Clojurians Log v2

Why would the below fail with Execution error (IllegalArgumentException) at meander.interpreter.epsilon/match-clause-factory$fn$fn$fn (epsilon.cljc:490). Key must be integer :

(let [q ['?y '?x]
      f (mi/searcher
         q ['?x])]
  (f [:x 1]))

@mac

(defn project
  "Helper which extracts the values of vars (keys) out a map in the
  order they are given.
  Example:
    (let [f (mi/finder '[?x ?y] (project '[?y ?x ?y]))]
      (f [1 2]))
    ;; => [2 1 2]"
  [vars]
  (fn [bindings] (mapv bindings vars)))

(let [q '[?y ?x]
      f (mi/searcher
         q (project ['?x]))]
  (f [:x 1]))
;; => [1]

(defn debug
  [vars]
  (fn [bindings]
    {:vars vars
     :bindings bindings}))

(let [q '[?y ?x]
      f (mi/finder
         q (debug '?x))]
  (f [:x 1]))
;; =>
;; {:vars ?x,
;;  :bindings {:meander.interpreter.epsilon/cata #function
;;             [meander.interpreter.epsilon/match-system-factory/fn--23289/f--23292] ,
;;             ?y :x,
;;             ?x 1}}

I suspect that if the data being thrown into the function returned by the intrepreter is a vector, it unfolds to something similar

(let [date [:x 1])
      l ['?y '?x]
      r '?x]
  (let [idx (.indexOf l r)]
    (.get data idx)))

I guess this is a bug, because if idx is nil, the rest of the function should not be continued.

If you want to do something a bit more complicated then you should create a function that takes a query and that returns a function that takes a hasmap with the bindings.

(let [q '[?y ?x]
      f (mi/finder
         q {:a '?x})]
  (f [:x 1]))
;; => nil

(let [q '[?y ?x]
      f (mi/finder
         q ((fn [x] (fn [bindings] {:a (get bindings x)})) '?x))]
  (f [:x 1]))
;; => {:a 1}

Although IMHO does not make sense, it is better to build the collection that we need after obtaining the value

(let [q '[?y ?x]
      f (mi/finder
         q '?x)]
  {:a (f [:x 1])})

Will take a look at this later today is someone else doesn't get to it first.

Yeah, the interpreter stuff likely has rough edges. Please also report these on Github too if you don’t mind. 🙂