140 lines
4.0 KiB
Markdown
140 lines
4.0 KiB
Markdown
# Language List
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Welcome to Language List on Exercism's Elixir Track.
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If you need help running the tests or submitting your code, check out `HELP.md`.
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If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)
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## Introduction
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## Lists
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Lists are built-in to the Elixir language. They are considered a basic type, denoted by square brackets. Lists may be empty or hold any number of items of any type. For example:
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```elixir
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empty_list = []
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one_item_list = [1]
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two_item_list = [1, 2]
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multiple_type_list = [1, :pi, 3.14, "four"]
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```
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Elixir implements lists as a linked list, where each node stores two values: the first item and another list with all the remaining items. The first item in the list is referred to as the _head_ and the remaining list of items is called the _tail_. We can use this notation in code:
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```elixir
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# [1] represented in [head | tail] notation
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[1 | []]
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# [1, 2, 3] represented in [head | tail] notation
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[1 | [2 | [3 | []]]]
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```
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We can use _`[head | tail]`_ notation to prepend elements to a list:
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```elixir
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# Suppose
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list = [2, 1]
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[3, 2, 1] == [3 | list]
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# => true
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```
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There are several functions in the `Kernel` module for working with lists, as well as the whole `List` module.
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```elixir
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# Check if 1 is a member of the list
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1 in [1, 2, 3, 4]
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# => true
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```
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## Instructions
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In this exercise you need to implement some functions to manipulate a list of programming languages.
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## 1. Define a function to return an empty language list
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Define the `new/0` function that takes no arguments and returns an empty list.
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```elixir
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LanguageList.new()
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# => []
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```
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## 2. Define a function to add a language to the list
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Define the `add/2` function that takes 2 arguments (a _language list_ and a string literal of a _language_). It should return the resulting list with the new language prepended to the given list.
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```elixir
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language_list = LanguageList.new()
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# => []
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language_list = LanguageList.add(language_list, "Clojure")
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# => ["Clojure"]
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language_list = LanguageList.add(language_list, "Haskell")
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# => ["Haskell", "Clojure"]
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```
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## 3. Define a function to remove a language from the list
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Define the `remove/1` function that takes 1 argument (a _language list_). It should return the list without the first item. Assume the list will always have at least one item.
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```elixir
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language_list = LanguageList.new()
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# => []
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language_list = LanguageList.add(language_list, "Clojure")
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# => ["Clojure"]
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language_list = LanguageList.add(language_list, "Haskell")
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# => ["Haskell", "Clojure"]
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language_list = LanguageList.remove(language_list)
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# => ["Clojure"]
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```
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## 4. Define a function to return the first item in the list
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Define the `first/1` function that takes 1 argument (a _language list_). It should return the first language in the list. Assume the list will always have at least one item.
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```elixir
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language_list = LanguageList.new()
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# => []
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language_list = LanguageList.add(language_list, "Elm")
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# => ["Elm"]
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language_list = LanguageList.add(language_list, "Prolog")
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# => ["Prolog", "Elm"]
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LanguageList.first(language_list)
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# => "Prolog"
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```
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## 5. Define a function to return how many languages are in the list
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Define the `count/1` function that takes 1 argument (a _language list_). It should return the number of languages in the list.
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```elixir
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language_list = LanguageList.new()
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# => []
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language_list = LanguageList.add(language_list, "Elm")
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# => ["Elm"]
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language_list = LanguageList.add(language_list, "Prolog")
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# => ["Prolog", "Elm"]
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LanguageList.count(language_list)
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# => 2
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```
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## 6. Define a function to determine if the list includes a functional language
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Define the `functional_list?/1` function which takes 1 argument (a _language list_). It should return a boolean value. It should return true if _"Elixir"_ is one of the languages in the list.
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```elixir
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language_list = LanguageList.new()
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# => []
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language_list = LanguageList.add(language_list, "Elixir")
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# => ["Elixir"]
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LanguageList.functional_list?(language_list)
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# => true
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```
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## Source
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### Created by
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- @neenjaw
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### Contributed to by
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- @fireproofsocks |