Clojurians Log v2

Hi all, just reading through the meander docs, and wondering if anyone could shed light on what the difference is between the scan and [ ...] formulations? For example:

{:user
 {:name ?name
  :favorite-foods (m/scan {:name ?food})}}

{:user
 {:name ?name
  :favorite-foods [{:name !food} ...]}}

(m/scan p1 ,,, pn) is similar to

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

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

(m/match #{{:id 1} {:id 2}} #{{:id 1}} :yes)

(m/match #{{:id 1} {:id 2}} #{{:id ?id}} :yes)

Match requires things to be unambigious. But that isn’t the case here. So you can use m/search to get all the answers, or m/find to get the first.

(m/search #{{:id 1} {:id 2}} 
  #{{:id ?id}}
  [?id :yes])

;; =>
([2 :yes] [1 :yes])

To explain the difference a bit more concretely, scan lets there be gaps in the data, where as ... requires all elements to make the pattern. You can see that in the difference between these two.

(m/search [1 2 3 4 5 6]
  (m/scan (m/pred even? ?xs))
  ?xs)

;; => [2 4 6]

(m/find [1 2 3 4 5 6]
  [(m/pred even? !xs) ...]
  !xs)

;; => nil

thanks for the answer @jimmy, that's exactly what I needed! Amazing library!

I'm observing a weird behaviour that I think could be a bug. I'm in a cljs file: if I do

(m/search example-2 a-pattern an-action)

(m/search workspace/example-2 a-pattern an-action)

Syntax error macroexpanding cljs.core/fn.
Call to cljs.core/fn did not conform to spec.
-- Spec failed --------------------

  ([workspace/example-2_T__] ...)
    ^^^^^^^^^^^^^^^^^^^^^^^

has extra input

or

should satisfy

  vector?

-- Relevant specs -------

:shadow.cljs.devtools.cljs-specs/param-list:
  (clojure.spec.alpha/and
   clojure.core/vector?
   (clojure.spec.alpha/cat
    :params
    (clojure.spec.alpha/* :shadow.cljs.devtools.cljs-specs/binding-form)
    :var-params
    (clojure.spec.alpha/?
     (clojure.spec.alpha/cat
      :ampersand
      #{'&}
      :var-form
      :shadow.cljs.devtools.cljs-specs/binding-form))))
:shadow.cljs.devtools.cljs-specs/params+body:
  (clojure.spec.alpha/cat
   :params
   :shadow.cljs.devtools.cljs-specs/param-list
   :body
   (clojure.spec.alpha/alt
    :prepost+body
    (clojure.spec.alpha/cat
     :prepost
     clojure.core/map?
     :body
     (clojure.spec.alpha/+ clojure.core/any?))
    :body
    (clojure.spec.alpha/* clojure.core/any?)))

Sounds like a bug. If you let bins workspace/example-2 to a local variable does it work? Can't look at this right now. But will try to recreate tonight.

yes, either a variable in the same file or a variable in a let binding works:

(let [example-2 ...]
  (m/search example-2 a-pattern an-action))

Cool should be an easy fix.

and of course this works too:

(let [example-2 workspace/example-2] ...)