matchete

Yet another pattern matching library for Clojure(Script).

Using

(require '[matchete.core :as m])

;; `match?` function returns true or false to indicate if the data matches the pattern
(m/match? '{:foo ?foo} {:foo 1}) ;; => true
(m/match? '{:bar ?bar} {:foo 1}) ;; => false

;; `matches` function returns lazy sequence with collected bindings
;; empty seq indicates not matched data
(m/matches '{:foo ?foo} {:foo 1}) ;; => '({?foo 1})
(m/matches '{:bar ?bar} {:foo 1}) ;; => '()

;; `matcher` function precompiles pattern into a function
(let [matcher (m/matcher '{:foo ?foo})]
  (matcher {:foo 1})) ;; => '({?foo 1})

Match data using data as a pattern

(m/match? 42 42) ;; => true
(m/match? "42" "24") ;; => false

;; sequences
(m/match? [1 2 3] [1 2 3]) ;; => true
(m/match? '(1 2 3) [1 2 3]) ;; => true

(m/match? [1 2 3] [1 2 3 4]) ;; => false because pattern expects exactly 3 elements

;; to override this behaviour tail destructuring pattern can be used
(m/match? [1 2 3 & _] [1 2 3 4]) ;; => true, `_` is a placeholder here that will match to any provided data

;; hash-maps
(m/match? {:id 123 :name "Alise"} {:id 123 :name "Alise" :lastname "Cooper"}) ;; => true
(m/match? {:id 123 :name "Alise"} {:id 123 :lastname "Cooper"}) ;; => false because `:name` key is missing

Extract data

There are three types of special symbols that can be used in a pattern:

• data bindings - symbols starts with '?'
• memo bindings - symbols starts with '!'
• named rule - symbols starts with '$'

Data Binding

(m/matches '?user {:id 1 :name "Bob"}) ;; => '({?user {:id 1 :name "Bob"}})
(m/matches '{:id ?user-id :name ?user-name}
            {:id 1        :name "Bob"}) ;; => '({?user-id 1 ?user-name "Bob"})

(m/matches '[1 ?two 3 & [?four & _]]
            [1 2    3    4       5 6]) ;; => '({?two 2 ?four 4})

(m/matches '{:vector [_       {:id ?id}]}
            {:vector [{:id 1} {:id 2}]}) ;; => '({?id 2})

data bindings can be used as a hash-map keys

(m/matches '{?key ?value}
            {:foo "foo"
             :bar "bar"}) ;; => '({?key :foo ?value "foo"} {?key :bar ?value "bar"})

(m/matches '{?x "foo"
             ?y "bar"}
            {:key-1 "foo"
             :key-2 "foo"
             :key-3 "bar"}) ;; => '({?x :key-1 ?y :key-3} {?x :key-2 ?y :key-3})

Memo Binding

Collect data into a vector. Order of appearence is not guaranteed.

(m/matches '[{:id !ids} {:id !ids} {:id !ids}]
            [{:id 1}    {:id 2}    {:id 3}]) ;; => '({!ids [1 2 3]})

Control sequences

cat combinator

Each pattern will be applied to the same data combine data bindings into one result. Patterns can extend the result or add more sofisticated restrictions.

(m/matches '(cat {:id ?id :name ?name} ?user)
            {:id 1
             :name "Alise"
             :lastname "Cooper"}) ;; => '({?id 1 ?name "Alise" ?user {:id 1 :name "Alise" :lastname "Cooper"}})

alt combinator

Patterns combined by alt will be applied to the same data as long as one of them will match and the matches from that pattern will be the result of matching.

(m/matches '(alt {:id ?id} {"id" ?id} {:userId ?id})
            {:id 1}        ;; => '({?id 1})
            ;; {"id" 2}    ;; => '({?id 2})
            ;; {:userId 3} ;; => '({?id 3})
            )

scan

Expects one pattern wich will be applied to each item of sequence or hash-map (item will be in the form of tuple: [key, value]).

(m/matches '{:foo (scan [?id ?name])}
            {:foo [[1 "Alise"] [::empty] [3 "Bob"]]}) ;; => '({?id 1 ?name "Alise"} {?id 3 ?name "Bob"})'

scan-indexed

Expects two patterns:

1. index matcher (index in sequences and key in hash-maps)
2. value matcher

(m/matches '(scan-indexed !path (scan-indexed !path (scan-indexed !path ?node)))
            [{:id 1
              :user {:name "Alise"
                     :role :admin}
              :actions [{:type :login}]}])
;; => '({!path [0 :user :name] ?node "Alise"}
;;      {!path [0 :user :role] ?node :admin}
;;      {!path [0 :actions 0]  ?node {:type :login}})

Named rule

(m/matches '(def-rule $children (scan-indexed !path (alt $children ?leaf)))
            [{:id 1
              :user {:name "Alise"
                     :role :admin}
              :actions [{:type :login}]}])
;; => '({!path [0 :id]              ?leaf 1}
;;      {!path [0 :user :name]      ?leaf "Alise"}
;;      {!path [0 :user :role]      ?leaf :admin}
;;      {!path [0 :actions 0 :type] ?leaf :login})

;; rules can be precompiled
(let [rules {'$children (m/matcher '(scan-indexed !path (alt $children ?leaf)))}]
  (m/matches '$children rules
             [{:id 1
               :user {:name "Alise"
                      :role :admin}
               :actions [{:type :login}]}]))
;; => '({!path [0 :id]              ?leaf 1}
;;      {!path [0 :user :name]      ?leaf "Alise"}
;;      {!path [0 :user :role]      ?leaf :admin}
;;      {!path [0 :actions 0 :type] ?leaf :login})