docs: add "Common Patterns" to cookbook

[ikrima]

Update: merged feedback below

Adding noprompt feedback from slack here for posterity/to incorporate:

---

Gotcha. There are two approaches you could apply here. The first one uses a helper to construct the xseg:

(defn make-xseg [val]
  (m/rewrite val
    (m/re #"@.*" ?val)
    {:kind :seg-attr :val ?val}

    (m/re #"[^@].*" ?val)
    {:kind :seg-chld :val ?val}

    ?val
    {:kind :unknown :val ?val}))

(m/rewrite ["oppas" "obj1" "@attr1" "@attr2" "obj2"]
  [(m/re #"obj|oppas|dc" ?ns) . !segs ...]
  {:ns (m/keyword ?ns)
   :xsegs [(m/app make-xseg !segs) ...]})
;; =>
{:ns :oppas,
 :xsegs
 [{:kind :seg-chld, :val "obj1"}
  {:kind :seg-attr, :val "@attr1"}
  {:kind :seg-attr, :val "@attr2"}
  {:kind :seg-chld, :val "obj2"}]}

The second uses m/cata on the left or right side:

;; Left side
(m/rewrite ["oppas" "obj1" "@attr1" "@attr2" "obj2"]
  [(m/re #"obj|oppas|dc" ?ns) . (m/cata !segs) ...]
  {:ns (m/keyword ?ns)
   :xsegs [!segs ...]}

  (m/re #"@.*" ?val)
  {:kind :seg-attr :val ?val}

  (m/re #"[^@].*" ?val)
  {:kind :seg-chld :val ?val}

  ?val
  {:kind :unknown :val ?val})

;; Right side
(m/rewrite ["oppas" "obj1" "@attr1" "@attr2" "obj2"]
  [(m/re #"obj|oppas|dc" ?ns) . !segs ...]
  {:ns (m/keyword ?ns)
   :xsegs [(m/cata !segs) ...]}

  (m/re #"@.*" ?val)
  {:kind :seg-attr :val ?val}

  (m/re #"[^@].*" ?val)
  {:kind :seg-chld :val ?val}

  ?val
  {:kind :unknown :val ?val})

(m/rewrite ["oppas" "obj1" "@attr1" "@attr2" "obj2"]
  [(m/re #"obj|oppas|dc" ?ns) . !segs ...]
  {:ns (m/keyword ?ns)
   :xsegs [(m/cata ($EXAMPLE !segs)) ...]}

  ($EXAMPLE (m/re #"@.*" ?val))
  {:kind :seg-attr :val ?val}

  ($EXAMPLE (m/re #"[^@].*" ?val))

  {:kind :seg-chld :val ?val}

  ($EXAMPLE ?val)
  {:kind :unknown :val ?val})
;; =>
{:ns :oppas,
 :xsegs
 [{:kind :seg-chld, :val "obj1"}
  {:kind :seg-attr, :val "@attr1"}
  {:kind :seg-attr, :val "@attr2"}
  {:kind :seg-chld, :val "obj2"}]}

[noprompt]

This looks great. Thanks!