-to-cart-when-not-in-cart-on-command
{:group :action}
[[_ :add-to-cart ?product-id]] ; <-- variable binding in value slot
[:not [_ :cart-item/product-id ?product-id]] ; <-- boolean operator
=>
(api/add-to-cart {:db/id (random-uuid) ; <-- entity map
:cart-item/product-id ?product-id
:cart-item/quantity 1}))Vector representation:
[[id :cart-item/product-id 123]
[id :cart-item/quantity 1]])Map representation:
{:db/id id
:cart-item/product-id 123
:cart-item/quantity 1}Record representation (internal):
[(->Tuple id :cart-item/product-id 123 1)
(->Tuple id :cart-item/quantity 1 2)]?<symbol-name>
- First reference: binds a value to the variable
- Subsequent references: variable contains the value
Example:
; ?e binds to eid of a fact with attribute :color, value "blue"
[[?e :color "blue"]]
; ?e has been assigned a value. Expression uses the value
; captured from the previous expression when finding a match
[[?e :shape "circle"]][[_ keyword? ?any]]
Ignores e or v slot within a tuple expression. May not be used to ignore an attribute.
[<variable> <- <expression>]
Binds result of expression to variable.
Usage:
[?my-color-fact <- [_ :color "blue"]][?all-color-facts <- (acc/all) :from [_ :color]] [(<- <variable> <special-form>)]
Binds a variable to the result of a special form
Usage:
(:require-macros [precept.dsl :refer [<- entity]])
...
[[?e :color "blue"]]
[(<- ?blue-entity (entity ?e)]][(<- <unbound-variable> (entity <bound-variable=eid>))]
Accumulates all facts for a given entity id.
(:require-macros [precept.dsl :refer [<- entity]])
...
[[?e :color "blue"]]
[(<- ?blue-entity (entity ?e)]][(<- <unbound-variable> (entities <bound-variable=[eids]>))]
Accumulates all facts from a collection of entity ids.
(:require-macros [precept.dsl :refer [<- entities]])
...
[?eids <- (acc/all :e) :from [_ :color "blue"]]
[(<- ?blue-entities (entities ?eids)]]Positionally match all or some of a fact's fields.
[any? keyword? any?]
[keyword?] | [_ keyword?]
[any? keyword?] | [_ keyword?]
[<unbound-variable> <- <tuple-expression | accumulator-expression>]
Binds a fact to a variable. Binds a list of facts if expression is an accumulator.
Example:
[?my-fact <- [_ :color "blue"]][:test <predicate>]
Test expressions may be used to specify an arbitrary predicate as part of the rule's condition.
Example:
[[_ :high-temp/yesterday ?x]]
[[_ :high-temp/today ?y]]
[[_ :high-temp/tomorrow ?z]]
[:test (> (max ?x ?y ?z) 100)]Arbitrary s-expressions predicates may be used in the value slot.
Examples:
[[?e :number (> 42 ?num)]](def magic-number 42)
(defn my-func [x]
(and (number? x)
(> (+ 1 x) magic-number)))
...
[[?e :number (my-func ?num)]][<variable> <- <accumulator-function> :from <tuple-expression>]
See precept.accumulators namespace for list of predefined accumulator functions.
Example:
[?names-of-colors <- (acc/all :v) :from [_ :color]][:or <expression> <expression> ...]
Logical or.
May nest or be nested within other boolean expressions.
[:and <expression> <expression> ...]
Logical and.
May nest or be nested within other boolean expressions.
Because expressions contain an implicit logical and, reserve for cases where a logical and must be explicit.
Usage:
[:or [:and [_ :color "blue"]
[_ :shape "circle"]]
[:and [_ :color "yellow"]
[_ :shape "triangle"]]][:not <expression>]
Logical not.
May nest or be nested within other boolean expressions.
Usage:
[[?e :shape "circle"]]
[:not [?e :color "blue"]][:not [:and [_ :color "blue"]
[_ :shape "circle"]]][:exists <expression>]
True if the wrapped expression has at least one match.
Usage:
[[?e :shape ?triangle]]
[:exists [?e :color "blue"]](insert! <entity-vector | entity-map | Tuple>)
Argument may be a collection of one supported type.
For use in the consequence block of a rule only.
Equivalent of insert logical. Inserts facts that exist so long as the conditions under which they were inserted are true.
(insert-unconditional! <entity-vector | entity-map | Tuple>)
Argument may be a collection of one supported type.
For use in the consequence block of a rule only.
Inserts facts that exist until they are manually removed.
(insert! <session> <entity-vector | entity-map | Tuple>)
For use outside of a consequence block.
Inserts facts that exist until they are manually removed.
Takes a session as first argument. Second argument may be a collection of one supported type.
(retract! <Tuple>)
Removes fact from session.
For use in the consequence block of a rule only.
Argument may be a collection of Tuple record instances. Requires fact instance to retract.
Example:
[?blue-fact <- [_ :color "blue"]]
=>
(retract! ?blue-fact)[?blue-facts <- (acc/all) :from [_ :color "blue"]]
=>
(retract! ?blue-facts)(retract <session> <Tuple>)
Removes fact from session.
For use outside of a consequence block.
Second argument may be a collection of Tuple record instances.
When :color is "blue":
[[_ :color "blue"]]Value slot can be anything.
Equality determined by Clojure's = function.
When a fact with attribute :color, bind its value to ?color:
[[_ :color ?color]]Creates variable ?color and binds it to the value in the value slot.
When a fact with attribute :color, bind the entire fact to ?my-fact:
[?my-fact <- [_ :color ?color]]?coloris still available as a bound value?my-factis returned as aTuplerecord instance
Obtains when an entity with the same eid has :color "blue" and :shape "circle".
[[?e :color "blue"]]
[[?e :shape "circle"]]Obtains when a :temperature/current fact and :temperature/record-high fact
have the same value.
[[_ :current-temperature ?v]]
[[_ :really-hot-temperature ?v]]Fact values may hold references to other facts.
[[_ :node/parent ?node-id]]
[[?node-id :node/name ?name]]