I couldn't understand differences between IFn and fn.
Could you give examples too?
Please provide differences between those functions:
(fn? x)
(ifn? x)
they behave like same.
Clojure docs describes the difference quite clearly:
(fn? x)
Returns true if x implements Fn, i.e. is an object created via fn.
(ifn? x)
Returns true if x implements IFn. Note that many data structures
(e.g. sets and maps) implement IFn
You can test it:
(fn? (fn [] nil)) ;; => true
(fn? #{}) ;; => false
(fn? {}) ;; => false
(fn? []) ;; => false
(fn? :a) ;; => false
(fn? 'a) ;; => false
(ifn? (fn [] nil)) ;; => true
(ifn? #{}) ;; => true
(ifn? {}) ;; => true
(ifn? []) ;; => true
(ifn? :a) ;; => true
(ifn? 'a) ;; => true
In other words fn? says if its argument is an object which is just and only a function (created with (fn ...)), ifn? says if an object is a thing which can be called like a function (even if it wasn't created with (fn ...)).
Related
I need to match two kinds of tuples and produce maps from them.
Both have a keyword and a string. One can have a third item (a language code).
[<key> <value>] ~> {:type <key> :value <value>}
[<key> <value> <lang>] ~> {:type <key> :value <value> :lang <lang>}
I only need to match those which keyword is either :foo or :bar and decided that I would use clojure.core.match:
(ns so.example
(:require
[clojure.core.match :refer [match]]))
(defn example-1 [ast]
(let [l10n-key #{:foo :bar}]
(match ast
[(k :guard l10n-key) v lang] {:type k :value v :lang lang}
[(k :guard l10n-key) v] {:type k :value v})))
(example-1 [:foo 10])
;=> {:type :foo, :value 10}
(example-1 [:bar 20 "en"])
;=> {:type :bar, :value 20, :lang "en"}
That works but I wanted to reuse the matching pattern :guard l10n-key in different clauses. So I thought I could use some syntax quoting and unquote splicing:
(defn example-2 [ast]
(let [l10n-key-match [:guard #{:foo :bar}]]
(match ast
[`(k ~#l10n-key-match) v lang] {:type k :value v :lang lang}
[`(k ~#l10n-key-match) v] {:type k :value v})))
However the defn expression crashes with:
Unexpected error (AssertionError) macroexpanding match at (form-init11111096422056977084.clj:3:5).
Invalid list syntax (clojure.core/concat (clojure.core/list (quote so.example/k)) l10n-key-match) in (clojure.core/seq (clojure.core/concat (clojure.core/list (quote so.example/k)) l10n-key-match)). Valid syntax: [[:default :guard] [:or :default] [:default :only] [:default :seq] [:default :when] [:default :as] [:default :<<] [:default :clojure.core.match/vector]]
What am I doing wrong?
Isn't this what spec, that already ships with Clojure, does? You would define your pattern like
(ns playground.catspec
(:require [clojure.spec.alpha :as spec]))
(spec/def ::type #{:foo :bar})
(spec/def ::value number?)
(spec/def ::lang #{"en" "sv" "fr"})
(spec/def ::key-value-lang (spec/cat :type ::type
:value ::value
:lang (spec/? ::lang)))
We use spec/def to define a spec, spec/cat to concatenate specs and spec/? for a spec that is optional.
Then we use conform to parse the tuple:
(spec/conform ::key-value-lang [:foo 10])
;; => {:type :foo, :value 10}
(spec/conform ::key-value-lang [:bar 20 "en"])
;; => {:type :bar, :value 20, :lang "en"}
(spec/conform ::key-value-lang [:bar 119 "fr"])
;; => {:type :bar, :value 119, :lang "fr"}
(spec/conform ::key-value-lang [119 :foo])
;; => :clojure.spec.alpha/invalid
(spec/conform ::key-value-lang [:bar 119 "uj"])
;; => :clojure.spec.alpha/invalid
(spec/conform ::key-value-lang [:bar])
;; => :clojure.spec.alpha/invalid
(spec/conform ::key-value-lang [:bar 119 "fr" :asdfasdf])
;; => :clojure.spec.alpha/invalid
(spec/conform ::key-value-lang {:a 1 :b 4})
;; => :clojure.spec.alpha/invalid
Doesn't solve the problem with clojure.core.match, but you don't really need it for something this simple:
(ns tst.demo.core
(:use tupelo.core tupelo.test))
(dotest
(let [data [[:foo 10]
[:bar 20 "en"]
[:fizz 10]
[:buzz 20 "en"]]
keep-tags #{:foo :bar}
data-keep (filterv #(contains? keep-tags (first %)) data)
result (forv [tuple data-keep]
(zipmap [:type :value :lang] tuple))]
(is= result [{:type :foo, :value 10}
{:type :bar, :value 20, :lang "en"}])))
You may also be interested in these helper functions:
tupelo.core/matches? A nicer interface to clojure.core.match
tupelo.core/submatch?
