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(defmodule Array
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(doc reduce "will reduce an array `xs` into a single value using a function `f` that takes the reduction thus far and the next value. The initial reduction value is `x`.
As an example, consider this definition of `sum` based on `reduce`:
```
(defn sum [x]
(reduce + 0 x))
```
It will sum the previous sum with each new value, starting at `0`.")
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(defn reduce [f x xs]
(let [total x]
(do
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(for [i 0 (length xs)]
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(set! total (~f total (nth xs i))))
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total)))
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(doc empty? "checks whether the array `a` is empty.")
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(defn empty? [a]
(= (Array.length a) 0))
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(doc any? "checks whether any of the elements in `a` match the function `f`.")
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(defn any? [f a]
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(let-do [res false]
(for [i 0 (length a)]
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(when (~f (nth a i))
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(do
(set! res true)
(break))))
res))
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(doc all? "checks whether all of the elements in `a` match the function `f`.")
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(defn all? [f a]
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(let-do [res true]
(for [i 0 (length a)]
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(when (not (~f (nth a i)))
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(do
(set! res false)
(break))))
res))
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(doc find "finds an element in `a` that matches the function `f` and wraps it in a `Just`.
If it doesn’ t find an element, `Nothing` will be returned.")
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(defn find [f a]
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(let-do [res (Maybe.Nothing)]
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(for [i 0 (length a)]
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(when (~f (nth a i))
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(do
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(set! res (Maybe.Just @(nth a i)))
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(break))))
res))
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(doc find-index "finds the index of the first element in `a` that matches the function `f` and wraps it in a `Just`.
If it doesn’ t find an index, `Nothing` will be returned.")
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(defn find-index [f a]
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(let-do [ret (Maybe.Nothing)]
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(for [i 0 (length a)]
(when (~f (nth a i))
(do
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(set! ret (Maybe.Just i))
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(break))))
ret))
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(doc unsafe-first "takes the first element of an array.
Generates a runtime error if the array is empty.")
(defn unsafe-first [a]
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@(Array.nth a 0))
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(doc first "takes the first element of an array and returns a `Just`.
Returns `Nothing` if the array is empty.")
(defn first [a]
(if (empty? a)
(Maybe.Nothing)
(Maybe.Just @(Array.nth a 0))))
(doc unsafe-last "takes the last element of an array.
Generates a runtime error if the array is empty.")
(defn unsafe-last [a]
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@(Array.nth a (Int.dec (Array.length a))))
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(doc last "takes the last element of an array and returns a `Just`.
Returns `Nothing` if the array is empty.")
(defn last [a]
(if (empty? a)
(Maybe.Nothing)
(Maybe.Just @(Array.nth a (Int.dec (Array.length a))))))
(doc = "compares two arrays.")
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(defn = [a b]
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(if (/= (length a) (length b))
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false
(let-do [eq true]
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(for [i 0 (length a)]
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(when (/= @(nth a i) @(nth b i))
(do
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(set! eq false)
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(break))))
eq)))
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(doc = "compares two arrays and inverts the result.")
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(defn /= [a b]
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(not (= (the (Ref (Array a)) a) b)))
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(doc maximum "gets the maximum in an array (elements must support `<` and `zero`)and wraps it in a `Just`.
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If the array is empty, returns `Nothing`")
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(defn maximum [xs]
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(let-do [result (first xs)
n (length xs)
res (Maybe.from @&result (zero))]
(for [i 0 n]
(let [x @(nth xs i)]
(when (< &res &x)
(do
(set! result (Maybe.Just x))
(set! res x)))))
result))
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(doc minimum "gets the minimum in an array (elements must support `>` and `zero`) and wraps it in a `Just`.
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If the array is empty, returns `Nothing`")
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(defn minimum [xs]
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(let-do [result (first xs)
n (length xs)
res (Maybe.from @&result (zero))]
(for [i 0 n]
(let [x @(nth xs i)]
(when (> &res &x)
(do
(set! res x)
(set! result (Maybe.Just x))))))
result))
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(doc sum "sums an array (elements must support `+` and `zero`).")
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(defn sum [xs]
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(Array.reduce &(fn [x y] (+ x @y)) (zero) xs))
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(doc subarray "gets a subarray from `start-index` to `end-index`.")
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(defn subarray [xs start-index end-index]
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(let-do [result []]
(for [i start-index end-index]
(set! result (push-back result @(nth xs i))))
result))
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(doc prefix-array "gets a prefix array to `end-index`.")
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(defn prefix-array [xs end-index]
(subarray xs 0 end-index))
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(doc suffix-array "gets a suffix array from `start-index`.")
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(defn suffix-array [xs start-index]
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(subarray xs start-index (length xs)))
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(doc reverse "reverses an array.")
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(defn reverse [a]
(let-do [i 0
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j (Int.dec (length &a))]
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(while (Int.< i j)
(let-do [tmp @(nth &a i)]
(aset! &a i @(nth &a j))
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(set! i (Int.inc i))
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(aset! &a j tmp)
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(set! j (Int.dec j))))
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a))
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(doc index-of "gets the index of element `e` in an array.")
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(defn index-of [a e]
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(let-do [idx (Maybe.Nothing)]
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(for [i 0 (length a)]
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(when (= (nth a i) e)
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(do
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(set! idx (Maybe.Just i))
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(break))))
idx))
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(doc element-count "counts the occurrences of element `e` in an array.")
