Clojurians Log v2

yeah. i'm a big believer in "stop forcing devs to play compiler/computer in their heads"

Given the code below -

(m/search [{:farm ""}
           {:farm "a"}
           {:farm ""}]
  (m/scan {:farm _ :as ?row})
  (assoc ?row :farm "b"))

Here are two other ways you could write this:

(m/rewrite [{:farm ""}
            {:farm "a"}
            {:farm ""}]
  [{:farm _ & !rest} ...]
  [{:farm "b" & !rest} ...])


(m/rewrites [{:farm ""}
             {:farm "a"}
             {:farm ""}]
   (m/scan {:farm _ & ?rest})
  {:farm "b" & ?rest})

(m/search [[{:a 1} {:c 3}] [{:b 2} {:d 5}]]
  (m/scan [{:as ?row}])
  (assoc ?row :z 1))

(m/rewrites [[{:a 1} {:c 3}] [{:b 2} {:d 5}]]
  (m/scan (m/scan {& ?rest}))
  {:z 2 & ?rest})

@jimmy thanks, let me try to wrap my head around rewrite/rewrites, when do I use it, it looks very similar to match/search ?

So both rewrite and rewrites use m/subst on the right hand side. If you think about pattern matching as deconstructing values, substitution is the constructing of values. Basically it extends many of meanders features for creating things as well as matching on them. To make it concrete, instead of rewrites I could have just said:

(m/search [{:farm ""}
             {:farm "a"}
             {:farm ""}]
   (m/scan {:farm _ & ?rest})
  (m/subst
    {:farm "b" & ?rest}))

cool thanks

(m/rewrite [[{:a 1} {:c 3}] [{:b 2} {:d 5}]]
  [(m/cata !xs) ...]
  [!xs ...]

  {:as ?it}
  {:z 2 & ?it})
;; =>
[[{:a 1, :z 2} {:c 3, :z 2}] [{:b 2, :z 2} {:d 5, :z 2}]]

@murtaza52 ☝️

One rule to rewrite vectors (recursively rewriting their members), and one to rewrite maps.

Meander has some built-in resistance to complex movements, in particular update “in place”. If you find yourself trying to figure out how to do a transform in one fell swoop, break it up in to more focused rules and use m/cata to drive the traversal, etc.

Hey folks, I’ve pushed up the some work I’ve been doing to make it possible to dynamically create pattern search interpreters. https://github.com/noprompt/meander/pull/128

It’s not quite ready to merge. In the spirit of including the community to the extent I can, I’m welcoming feedback both here and on the PR.

It’ll at least be another couple weeks before this will get merged. In the mean time I plan to address the regression recently pointed out and smooth out any rough edges I see.

Questions are welcome. I know some have mentioned a desire to understand how the semantics are implemented in code and I said that I think an interpreter can help with that. If there’s still confusion, I’m happy to walk through it.