Initial upload

elixir/dna-encoding/.exercism/config.json

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+{
+  "authors": [
+    "neenjaw"
+  ],
+  "contributors": [
+    "angelikatyborska",
+    "NobbZ"
+  ],
+  "files": {
+    "solution": [
+      "lib/dna.ex"
+    ],
+    "test": [
+      "test/dna_test.exs"
+    ],
+    "exemplar": [
+      ".meta/exemplar.ex"
+    ]
+  },
+  "language_versions": ">=1.10",
+  "blurb": "Learn about bitstrings and tail call recursion by encoding DNA sequences as binary data."
+}

elixir/dna-encoding/.exercism/metadata.json

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+{"track":"elixir","exercise":"dna-encoding","id":"b36d8706517343e99bd8187edf2b3be6","url":"https://exercism.org/tracks/elixir/exercises/dna-encoding","handle":"halfdan","is_requester":true,"auto_approve":false}

elixir/dna-encoding/.formatter.exs

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+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

elixir/dna-encoding/.gitignore

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+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+bitstrings-*.tar
+

elixir/dna-encoding/HELP.md

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+# Help
+
+## Running the tests
+
+From the terminal, change to the base directory of the exercise then execute the tests with:
+
+```bash
+$ mix test
+```
+
+This will execute the test file found in the `test` subfolder -- a file ending in `_test.exs`
+
+Documentation:
+
+* [`mix test` - Elixir's test execution tool](https://hexdocs.pm/mix/Mix.Tasks.Test.html)
+* [`ExUnit` - Elixir's unit test library](https://hexdocs.pm/ex_unit/ExUnit.html)
+
+## Pending tests
+
+In test suites of practice exercises, all but the first test have been tagged to be skipped.
+
+Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.
+
+For example:
+
+```elixir
+# @tag :pending
+test "shouting" do
+  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
+end
+```
+
+If you wish to run all tests at once, you can include all skipped test by using the `--include` flag on the `mix test` command:
+
+```bash
+$ mix test --include pending
+```
+
+Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the file `test/test_helper.exs`.
+
+```elixir
+# ExUnit.configure(exclude: :pending, trace: true)
+```
+
+## Useful `mix test` options
+
+* `test/<FILE>.exs:LINENUM` - runs only a single test, the test from `<FILE>.exs` whose definition is on line `LINENUM`
+* `--failed` - runs only tests that failed the last time they ran
+* `--max-failures` - the suite stops evaluating tests when this number of test failures
+is reached
+* `--seed 0` - disables randomization so the tests in a single file will always be ran
+in the same order they were defined in
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit lib/dna.ex` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Elixir track's documentation](https://exercism.org/docs/tracks/elixir)
+- [Exercism's support channel on gitter](https://gitter.im/exercism/support)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+If you're stuck on something, it may help to look at some of the [available resources](https://exercism.org/docs/tracks/elixir/resources) out there where answers might be found.
+If you can't find what you're looking for in the documentation, feel free to ask help in the Exercism's BEAM [gitter channel](https://gitter.im/exercism/xerlang).

elixir/dna-encoding/HINTS.md

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+# Hints
+
+## General
+
+- Use `?` to work with the character [code points][codepoint].
+- `\s` can be used to represent a space.
+- Use [integer binary notation][integer-literal] for working with the codes.
+- Try to use the tail call recursion strategy.
+
+## 1. Encode nucleic acid to binary value
+
+- This function needs to map one integer to another.
+- Making use of multiple clause functions may make this easier by breaking it down.
+
+## 2. Decode the binary value to the nucleic acid
+
+- This function is the opposite of part 1's function.
+- Making use of multiple clause functions may make this easier by breaking it down.
+
+## 3. Encode a DNA charlist
+
+- Create a recursive function which takes a code point from the charlist and recursively builds the bitstring result.
+- Remember, a [charlist][charlist] is a list of [integer code points][codepoint].
+- You can get the first and remaining items from a list using a build in [`Kernel` module][kernel] function.
+- You can also pattern match on a list using the [`[head | tail]`][list] notation.
+- Use multiple clause functions to separate the base case from the recursive cases.
+- Do not forget to specify the types of bitstring segments using the `::` operator.
+
+## 4. Decode a DNA bitstring
+
+- Create a recursive function which [matches the first 4 bits][bitstring-matching] from the [bitstring][bitstring] and recursively builds the [charlist][charlist] result.
+- Remember the [bitstring special form][bitstring-form] can be used for matching on bitstrings.
+- Do not forget to specify the types of bitstring segments using the `::` operator.
+- You will need to reverse the accumulator at the end. Write a private tail-recursive `reverse` function to do that and use it in the base-case of the `decode` function.
+
+[integer-literal]: https://hexdocs.pm/elixir/master/syntax-reference.html#integers-in-other-bases-and-unicode-code-points
+[codepoint]: https://elixir-lang.org/getting-started/binaries-strings-and-char-lists.html#unicode-and-code-points
+[charlist]: https://elixir-lang.org/getting-started/binaries-strings-and-char-lists.html#charlists
+[bitstring]: https://elixir-lang.org/getting-started/binaries-strings-and-char-lists.html#bitstrings
+[bitstring-form]: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#%3C%3C%3E%3E/1
+[bitstring-matching]: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#%3C%3C%3E%3E/1-binary-bitstring-matching
+[type-operator]: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#::/2
+[recursion-tco]: https://en.wikipedia.org/wiki/Tail_call
+[list]: https://hexdocs.pm/elixir/List.html#content
+[kernel]: https://hexdocs.pm/elixir/Kernel.html#functions