tupelo.core/wild-match?
tupelo.core/wild-submatch?
Consider the following spec for a text or a link layer port number:
(require '[clojure.spec.alpha :as spec])
(spec/def ::text (spec/and string? not-empty))
(spec/valid? ::text "a") ; => true
(spec/valid? ::text "") ; => false
(spec/def ::port (spec/and pos-int? (partial > 65535)))
(spec/valid? ::port 4) ; => true
(spec/valid? ::port 0) ; => false
(spec/def ::text-or-port (spec/or ::text ::port))
(spec/valid? ::text-or-port 5) ; => true
(spec/valid? ::text-or-port "hi") ; => false
For some reason it only accepts port-numbers and not text, why would that be?
The key to understanding this problem can be found in in the documentation and using spec/conform.
(spec/conform ::text-or-port 5)
; => [:user/text 5]
The problem is that clojure.spec.alpha/or has an API which is dissimmilar to clojure.core/or which given two arguments returns the first truthy one:
(#(or (string? %) (integer? %)) 5) ; => true
(#(or (string? %) (integer? %)) "") ; => true
(#(or (string? %) (integer? %)) :a) ; => false
Rather it takes pairs of labels and specs/predicates. And since even namespaced keywords are accepted as labels the ::text-or-port spec given in the OP matched only that which passed the requirements for ::port and gave it the label ::text. Below is a correct spec for that which we want to match:
(spec/def ::text-or-port (spec/or :text ::text
:port ::port))
(spec/valid? ::text-or-port "hi") ; => true
(spec/valid? ::text-or-port 10) ; => true
I have developed Om/React components, but I feel really uncomfortable not being able to drive my development with unit tests. I have tried to setup my clojurescript project to run unit tests on those components, and so far reached the point where I am able to write unit tests and instantiate my components. What I am missing is the ability to ensure my components properly react to some events, e.g. onChange so that I can simulate user inputs.
Here is my test code:
(defn simulate-click-event
"From https://github.com/levand/domina/blob/master/test/cljs/domina/test.cljs"
[el]
(let [document (.-document js/window)]
(cond
(.-click el) (.click el)
(.-createEvent document) (let [e (.createEvent document "MouseEvents")]
(.initMouseEvent e "click" true true
js/window 0 0 0 0 0
false false false false 0 nil)
(.dispatchEvent el e))
:default (throw "Unable to simulate click event"))))
(defn simulate-change-event
"From https://github.com/levand/domina/blob/master/test/cljs/domina/test.cljs"
[el]
(let [document (.-document js/window)]
(cond
(.-onChange el) (do (print "firing on change on " el) (.onChange el))
(.-createEvent document) (let [e (.createEvent document "HTMLEvents")]
(print "firing " e " on change on " (.-id el))
(.initEvent e "change" true true)
(.dispatchEvent el e))
:default (throw "Unable to simulate change event"))))
(def sink
"contains a channel that receives messages along with notification type"
(chan))
;; see http://yobriefca.se/blog/2014/06/04/publish-and-subscribe-with-core-dot-asyncs-pub-and-sub/
(def source
(pub sink #(:topic %)))
(defn change-field!
[id value]
(let [el (sel1 (keyword (str "#" id)))]
(dommy/set-value! el value)
(simulate-change-event el)
))
(deftest ^:async password-confirmation
(testing "do not submit if passwords are not equal"
(let [subscription (chan)]
(sub source :user-registration subscription)
(om/root
(partial u/registration-view source sink)
nil
{:target (sel1 :#view)})
(go
(let [m (<! subscription)]
(is (= :error (:state m)))
(done)
))
(change-field! "userRequestedEmail" "foo#bar.com")
(change-field! "userRequestedPassword" "secret")
(change-field! "confirmPassword" "nosecret")
(simulate-click-event (sel1 :#submitRegistration))
)))
This test runs but fails because the change-field! function does not actually change the state of the component. Here is (part of) the code of the component (forgive duplication...):
(defn registration-view
"Registration form for users.
