meander.epsilon — meander/epsilon 0.0.383

$ clj

($ pattern)

($ context-pattern pattern)

Pattern matching and substitution operator.

When used as a pattern matching operator will attempt match pattern against some value that is a subtree of the target of pattern matching. Optionally, context-pattern (should be a variable pattern) can be passed and will be applied against a function. This function accepts one argument and when invoked with some value x will return the original, root target updated with the x installed at the place where pattern matched successfully.

(match [:A 2]
  ($ (pred number? ?x))
  ?x)
;; => 2

(match [:A 2]
  ($ ?context (pred number? ?x))
  (?context 3))
;; => [:A 3]

$* clj

($* context pattern)

($* context pattern & patterns)

and clj

(and pattern & patterns)

Pattern matching operator which matches when pattern and, optionally, all of patterns match.

app clj

(app f pattern)

(app f pattern & patterns)

Pattern matching operator which applies pattern matching the result applying f to the current value being matched.

breadth-first-search clj/s macro

(breadth-first-search x & clauses)

Like search but traverses the search space in breadth first order.

cata clj

(cata pattern)

Pattern matching operator which causes pattern matching to recurse on the target of pattern matching. The result is then pattern matched with pattern.

(match [1 2 3]
  [(cata ?x) (cata ?y) (cata ?z)]
  [?x ?y ?z]

  3
  :three

  2
  :two

  1
  :one)
;; =>
[:one :two :three]

defsyntax clj/s macro

(defsyntax name doc-string? attr-map? [params*] prepost-map? body)

(defsyntax name doc-string? attr-map? ([params*] prepost-map? body) + attr-map?)

find clj/s macro

(find x match-pattern result & more-pattern-result-pairs)

Given some data x, returns a single result that satisfies match-clause which is the first solution explored in depth-first order.

Like search but returns only the first successful match.

gather clj

(gather pattern)

(gather pattern count-pattern)

Pattern matching operator that works in a similar manner to clojure.core/filter.

gather allows you to match a pattern over a seqable, ignoring any values that don't match.

(match [1 2 3 4]
  (gather (m/pred even? !xs))
  !xs)
  ;; =>
  [2 4]

gather also offers a two arity version that can be supplied a logic variable, memory variable, _ pattern, number, or an ellipsis that allows control over the repeat behavior of gather.

(match [:a :b :a :a :c]
  (gather :a ?count)
  ?count)
  ;; =>
  3

(match [:a :b :a :a :c]
  (gather :a ..4)
   true

   _
   false)
   ;; =>
   false

guard clj

(guard pred-expr)

Pattern matching operator which succeeds whenever pred-expr returns a truthy result. pred-expr is evaluated by Clojure.

keyword clj

(keyword name)

(keyword namespace name)

(keyword namespace name & rest)

Pattern matching and substitution operator.

When used as a pattern matching operator it will match a keyword with name and, optionally, namespace.

(match :foo/bar
  (keyword ?name)
  ?name)
;; => "bar"

(match :foo/bar
  (keyword ?namespace ?name)
  [?namespace ?name])
;; => ["foo" "bar"]

Additionally, the keyword itself can be pattern matched against the :as keyword argument.

(match :foo/bar
  (keyword _ _ :as ?keyword)
  ?keyword)
;; => :foo/bar

When used as a substutition operator it will create a keyword with name and, optionally, namespace e.g. it behaves the same as clojure.core/keyword in the context of normal substitution behavior.

(subst (keyword "foo" "bar"))
;; => :foo/bar

;; clojure.core/let
(let [!namespaces ["foo" "foo"]
      !names ["bar" "baz"]]
  (subst [(keyword !namespaces !names) ...]))
;; => [:foo/bar :foo/baz]

For substitution the :as keyword argument is ignored.

let clj

(let binding-patterns)

(let binding-patterns target-pattern)

match clj/s macro

(match x match-pattern result & more-pattern-result-pairs)

Given some data x, return the corresponding result if it matches match-pattern. Logic variables may exist in both the match-pattern and result, enabling the reshaping of data. match is the fundamental pattern matching operator.

Syntax

(match x
  pattern_1 expr_1
  ,,,
  pattern_n expr_n)

Attempts to pattern match x against one of patterns pattern_1 through pattern_n. If some pattern pattern_i matches successfully, expr_i will be executed. If none of the patterns match successfully an error will be thrown indicating the pattern match failed.

This operator restricts patterns which may have several possible solutions. For example, the pattern

#{?x ?y}

matches any set with at least two elements. However, with consideration to the property that Clojure sets are unordered, there are many possible ways we could bind values for ?x and ?y. Because there is no obvious way to know which solution to pick, patterns which have this property are illegal in the context of this operator. For operators which relax this restriction, see find and search.

match-syntax? clj

(match-syntax? env)

not clj

(not pattern)

Pattern matching operator which matches when pattern does not match.

number clj

(number)

(number pattern)

Pattern matching operator which matches a number?. Optionally pattern may be passed to further pattern match on the value.

or clj

(or pattern & patterns)

Pattern matching operator which matches when either pattern or, opitionally, one of patterns match.

pred clj

(pred p)

(pred p pattern)

(pred p pattern & patterns)

Pattern matching operator which successfully matches whenever the target of pattern matching applied to expr returns a truthy value.

