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Add ListOps exercise
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‎config.json‎

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"practices": [],
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"prerequisites": [],
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"difficulty": 2
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},
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{
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"slug": "list-ops",
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"name": "List Ops",
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"uuid": "56f36086-96a8-4941-8c46-b563f02e5b09",
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"practices": [],
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"prerequisites": [],
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"difficulty": 5
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}
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]
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},

‎exercises/practice/list-ops/.docs/instructions.md‎

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# Instructions
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Implement basic list operations.
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In functional languages list operations like `length`, `map`, and `reduce` are very common.
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Implement a series of basic list operations, without using existing functions.
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The precise number and names of the operations to be implemented will be track dependent to avoid conflicts with existing names, but the general operations you will implement include:
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- `append` (_given two lists, add all items in the second list to the end of the first list_);
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- `concatenate` (_given a series of lists, combine all items in all lists into one flattened list_);
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- `filter` (_given a predicate and a list, return the list of all items for which `predicate(item)` is True_);
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- `length` (_given a list, return the total number of items within it_);
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- `map` (_given a function and a list, return the list of the results of applying `function(item)` on all items_);
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- `foldl` (_given a function, a list, and initial accumulator, fold (reduce) each item into the accumulator from the left_);
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- `foldr` (_given a function, a list, and an initial accumulator, fold (reduce) each item into the accumulator from the right_);
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- `reverse` (_given a list, return a list with all the original items, but in reversed order_).
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Note, the ordering in which arguments are passed to the fold functions (`foldl`, `foldr`) is significant.

‎exercises/practice/list-ops/.meta/config.json‎

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{
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"authors": ["homersimpsons"],
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"files": {
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"solution": [
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"ListOps.php"
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],
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"test": [
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"ListOpsTest.php"
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],
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"example": [
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".meta/example.php"
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]
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},
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"blurb": "Implement basic list operations."
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}

‎exercises/practice/list-ops/.meta/example.php‎

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<?php
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/*
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* By adding type hints and enabling strict type checking, code can become
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* easier to read, self-documenting and reduce the number of potential bugs.
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* By default, type declarations are non-strict, which means they will attempt
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* to change the original type to match the type specified by the
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* type-declaration.
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*
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* In other words, if you pass a string to a function requiring a float,
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* it will attempt to convert the string value to a float.
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*
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* To enable strict mode, a single declare directive must be placed at the top
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* of the file.
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* This means that the strictness of typing is configured on a per-file basis.
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* This directive not only affects the type declarations of parameters, but also
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* a function's return type.
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*
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* For more info review the Concept on strict type checking in the PHP track
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* <link>.
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*
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* To disable strict typing, comment out the directive below.
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*/
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declare(strict_types=1);
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class ListOps
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{
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public static function append(array $list1, array $list2): array
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{
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foreach ($list2 as $el) {
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$list1[] = $el;
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}
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return $list1;
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}
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public static function concat(array $list1, array ...$listn): array
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{
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foreach ($listn as $list) {
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$list1 = self::append($list1, $list);
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}
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return $list1;
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}
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public static function filter(callable $predicate, array $list): array
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{
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$result = [];
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foreach ($list as $el) {
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if ($predicate($el)) {
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$result[] = $el;
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}
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}
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return $result;
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}
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public static function length(array $list): int
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{
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$count = 0;
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foreach ($list as $_el) {
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$count++;
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}
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return $count;
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}
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public static function map(callable $function, array $list): array
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{
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$result = [];
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foreach ($list as $el) {
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$result[] = $function($el);
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}
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return $result;
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}
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public static function foldl(callable $function, array $list, $accumulator)
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{
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foreach ($list as $el) {
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$accumulator = $function($accumulator, $el);
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}
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return $accumulator;
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}
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public static function foldr(callable $function, array $list, $accumulator)
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{
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while (self::length($list) > 0) {
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$el = array_pop($list);
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$accumulator = $function($accumulator, $el);
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}
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return $accumulator;
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}
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public static function reverse(array $list): array
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{
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$result = [];
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while (self::length($list) > 0) {
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$result[] = array_pop($list);
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}
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return $result;
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}
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}