elixir/dna-encoding/README.md

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+# DNA Encoding
+
+Welcome to DNA Encoding on Exercism's Elixir Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)
+
+## Introduction
+
+## Bitstrings
+
+Working with binary data is an important concept in any language, and Elixir provides an elegant syntax to write, match, and construct binary data.
+
+In Elixir, binary data is referred to as the bitstring type. The binary data*type* (not to be confused with binary data in general) is a specific form of a bitstring, which we will discuss in a later exercise.
+
+Bitstring literals are defined using the bitstring special form `<<>>`. When defining a bitstring literal, it is defined in segments. Each segment has a value and type, separated by the `::` operator. The type specifies how many bits will be used to encode the value. If the value of the segment overflows the capacity of the segment's type, it will be truncated from the left.
+
+```elixir
+# This defines a bitstring with three segments of a single bit each
+<<0::1, 1::1, 0::1>> == <<0::size(1), 1::size(1), 0::size(1)>>
+# => true
+<<0::1, 1::1, 0::1>> == <<2::size(3)>>
+# => true
+<<2::1>> == <<0::1>>
+# => true because of value overflow
+```
+
+When writing binary integer literals, we can write them directly in base-2 notation by prefixing the literal with `0b`.
+
+```elixir
+value = 0b11111011011 = 2011
+```
+
+By default, bitstrings are displayed in chunks of 8 bits (a byte).
+
+```
+<<value::11>>
+# => <<251, 3::size(3)>>
+```
+
+### Constructing
+
+We can combine bitstrings stored in variables using the special form:
+
+```elixir
+first = <<0b110::3>>
+second = <<0b001::3>>
+combined = <<first::bitstring, second::bitstring>>
+# => <<49::size(6)>>
+```
+
+### Pattern matching
+
+Pattern matching can also be done to obtain the value from within the special form:
+
+```elixir
+<<value::4, rest::bitstring>> = <<0b01101001::8>>
+value == 0b0110
+# => true
+```
+
+## Tail Call Recursion
+
+When [recursing][exercism-recursion] through enumerables (lists, bitstrings, strings), there are often two concerns:
+
+- how much memory is required to store the trail of recursive function calls
+- how to build the solution efficiently
+
+To deal with these concerns an _accumulator_ may be used.
+
+An accumulator is a variable that is passed along in addition to the data. It is used to pass the current state of the function's execution, from function call to function call, until the _base case_ is reached. In the base case, the accumulator is used to return the final value of the recursive function call.
+
+Accumulators should be initialized by the function's author, not the function's user. To achieve this, declare two functions - a public function that takes just the necessary data as arguments and initializes the accumulator, and a private function that also takes an accumulator. In Elixir, it is a common pattern to prefix the private function's name with `do_`.
+
+```elixir
+# Count the length of a list without an accumulator
+def count([]), do: 0
+def count([_head | tail]), do: 1 + count(tail)
+
+# Count the length of a list with an accumulator
+def count(list), do: do_count(list, 0)
+
+defp do_count([], count), do: count
+defp do_count([_head | tail], count), do: do_count(tail, count + 1)
+```
+
+The usage of an accumulator allows us to turn recursive functions into _tail-recursive_ functions. A function is tail-recursive if the _last_ thing executed by the function is a call to itself.
+
+[exercism-recursion]: https://exercism.org/tracks/elixir/concepts/recursion
+
+## Instructions
+
+In your DNA research lab, you have been working through various ways to compress your research data to save storage space. One teammate suggests converting the DNA data to a binary representation:
+
+| Nucleic Acid | Code   |
+| ------------ | ------ |
+| a space      | `0000` |
+| A            | `0001` |
+| C            | `0010` |
+| G            | `0100` |
+| T            | `1000` |
+
+You ponder this, as it will potentially halve the required data storage costs, but at the expense of human readability. You decide to write a module to encode and decode your data to benchmark your savings.
+
+## 1. Encode nucleic acid to binary value
+
+Implement `encode_nucleotide/1` to accept the code point for the nucleic acid and return the integer value of the encoded code.
+
+```elixir
+DNA.encode_nucleotide(?A)
+# => 0b0001
+```
+
+## 2. Decode the binary value to the nucleic acid
+
+Implement `decode_nucleotide/1` to accept the integer value of the encoded code and return the code point for the nucleic acid.
+
+```elixir
+DNA.decode_nucleotide(0b0001)
+# => ?A
+```
+
+## 3. Encode a DNA charlist
+
+Implement `encode/1` to accept a charlist representing nucleic acids and gaps and return a bitstring of the encoded data.
+
+```elixir
+DNA.encode('AC GT')
+# => <<18, 4, 8::size(4)>>
+```
+
+## 4. Decode a DNA bitstring
+
+Implement `decode/1` to accept a bitstring representing nucleic acids and gaps and return the decoded data as a charlist.
+
+```elixir
+DNA.decode(<<132, 2, 1::size(4)>>)
+# => 'TG CA'
+```
+
+## Source
+
+### Created by
+
+- @neenjaw
+
+### Contributed to by
+
+- @angelikatyborska
+- @NobbZ

