specter-wiki/List-of-Macros.md

List of Macros with Examples

Path Macros

declarepath

(declarepath name) (declarepath name params)

Declares a new symbol available to be defined as a path. If the path will require parameters, these must be specified here.

See also providepath

=> (declarepath SECOND)
=> (providepath SECOND [(srange 1 2) FIRST])
=> (select-one SECOND (range 5))
1
=> (transform SECOND dec (range 5))
(0 0 2 3 4)

defcollector

(defcollector name params collect-val-impl)

Defines a collector with the given name and parameters. Collectors are navigators which add a value to the list of collected values and do not change the current structure.

Note that params should be a vector, as would follow fn. collect-val-impl must be of the form (collect-val [this structure] body). It should return the value to be collected.

An informative example is the actual implementation of putval, which follows.

=> (defcollector putval [val]
     (collect-val [this structure]
       val))
=> (transform [ALL (putval 3)] + (range 5))
(3 4 5 6 7)

defnav

(defnav name params select-impl transform-impl) (defnav name params transform-impl select-impl)

Canonically the first is used.

Defines a navigator with given name and parameters. Note that params should be a vector, as would follow fn.

select-impl must be of the form (select* [this structure next-fn] body). It should return the result of calling next-fn on whatever transformation the navigator applies to structure.

transform-impl must be of the form (transform* [this structure next-fn] body). It should find the result of calling nextfn on whatever transformation the navigator applies to structure. Then it should return the result of reconstructing the original structure with the results of the nextfn call.

See also nav

=> (defnav nth-elt [n] 
     (select* [this structure next-fn] (next-fn (nth structure n)))
     (transform* [this structure next-fn] 
       (let [structurev (vec structure) 
             ret (next-fn (nth structure n))] 
         (if (vector? structure) 
           (assoc structurev n ret)
           (concat (take n structure) (list ret) (drop (inc n) structure))))))
=> (select-one (nth-elt 0) (range 5))
0
=> (select-one (nth-elt 3) (range 5))
3
=> (select-one (nth-elt 3) (range 0 10 2))
6
=> (transform (nth-elt 1) inc (range 5))
(0 2 2 3 4)
=> (transform (nth-elt 1) inc (vec (range 5)))
[0 2 2 3 4]

nav

(nav params select-impl transform-impl) (nav params transform-impl select-impl)

Returns an "anonymous navigator." See defnav.