Clojurians Log v2
meander
I am trying to pass patterns into a function that applies these using search but I am doing something wrong. Example which works when I hardcode the patterns into the function. I have troed unquoting the pattern inside apply-rule, but that makes no difference:
(def global-counter (java.util.concurrent.atomic.AtomicInteger. 0))
(defn next-id [] (.getAndIncrement global-counter))
(defn apply-rule [graph rule]
(let [[pattern out] rule]
(map vec
(partition
2
(flatten
(me/search
graph
(me/scan pattern)
out))))))
(let [g [[(next-id) (next-id)]]]
(apply-rule g '[[?x ?y] [[(next-id) ?y] [?y ?x]]]))
Sorry for taking so long to reply. I definitely don’t recommend doing this. But just wanted to reply with the eval version.
(def global-counter (java.util.concurrent.atomic.AtomicInteger. 0))
(defn next-id [] (.getAndIncrement global-counter))
(defn apply-rule [graph rule]
(let [[pattern out] rule]
(map vec
(partition
2
(flatten
(eval
`(m/search
~graph
(m/scan ~pattern)
~out)))))))Right now this isn’t possible because meander works by compiling patterns. This makes these dynamic things not work. We are actively working on an interpreter though https://github.com/noprompt/meander/pull/155 If you are doing this for some other reason than wanting dynamic patterns, we can definitely help with that too if you explain a bit more about your motivation. In the example you gave it is hard for me to tell if you really need things to be dynamic.
I was looking to pass the patterns to have a concise way to let the user play around with different patterns.
Yeah right now the only way do things dynamically like that would be to eval stuff.
How would I use eval to achieve this? I am confused.
On my phone sadly. Can post later tonight. But if you are accepting user input, eval is not safe.
By user input, I meant just to let the user of the library pass quoted patterns into the function. Happy to wait for input.
@mac It sounds like you want interpretation which the PR @jimmy linked earlier will provide support once it is merged. I have been actively working on it and expect to have it merged soon. I have shared a couple of examples demonstrating it https://clojurians.slack.com/archives/CFFTD7R6Z/p1606244106396700 and https://clojurians.slack.com/archives/CFFTD7R6Z/p1606936033435400. I’m currently trying to round a few more rough edges and going as quickly as I can. I know this is a feature folks want (including myself) and it’s my number one priority right now.
OK, that's cool. I will use hard coded patterns for now.