elixir/dna-encoding/lib/dna.ex

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+defmodule DNA do
+  def encode_nucleotide(code_point) do
+    # Please implement the encode_nucleotide/1 function
+  end
+
+  def decode_nucleotide(encoded_code) do
+    # Please implement the decode_nucleotide/1 function
+  end
+
+  def encode(dna) do
+    # Please implement the encode/1 function
+  end
+
+  def decode(dna) do
+    # Please implement the decode/1 function
+  end
+end

elixir/dna-encoding/mix.exs

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+defmodule DNA.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :dna,
+      version: "0.1.0",
+      # elixir: "~> 1.10",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end

elixir/dna-encoding/test/dna_test.exs

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+defmodule DNATest do
+  use ExUnit.Case
+
+  describe "encode to 4-bit encoding" do
+    @tag task_id: 1
+    test "?\\s to 0b0000", do: assert(DNA.encode_nucleotide(?\s) == 0b0000)
+    @tag task_id: 1
+    test "?A to 0b0001", do: assert(DNA.encode_nucleotide(?A) == 0b0001)
+    @tag task_id: 1
+    test "?C to 0b0010", do: assert(DNA.encode_nucleotide(?C) == 0b0010)
+    @tag task_id: 1
+    test "?G to 0b0100", do: assert(DNA.encode_nucleotide(?G) == 0b0100)
+    @tag task_id: 1
+    test "?T to 0b1000", do: assert(DNA.encode_nucleotide(?T) == 0b1000)
+  end
+
+  describe "decode to code point" do
+    @tag task_id: 2
+    test "0b0000 to ?\\s", do: assert(DNA.decode_nucleotide(0b0000) == ?\s)
+    @tag task_id: 2
+    test "0b0001 to ?A", do: assert(DNA.decode_nucleotide(0b0001) == ?A)
+    @tag task_id: 2
+    test "0b0010 to ?C", do: assert(DNA.decode_nucleotide(0b0010) == ?C)
+    @tag task_id: 2
+    test "0b0100 to ?G", do: assert(DNA.decode_nucleotide(0b0100) == ?G)
+    @tag task_id: 2
+    test "0b1000 to ?T", do: assert(DNA.decode_nucleotide(0b1000) == ?T)
+  end
+
+  describe "encoding" do
+    @tag task_id: 3
+    test "' '", do: assert(DNA.encode(' ') == <<0b0000::4>>)
+    @tag task_id: 3
+    test "'A'", do: assert(DNA.encode('A') == <<0b0001::4>>)
+    @tag task_id: 3
+    test "'C'", do: assert(DNA.encode('C') == <<0b0010::4>>)
+    @tag task_id: 3
+    test "'G'", do: assert(DNA.encode('G') == <<0b0100::4>>)
+    @tag task_id: 3
+    test "'T'", do: assert(DNA.encode('T') == <<0b1000::4>>)
+
+    @tag task_id: 3
+    test "' ACGT'",
+      do: assert(DNA.encode(' ACGT') == <<0b0000::4, 0b0001::4, 0b0010::4, 0b0100::4, 0b1000::4>>)
+
+    @tag task_id: 3
+    test "'TGCA '",
+      do: assert(DNA.encode('TGCA ') == <<0b1000::4, 0b0100::4, 0b0010::4, 0b0001::4, 0b0000::4>>)
+  end
+
+  describe "decoding" do
+    @tag task_id: 4
+    test "' '", do: assert(DNA.decode(<<0b0000::4>>) == ' ')
+    @tag task_id: 4
+    test "'A'", do: assert(DNA.decode(<<0b0001::4>>) == 'A')
+    @tag task_id: 4
+    test "'C'", do: assert(DNA.decode(<<0b0010::4>>) == 'C')
+    @tag task_id: 4
+    test "'G'", do: assert(DNA.decode(<<0b0100::4>>) == 'G')
+    @tag task_id: 4
+    test "'T'", do: assert(DNA.decode(<<0b1000::4>>) == 'T')
+
+    @tag task_id: 4
+    test "' ACGT'",
+      do: assert(DNA.decode(<<0b0000::4, 0b0001::4, 0b0010::4, 0b0100::4, 0b1000::4>>) == ' ACGT')
+
+    @tag task_id: 4
+    test "'TGCA '",
+      do: assert(DNA.decode(<<0b1000::4, 0b0100::4, 0b0010::4, 0b0001::4, 0b0000::4>>) == 'TGCA ')
+  end
+end

elixir/dna-encoding/test/test_helper.exs

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+ExUnit.start()
+ExUnit.configure(exclude: :pending, trace: true, seed: 0)