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list-ops: create exercise (#376)
* WIP: list-ops: create exercise * list-ops: rework for v3 directory structure - add dot files - add blurb about "library exercise" * list-ops: uses namerefs that require bash 4.3 * Fix GHA PR script: accurately identify files that need testing
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‎.github/scripts/pr‎

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# From that, extract the list of exercise directories, and
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# test there.
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minorVer=$(IFS="."; echo "${BASH_VERSINFO[*]:0:2}")
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if [[ $minorVer < "4.3" ]]; then
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echo "[Failure] This script requires bash version 4.3+" >&2
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exit 1
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if ((BASH_VERSINFO[0] < 4)); then
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echo "[Failure] This script requires bash version 4+" >&2
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exit 4
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fi
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shopt -s extglob
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declare -A seen=()
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declare -a dirs
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status=0
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for file; do
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dir=$(dirname "$file")
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# this file is NOT under the exercises dir: nothing to test
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[[ $dir == */exercises/* ]] || continue
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if [[ ! -v seen["$dir"] ]]; then
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seen["$dir"]=1
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bin/validate_one_exercise "$dir" || status=1
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if [[ $file =~ ^exercises/(practice|concept)/[^/]+ ]]; then
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dir=${BASH_REMATCH[0]}
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if [[ -z ${seen[$dir]} ]]; then
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bin/validate_one_exercise "$dir" || status=1
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seen["$dir"]=yes
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fi
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fi
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done
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‎config.json‎

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"strings",
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"transforming"
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]
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},
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{
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"slug": "list-ops",
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"name": "List Operations",
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"uuid": "3ce05308-2637-4f85-8e88-51739778605c",
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"prerequisites": [],
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"difficulty": 7,
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"topics": [
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"algorithms",
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"arrays",
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"conditionals",
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"filtering",
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"loops",
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"variables"
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]
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}
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]
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},

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

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# Library of Functions
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This is the first exercise we've seen where the solution we're writing
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is not a "main" script. We're writing a library to be "source"d into
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other scripts that will invoke our functions.
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## Bash namerefs
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This exercise requires the use of `nameref` variables. This requires a bash
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version of at least 4.0. If you're using the default bash on MacOS, you'll
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need to install another version: see [Installing Bash](https://exercism.io/tracks/bash/installation)
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Namerefs are a way to pass a variable to a function _by reference_. That
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way, the variable can be modified in the function and the updated value is
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available in the calling scope. Here's an example:
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```bash
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prependElements() {
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local -n __array=$1
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shift
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__array=( "$@" "${__array[@]}" )
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}
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my_array=( a b c )
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echo "before: ${my_array[*]}" # => before: a b c
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prependElements my_array d e f
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echo "after: ${my_array[*]}" # => after: d e f a b c
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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
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`reduce` are very common. Implement a series of basic list operations,
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without using existing functions.
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The precise number and names of the operations to be implemented will be
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track dependent to avoid conflicts with existing names, but the general
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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 using `function(accumulator, item)`*);
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* `foldr` (*given a function, a list, and an initial accumulator, fold (reduce) each item into the accumulator from the right using `function(item, accumulator)`*);
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* `reverse` (*given a list, return a list with all the original items, but in reversed order*);

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

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{
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"authors": [],
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"files": {
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"solution": ["list_ops.sh"],
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"test": ["list_ops_test.sh"],
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"example": [".meta/example.sh"]
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}
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}

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

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#!/usr/bin/env bash
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bash_version=$((10 * BASH_VERSINFO[0] + BASH_VERSINFO[1]))
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if (( bash_version < 43 )); then
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echo "This library requires at least bash version 4.3" >&2
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return 4
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fi
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# Due to inherent bash limitations around word splitting and globbing,
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# functions that are intended to *return a list* are instead required to
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# receive a nameref parameter, the name of an array variable that will be
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# populated in the list function.
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# See the filter, map and reverse functions.
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# Also note that nameref parameters cannot have the same name as the
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# name of the variable in the calling scope.
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# Append some elements to the given list.
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list::append () {
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local -n __list1=$1
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shift
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__list1+=( "$@" )
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}
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# Return only the list elements that pass the given function.
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list::filter () {
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local funcname=$1
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local -n __list=$2
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local -n __result=$3
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for element in "${__list[@]}"; do
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$funcname "$element" && __result+=("$element")
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done
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}
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# Transform the list elements, using the given function,
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# into a new list.
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list::map () {
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local funcname=$1
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local -n __list=$2
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local -n __result=$3
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for element in "${__list[@]}"; do
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__result+=( "$($funcname "$element")" )
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done
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}
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# Left-fold the list using the function and the initial value.
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list::foldl () {
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local funcname=$1 acc=$2
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local -n __list=$3
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for element in "${__list[@]}"; do
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acc=$( $funcname "$acc" "$element" )
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done
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echo "$acc"
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}
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# Right-fold the list using the function and the initial value.
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list::foldr () {
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local funcname=$1 acc=$2
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local -n __list=$3
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for (( i = ${#__list[@]} - 1; i >=0; i-- )); do
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acc=$( $funcname "${__list[i]}" "$acc" )
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done
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echo "$acc"
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}
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# Return the list reversed
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list::reverse () {
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local -n __list=$1
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local -n __result=$2
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local -i size=${#__list[@]}
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for (( i = 0; i < size; i++ )); do
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__result[i]=${__list[-1 - i]}
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done
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}