‎exercises/practice/list-ops/.meta/tests.toml‎

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[485b9452-bf94-40f7-a3db-c3cf4850066a]
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description = "append entries to a list and return the new list -> empty lists"
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[2c894696-b609-4569-b149-8672134d340a]
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description = "append entries to a list and return the new list -> list to empty list"
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[e842efed-3bf6-4295-b371-4d67a4fdf19c]
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description = "append entries to a list and return the new list -> empty list to list"
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[71dcf5eb-73ae-4a0e-b744-a52ee387922f]
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description = "append entries to a list and return the new list -> non-empty lists"
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[28444355-201b-4af2-a2f6-5550227bde21]
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description = "concatenate a list of lists -> empty list"
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[331451c1-9573-42a1-9869-2d06e3b389a9]
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description = "concatenate a list of lists -> list of lists"
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[d6ecd72c-197f-40c3-89a4-aa1f45827e09]
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description = "concatenate a list of lists -> list of nested lists"
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[0524fba8-3e0f-4531-ad2b-f7a43da86a16]
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description = "filter list returning only values that satisfy the filter function -> empty list"
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[88494bd5-f520-4edb-8631-88e415b62d24]
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description = "filter list returning only values that satisfy the filter function -> non-empty list"
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[1cf0b92d-8d96-41d5-9c21-7b3c37cb6aad]
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description = "returns the length of a list -> empty list"
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[d7b8d2d9-2d16-44c4-9a19-6e5f237cb71e]
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description = "returns the length of a list -> non-empty list"
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[c0bc8962-30e2-4bec-9ae4-668b8ecd75aa]
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description = "return a list of elements whose values equal the list value transformed by the mapping function -> empty list"
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[11e71a95-e78b-4909-b8e4-60cdcaec0e91]
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description = "return a list of elements whose values equal the list value transformed by the mapping function -> non-empty list"
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[613b20b7-1873-4070-a3a6-70ae5f50d7cc]
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description = "folds (reduces) the given list from the left with a function -> empty list"
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include = false
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[e56df3eb-9405-416a-b13a-aabb4c3b5194]
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description = "folds (reduces) the given list from the left with a function -> direction independent function applied to non-empty list"
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include = false
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[d2cf5644-aee1-4dfc-9b88-06896676fe27]
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description = "folds (reduces) the given list from the left with a function -> direction dependent function applied to non-empty list"
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include = false
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[36549237-f765-4a4c-bfd9-5d3a8f7b07d2]
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description = "folds (reduces) the given list from the left with a function -> empty list"
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reimplements = "613b20b7-1873-4070-a3a6-70ae5f50d7cc"
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[7a626a3c-03ec-42bc-9840-53f280e13067]
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description = "folds (reduces) the given list from the left with a function -> direction independent function applied to non-empty list"
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reimplements = "e56df3eb-9405-416a-b13a-aabb4c3b5194"
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[d7fcad99-e88e-40e1-a539-4c519681f390]
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description = "folds (reduces) the given list from the left with a function -> direction dependent function applied to non-empty list"
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reimplements = "d2cf5644-aee1-4dfc-9b88-06896676fe27"
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[aeb576b9-118e-4a57-a451-db49fac20fdc]
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description = "folds (reduces) the given list from the right with a function -> empty list"
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include = false
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[c4b64e58-313e-4c47-9c68-7764964efb8e]
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description = "folds (reduces) the given list from the right with a function -> direction independent function applied to non-empty list"
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include = false
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[be396a53-c074-4db3-8dd6-f7ed003cce7c]
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description = "folds (reduces) the given list from the right with a function -> direction dependent function applied to non-empty list"
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include = false
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[17214edb-20ba-42fc-bda8-000a5ab525b0]
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description = "folds (reduces) the given list from the right with a function -> empty list"
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reimplements = "aeb576b9-118e-4a57-a451-db49fac20fdc"
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[e1c64db7-9253-4a3d-a7c4-5273b9e2a1bd]
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description = "folds (reduces) the given list from the right with a function -> direction independent function applied to non-empty list"
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reimplements = "c4b64e58-313e-4c47-9c68-7764964efb8e"
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[8066003b-f2ff-437e-9103-66e6df474844]
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description = "folds (reduces) the given list from the right with a function -> direction dependent function applied to non-empty list"
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reimplements = "be396a53-c074-4db3-8dd6-f7ed003cce7c"
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[94231515-050e-4841-943d-d4488ab4ee30]
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description = "reverse the elements of the list -> empty list"
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[fcc03d1e-42e0-4712-b689-d54ad761f360]
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description = "reverse the elements of the list -> non-empty list"
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[40872990-b5b8-4cb8-9085-d91fc0d05d26]
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description = "reverse the elements of the list -> list of lists is not flattened"

‎exercises/practice/list-ops/ListOps.php‎

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<?php
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/*
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* By adding type hints and enabling strict type checking, code can become
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* easier to read, self-documenting and reduce the number of potential bugs.
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* By default, type declarations are non-strict, which means they will attempt
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* to change the original type to match the type specified by the
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* type-declaration.
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*
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* In other words, if you pass a string to a function requiring a float,
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* it will attempt to convert the string value to a float.
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*
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* To enable strict mode, a single declare directive must be placed at the top
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* of the file.
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* This means that the strictness of typing is configured on a per-file basis.
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* This directive not only affects the type declarations of parameters, but also
17+
* a function's return type.
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*
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* For more info review the Concept on strict type checking in the PHP track
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* <link>.
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*
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* To disable strict typing, comment out the directive below.
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*/
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declare(strict_types=1);
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class ListOps
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{
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public static function append(array $list1, array $list2): array
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{
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throw new \BadMethodCallException("Implement the append function");
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}
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public static function concat(array $list1, array ...$listn): array
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{
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throw new \BadMethodCallException("Implement the concat function");
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}
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public static function filter(callable $predicate, array $list): array
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{
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throw new \BadMethodCallException("Implement the filter function");
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}
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public static function length(array $list): int
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{
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throw new \BadMethodCallException("Implement the length function");
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}
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public static function map(callable $function, array $list): array
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{
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throw new \BadMethodCallException("Implement the map function");
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}
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public static function foldl(callable $function, array $list, $accumulator)
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{
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throw new \BadMethodCallException("Implement the foldl function");
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}
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public static function foldr(callable $function, array $list, $accumulator)
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{
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throw new \BadMethodCallException("Implement the foldr function");
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}
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public static function reverse(array $list): array
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{
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throw new \BadMethodCallException("Implement the reverse function");
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}
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}

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