84 lines
2.6 KiB
Markdown
84 lines
2.6 KiB
Markdown
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# List of Macros with Examples
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## Path Macros
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### declarepath
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`(declarepath name)`
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`(declarepath name params)`
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Declares a new symbol available to be defined as a path. If the path will require parameters, these must be specified here.
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See also [providepath](#providepath)
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```clojure
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=> (declarepath SECOND)
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=> (providepath SECOND [(srange 1 2) FIRST])
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=> (select-one SECOND (range 5))
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1
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=> (transform SECOND dec (range 5))
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(0 0 2 3 4)
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```
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### defcollector
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`(defcollector name params collect-val-impl)`
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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.
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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.
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An informative example is the actual implementation of `putval`, which follows.
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```clojure
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=> (defcollector putval [val]
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(collect-val [this structure]
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val))
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=> (transform [ALL (putval 3)] + (range 5))
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(3 4 5 6 7)
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```
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### defnav
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`(defnav name params select-impl transform-impl)`
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`(defnav name params transform-impl select-impl)`
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Canonically the first is used.
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Defines a navigator with given name and parameters. Note that `params` should be a vector,
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as would follow `fn`.
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`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`.
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`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.
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See also [nav](#nav)
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```clojure
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=> (defnav nth-elt [n]
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(select* [this structure next-fn] (next-fn (nth structure n)))
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(transform* [this structure next-fn]
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(let [structurev (vec structure)
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ret (next-fn (nth structure n))]
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(if (vector? structure)
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(assoc structurev n ret)
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(concat (take n structure) (list ret) (drop (inc n) structure))))))
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=> (select-one (nth-elt 0) (range 5))
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0
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=> (select-one (nth-elt 3) (range 5))
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3
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=> (select-one (nth-elt 3) (range 0 10 2))
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6
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=> (transform (nth-elt 1) inc (range 5))
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(0 2 2 3 4)
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=> (transform (nth-elt 1) inc (vec (range 5)))
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[0 2 2 3 4]
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```
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### nav
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`(nav params select-impl transform-impl)`
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`(nav params transform-impl select-impl)`
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Returns an "anonymous navigator." See [defnav](#defnav).
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