Submitting form triggers a request to server"
[source sink _ owner]
(reify
om/IInitState
(init-state [_]
{:userRequestedEmail ""
:userRequestedPassword ""
:confirmPassword ""}
)
om/IRenderState
(render-state
[this state]
(dom/fieldset
nil
(dom/legend nil "User Registration")
(dom/div #js { :className "pure-control-group" }
(dom/label #js { :for "userRequestedEmail" } "EMail")
(dom/input #js { :id "userRequestedEmail" :type "text" :placeholder "Enter an e-mail"
:value (:userRequestedEmail state)
:onChange #(om/set-state! owner :userRequestedEmail (.. % -target -value))}))
(dom/div #js { :className "pure-control-group" }
(dom/label #js { :for "userRequestedPassword" } "Password")
(dom/input #js { :id "userRequestedPassword" :type "password" :placeholder "Enter password"
:value (:userRequestedPassword state)
:onChange #(om/set-state! owner :userRequestedPassword (.. % -target -value))}))
(dom/div #js { :className "pure-control-group" }
(dom/label #js { :for "confirmPassword" } "")
(dom/input #js { :id "confirmPassword" :type "password" :placeholder "Confirm password"
:value (:confirmPassword state)
:onChange #(om/set-state! owner :confirmPassword (.. % -target -value))}))
(dom/button #js {:type "submit"
:id "submitRegistration"
:className "pure-button pure-button-primary"
:onClick #(submit-registration state sink)}
"Register")))))
What I can see by putting traces in the tests is that the state of the component is not updated when I trigger the change event, although it is correctly triggered. I suspect this has to do with the way Om/React works, wrapping DOM components, but not sure how to deal with this.
You can mock events in your components using ReactTestUtils from the react libraries.
I'm using mocha and doing something like this to test change events:
var comp = ReactTestUtils.renderIntoDocument(<Component />);
var changingElement = ReactTestUtils.findRenderedDOMComponentWithClass(comp, 'el-class');
it ('calls myChangeMethod on change', function() {
ReactTestUtils.Simulate.change(changingElement);
assert(comp.myChangeEventMethod.called, true);
}
I want the following outcome:
"1" -> true
"0" -> false
nil -> nil
How can this function be improved?
#(when-not (nil? %) (if % "1" "0"))
Your requirement translates directly into a map and maps are also callable as functions in Clojure, so {1 true, 0 false} is the function you want.
({1 true, 0 false} 1) ;;=> true
({1 true, 0 false} 0) ;;=> false
({1 true, 0 false} nil) ;;=> nil
Please look at the following code:
(def data {:color ["R", "B", "G"] :name "Hello" :up "down"})
(defn collapse-vector-kvp [k v]
(map #(hash-map k %) v))
(defn collapse-map [m]
(map #(let
[x %]
(if (vector? (val x))
(collapse-vector-kvp (key x) (val x))
(hash-map (key x) (val x))
)) m))
(collapse-map data)
=> ({:name "Hello"} ({:color "R"} {:color "B"} {:color "G"}) {:up "down"})
What I would like to do is create a single list, rather than have the 'color' entries be in a list within the list. Is this easily achievable?
user=> (def data2 '({:name "Hello"} ({:color "R"} {:color "B"} {:color "G"}) {:up "down"}))
#'user/data2
user=> (flatten data2)
({:name "Hello"} {:color "R"} {:color "B"} {:color "G"} {:up "down"})
Another version of collapse-map:
(defn collapse-map [m]
(let [sep-m (group-by (comp vector? val) m)]
(concat (map (fn [[k v]] {k v})
(sep-m false))
(apply concat (map (fn [[k v]]
(collapse-vector-kvp k v))
(sep-m true))))))
(def test-data {:color ["R" "B" "G"]
:name "Hello"
:k ["v1" "v2" "v3"]
:up "down"})
(collapse-map test-data)
=> ({:name "Hello"}
{:up "down"}
{:color "R"}
{:color "B"}
{:color "G"}
{:k "v1"}
{:k "v2"}
{:k "v3"})