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(defn element-count [a e]
(let-do [c 0]
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(for [i 0 (length a)]
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(when (= e (nth a i)) (set! c (Int.inc c))))
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c))
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(doc predicate-count "counts the number of elements satisfying the predicate function `pred` in an array.")
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(defn predicate-count [a pred]
(let-do [c 0]
(for [i 0 (length a)]
(when (~pred (nth a i))
(set! c (Int.inc c))))
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c))
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(doc aupdate "transmutes (i.e. updates) the element at index `i` of an array `a` using the function `f`.")
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(defn aupdate [a i f]
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(let [new-value (~f (nth &a i))]
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(aset a i new-value)))
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(doc aupdate! "transmutes (i.e. updates) the element at index `i` of an array `a` using the function `f` in place.")
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(defn aupdate! [a i f]
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(aset! a i (~f (nth a i))))
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(doc swap "swaps the indices `i` and `j` of an array `a`.")
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(defn swap [a i j]
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(let [x @(nth &a i)
y @(nth &a j)]
(aset (aset a i y) j x)))
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(doc swap! "swaps the indices `i` and `j` of an array `a` in place.")
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(defn swap! [a i j]
(let-do [x @(nth a i)
y @(nth a j)]
(aset! a i y)
(aset! a j x)))
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; cannot use for, because we want also be able to go downwards
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(doc range "creates an array from `start` to `end` with `step` between them (the elements must support `<`, `<=`, `>=`, and `to-int`).")
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(defn range [start end step]
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(let-do [x (allocate (Int.inc (Int.abs (to-int (/ (- end start) step)))))
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e start
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i 0
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op (if (< start end) <= >=)]
(while (op e end)
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(do
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(aset! &x i e)
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(set! i (Int.inc i))
(set! e (+ e step))))
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x))
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(doc repeat "repeats the function `f` `n` times and stores the results in an array.")
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(defn repeat [n f]
(let-do [a (allocate n)]
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(for [i 0 n] (aset-uninitialized! &a i (~f)))
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a))
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(doc repeat-indexed "repeats function `f` `n `times and stores the results in an array.
This is similar to [`repeat`](#repeat), but the function `f` will be supplied with the index of the element.")
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(defn repeat-indexed [n f]
(let-do [a (allocate n)]
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(for [i 0 n] (aset-uninitialized! &a i (f i)))
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a))
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(doc replicate "repeats element `e` `n` times and stores the results in an array.")
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(defn replicate [n e]
(let-do [a (allocate n)]
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(for [i 0 n] (aset-uninitialized! &a i @e))
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a))
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(doc copy-map "maps over an array `a` using the function `f`.
This function copies the array. If you don’ t want that, use [`endo-map`](#endo-map).")
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(defn copy-map [f a]
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(let-do [na (allocate (length a))]
(for [i 0 (length a)]
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(aset-uninitialized! &na i (~f (nth a i))))
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na))
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(doc zip "maps over two arrays using a function `f` that takes two arguments. It will produces a new array with the length of the shorter input.
The trailing elements of the longer array will be discarded.")
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(defn zip [f a b]
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(let-do [l (Int.min (length a) (length b))
na (allocate l)]
(for [i 0 l]
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(aset-uninitialized! &na i (~f (nth a i) (nth b i))))
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na))
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(doc sum-length "returns the sum of lengths from a nested array `xs`.")
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(defn sum-length [xs]
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(let-do [sum 0
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lxs (Array.length xs)]
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(for [i 0 lxs]
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(set! sum (+ sum (Array.length (Array.nth xs i)))))
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sum))
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(doc zero "returns the empty array.")
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(defn zero [] [])
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(doc concat "returns a new array which is the concatenation of the provided nested array `xs`.")
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(defn concat [xs]
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;; This is using a StringBuilder pattern to only perform one allocation and
;; to only copy each of the incoming Array(s) once.
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;; This currently performs wasted Array.length calls, as we call it for each
;; Array once here and once in sum-length.
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(let-do [j 0
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lxs (Array.length xs)
result (Array.allocate (sum-length xs))]
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(for [i 0 lxs]
(let-do [arr (Array.nth xs i)
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len (Array.length arr)]
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(for [k 0 len]
(aset-uninitialized! &result (+ j k) @(Array.nth arr k)))
(set! j (+ j len))))
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result))
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(doc enumerated "creates a new array of `Pair`s where the first position is the index and the second position is the element from the original array `xs`.")
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(defn enumerated [xs]
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(zip &Pair.init-from-refs
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&(range 0 (length xs) 1) ;; Inefficient, creates a temporary array.
xs))
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(doc remove "removes all occurrences of the element `el` in the array `arr`, in place.")
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(defn remove [el arr]
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(endo-filter &(fn [x] (not (= el x)))
arr))
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(doc remove-nth "removes element at index `idx` from the array `arr`.")
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(defn remove-nth [i arr]
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(do
;;(assert (<= 0 i))
;;(assert (< i (Array.length &arr)))
(for [j i (Int.dec (Array.length &arr))]
(aset! &arr j @(nth &arr (inc j))))
(pop-back arr)))
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(doc copy-filter "filters the elements in an array.
It will create a copy. If you want to avoid that, consider using [`endo-filter`](#endo-filter) instead.")
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(defn copy-filter [f a] (endo-filter f @a))
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)