(match 1
  (pred odd?)
  :okay)
;; => :okay

Optionally, additional patterns patterns may be passed in which case they will be treated as an and pattern against the target of pattern matching.

(match 1
  (pred odd? ?x)
  :okay)

is the same as

(match 1
  (and (pred odd?) ?x)
  :okay)

re clj

(re regex-pattern)

(re regex-pattern capture-pattern)

Pattern matching operator which matches strings which match the regular expression regex-pattern with re-matches. Optionally, a second argument capture-pattern can be passed which will be matched against the result of the underlying re-matches call.

(match "foo"
  (re #"...")
  true)
;; =>
true

(match "foo"
  (re #"(.)(.)(.)" [?0 ?1 ?2 ?3])
  [?0 ?1 ?2 ?3])
;; =>
["foo" "f" "o" "o"]

rewrite clj/s macro

(rewrite x match-pattern subst-pattern & more-pattern-pairs)

Given some data x, match a match-pattern and substitute with the subst-pattern.

Syntactic sugar for

 (find x
   p_1 (subst p_2)
   ,,,
   p_n-1 (subst p_n))

rewrites clj/s macro

(rewrites x & clauses)

scan clj

(scan & patterns)

Pattern matching operator which matches the seq of seqable? forms of the shape

(_ ... p1 ,,, pn . _ ...)

or vectors? of the form

[_ ... p1 ,,, pn . _ ...]

where the sequence p1 through pn is equal to patterns.

search clj/s macro

(search x match-pattern result & more-pattern-result-pairs)

Given some data x, searches for variable assignments that satisfy a match-pattern, and returns a user defined result which may use those variables. Returns a lazy sequence of expression values in depth-first order.

Like match but allows for patterns which may match x in more than one way.

Example

(search [1 2 3]
  [!xs ... !ys ...]
  {'!xs !xs, '!ys !ys})
;; =>
({!xs [], !ys [1 2 3]}
 {!xs [1], !ys [2 3]}
 {!xs [1 2], !ys [3]}
 {!xs [1 2 3], !ys []})

Note, if only the first value is needed, use find instead. The expression

(first (search x ,,,))

can be significantly slower than

(find x ,,,)

separated clj

(separated & patterns)

Pattern matching operator which matches the seq of seqable? forms of the shape

(_ ... p1 ,,, . _ ... pn . _ ...)

or vectors? of the form

[_ ... p1 ,,, . _ ... pn . _ ...]

where the sequence p1 through pn is equal to patterns.

seqable clj

(seqable & patterns)

Pattern matching operator which matches the seq of anything that is seqable? against

(p1 ,,, pn)

where the sequence p1 through pn is equal to patterns.

some clj

(some)

(some pattern)

Pattern matching operator which matches a non nil value. Optionally, pattern may be passed to further match on the value.

subst clj/s macro

(subst pattern)

Substitution operator, the inverse of pattern matching. Evaluates pattern in the Clojure environment.

subst-syntax? clj

(subst-syntax? env)

symbol clj

(symbol name)

(symbol namespace name)

(symbol namespace name & rest)

Pattern matching and substitution operator.

When used as a pattern matching operator it will match a symbol with name and, optionally, namespace.

(match 'foo/bar
  (symbol ?name)
  ?name)
;; => "bar"

(match :foo/bar
  (symbol ?namespace ?name)
  [?namespace ?name])
;; => ["foo" "bar"]

Additionally, the symbol itself can be pattern matched against the :as keyword argument.

(match 'foo/bar
  (symbol _ _ :as ?symbol)
  ?symbol)
;; => 'foo/bar

When used as a substutition operator it will create a symbol with name and, optionally, namespace e.g. it behaves the same as clojure.core/symbol in the context of normal substitution behavior.

(subst (symbol "foo" "bar"))
;; => 'foo/bar

;; clojure.core/let
(let [!namespaces ["foo" "foo"]
      !names ["bar" "baz"]]
  (subst [(symbol !namespaces !names) ...]))
;; => ['foo/bar 'foo/baz]

For substitution the :as keyword argument is ignored.

with clj

(with pattern-bindings body)

Pattern matching and substitution operator.

Syntax

(with [%pattern-name pattern ...]
  target-pattern)

Allows for patterns to be referenced by %pattern-name in target-pattern.

Example

(match [[1 2] [1 2]]
  (with [%x-y [?x ?y]]
    [%x-y %x-y])
  {:x ?x, :y ?y})
;; =>
{:x 1, :y 2}