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

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[canonical-tests]
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# empty lists
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"485b9452-bf94-40f7-a3db-c3cf4850066a" = true
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# list to empty list
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"2c894696-b609-4569-b149-8672134d340a" = true
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# empty list to list
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"e842efed-3bf6-4295-b371-4d67a4fdf19c" = true
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# non-empty lists
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"71dcf5eb-73ae-4a0e-b744-a52ee387922f" = true
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# empty list
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"28444355-201b-4af2-a2f6-5550227bde21" = false
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# list of lists
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"331451c1-9573-42a1-9869-2d06e3b389a9" = false
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# list of nested lists
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"d6ecd72c-197f-40c3-89a4-aa1f45827e09" = false
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# empty list
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"0524fba8-3e0f-4531-ad2b-f7a43da86a16" = true
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# non-empty list
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"88494bd5-f520-4edb-8631-88e415b62d24" = true
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# empty list
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"1cf0b92d-8d96-41d5-9c21-7b3c37cb6aad" = false
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# non-empty list
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"d7b8d2d9-2d16-44c4-9a19-6e5f237cb71e" = false
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# empty list
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"c0bc8962-30e2-4bec-9ae4-668b8ecd75aa" = true
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# non-empty list
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"11e71a95-e78b-4909-b8e4-60cdcaec0e91" = true
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# empty list
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"613b20b7-1873-4070-a3a6-70ae5f50d7cc" = false
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# direction independent function applied to non-empty list
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"e56df3eb-9405-416a-b13a-aabb4c3b5194" = false
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# direction dependent function applied to non-empty list
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"d2cf5644-aee1-4dfc-9b88-06896676fe27" = false
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# empty list
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"36549237-f765-4a4c-bfd9-5d3a8f7b07d2" = true
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# direction independent function applied to non-empty list
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"7a626a3c-03ec-42bc-9840-53f280e13067" = true
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# direction dependent function applied to non-empty list
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"d7fcad99-e88e-40e1-a539-4c519681f390" = true
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# empty list
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"aeb576b9-118e-4a57-a451-db49fac20fdc" = false
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# direction independent function applied to non-empty list
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"c4b64e58-313e-4c47-9c68-7764964efb8e" = false
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# direction dependent function applied to non-empty list
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"be396a53-c074-4db3-8dd6-f7ed003cce7c" = false
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# empty list
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"17214edb-20ba-42fc-bda8-000a5ab525b0" = true
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# direction independent function applied to non-empty list
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"e1c64db7-9253-4a3d-a7c4-5273b9e2a1bd" = true
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# direction dependent function applied to non-empty list
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"8066003b-f2ff-437e-9103-66e6df474844" = true
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# empty list
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"94231515-050e-4841-943d-d4488ab4ee30" = true
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# non-empty list
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"fcc03d1e-42e0-4712-b689-d54ad761f360" = true
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# list of lists is not flattened
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"40872990-b5b8-4cb8-9085-d91fc0d05d26" = false

‎exercises/practice/list-ops/list_ops.sh‎

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#!/usr/bin/env bash
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if [[ "${BASH_SOURCE[0]}" == "$0" ]]; then
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echo "This library of functions should be sourced into another script" >&2
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exit 4
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fi
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bash_version=$((10 * BASH_VERSINFO[0] + BASH_VERSINFO[1]))
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if (( bash_version < 43 )); then
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echo "This library requires at least bash version 4.3" >&2
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return 4
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fi
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# Due to inherent bash limitations around word splitting and globbing,
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# functions that are intended to *return a list* are instead required to
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# receive a nameref parameter, the name of an array variable that will be
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# populated in the list function.
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# See the filter, map and reverse functions.
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# Also note that nameref parameters cannot have the same name as the
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# name of the variable in the calling scope.
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# Append some elements to the given list.
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list::append () {
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echo "Implement me" >&2
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return 1
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}
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# Return only the list elements that pass the given function.
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list::filter () {
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echo "Implement me" >&2
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return 1
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}
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# Transform the list elements, using the given function,
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# into a new list.
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list::map () {
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echo "Implement me" >&2
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return 1
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}
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# Left-fold the list using the function and the initial value.
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list::foldl () {
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echo "Implement me" >&2
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return 1
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}
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# Right-fold the list using the function and the initial value.
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list::foldr () {
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echo "Implement me" >&2
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return 1
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}
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# Return the list reversed
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list::reverse () {
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echo "Implement me" >&2
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return 1
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}

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