An attempt to learn Elixir by working through some Katas.
See commit messages for notes and details.
Tests can be executed by running mix test
Problem:
Convert Arabic versions of numbers to their equivalent Roman numeral versions.
File:
- Module:
lib/rn.ex - Tests:
test/rn_test.exs
Functions:
Rn.romanize/1- Returns the Roman numeral equivalent for a given number
Problem:
By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.
Files:
- Module:
lib/fib.ex - Tests:
test/fib_test.ex
Functions:
fib/1- _returns the n-th number in the Fibonacci sequence
sum_of_evens_to/1- _returns the sum of the even numbers in the sequence up to the point where the highest number does not excede a given limit.
Problem:
Find the sum of all the multiples of 3 or 5 below 1000.
Files:
- Module:
lib/threes_and_fives.ex - Tests:
test/threes_and_fives_test.exs
Functions:
ThreesAndFives.sum_of_multiples_to/1- returns the sum of all the multiples of three and five less than the given limit
Problem:
(Exercise "ListsAndRecursion-1" from Programming Elixir ≥ 1.6 by Dave Thomas)
“Write a mapsum function that takes a list and a function. It applies the function to each element of the list and then sums the result, so
iex> MyList.mapsum [1, 2, 3], &(&1 * &1)
14
Obviously this could easly be done using Enum.reduce/3 or Enum.map/2 |> Enum.sum/1:
- cheating 1:
Enum.reduce(list, 0, & f.(&1) + &2) - cheating 2:
Enum.map(list, f) |> Enum.sum()
But I think the point of the exercise is to use recursion to recreate the reduce funtionality.
Files:
lib/prag_prog/my_list.extest/prag_prog/my_list_test.exs
Functions:
PragProg.MyList.mapsum/2- applies a function to the given list and returns the sum of all the results
Problem:
(Exercise "ListsAndRecursion-2" from Programming Elixir ≥ 1.6 by Dave Thomas)
“Write a max(list) that returns the element with the maximum value in the list. (This is slightly trickier than it sounds.)”
Files:
- Module:
lib/prag_prog/my_list.ex - Tests:
test/prag_prog/my_list_test.exs
Functions:
PragProg.MyList.max/1
Problem:
(Exercise "ListsAndRecursion-3" from Programming Elixir ≥ 1.6 by Dave Thomas)
“An Elixir single-quoted string is actually a list of individual character codes. Write a caesar(list, n) function that adds n to each list element, wrapping if the addition results in a character greater than z."
iex> MyList.caesar('ryvkve', 13)
?????? :)
Files:
- Module:
lib/prag_prog/my_list.ex - Tests:
test/prag_prog/my_list_test.exs
Functions:
PragProg.MyList.caesar/2
Problem:
(Exercise "ListsAndRecursion-4" from Programming Elixir ≥ 1.6 by Dave Thomas)
“Write a function MyList.span(from, to) that returns a list of the numbers from from up to to.”
I assume this means to not use the obvious Enum.to_list(from..to), but to reimplement it with a new method to achieve the same effect.
Files:
- Module:
lib/prag_prog/my_list.ex - Tests:
test/prag_prog/my_list_test.exs
Functions:
PragProg.MyList.span/2
Problem:
(Exercise "ListsAndRecursion-5" from Programming Elixir ≥ 1.6 by Dave Thomas)
“Implement the following Enum functions using no library functions or list comprehensions: all?, each, filter, split, and take.”
Files:
- Module:
lib/prag_prog/my_list.ex - Tests:
test/prag_prog/my_list_test.exs
Functions:
PragProg.MyList.all?/2- returns true if all elemements of a list return a truthy value when applied to a given function.
PragProg.MyList.any?/2- returns true if any elemement of a list return a truthy value when applied to a given function.
PragProg.MyList.each/2- invokes the given fun for each element in a list.
PragProg.MyList.filter/2- returns a list of all elements of a list that return a truthy value when applied to a given function.
PragProg.MyList.split/3- returns the elements of a list within a given range.
- (ignoring negative values and range boundries for now)
PragProg.MyList.take/2- returns the first n number of elements in a list
- (ignoring negative values and range boundries for now)
Problem:
(Exercise "ListsAndRecursion-6" from Programming Elixir ≥ 1.6 by Dave Thomas)
"(Hard) Write a flatten(list) function that takes a list that may contain any number of sublists, which themselves may contain sublists, to any depth. It returns the elements of these lists as a flat list.”
iex> MyList.flatten([ 1, [ 2, 3, [4] ], 5, [[[6]]] ])
[1,2,3,4,5,6]
Hint: You may have to use Enum.reverse to get your result in the correct order.”
Files:
- Module:
lib/prag_prog/my_list.ex - Tests:
test/prag_prog/my_list_test.exs
Functions:
PragProg.MyList.flatten/1- returns a flat list containing all the elements of a given list containing any number of nested sublists.
Problem:
(Exercise "ListsAndRecursion-8" from Programming Elixir ≥ 1.6 by Dave Thomas)
“The Pragmatic Bookshelf has offices in Texas (TX) and North Carolina (NC), so we have to charge sales tax on orders shipped to these states. The rates can be expressed as a keyword list (I wish it were that simple.…):
tax_rates = [ NC: 0.075, TX: 0.08 ]
Here’s a list of orders:
orders = [ [ id: 123, ship_to: :NC, net_amount: 100.00 ],
[ id: 124, ship_to: :OK, net_amount: 35.50 ],
[ id: 125, ship_to: :TX, net_amount: 24.00 ],
[ id: 126, ship_to: :TX, net_amount: 44.80 ],
[ id: 127, ship_to: :NC, net_amount: 25.00 ],
[ id: 128, ship_to: :MA, net_amount: 10.00 ],
[ id: 129, ship_to: :CA, net_amount: 102.00 ],
[ id: 130, ship_to: :NC, net_amount: 50.00 ]
]
Write a function that takes both lists and returns a copy of the orders, but with an extra field, total_amount, which is the net plus sales tax. If a shipment is not to NC or TX, there’s no tax applied."
Files:
lib/prag_prog/orders.extest/prag_prog/orders_test.exs
Functions:
- PragProg.calc_totals/2
Problem:
(Exercise "StringsAndBinaries-5" from Programming Elixir ≥ 1.6 by Dave Thomas)
"Write a function that takes a list of double-quoted strings and prints each on a separate line, centered in a column that has the width of the longest string. Make sure it works with UTF characters."
iex> center(["cat", "zebra", "elephant"])
cat
zebra
elephant
Files:
lib/prag_prog/my_string.extest/prag_prog/my_string_test.exs
Functions:
PragProg.MyString.center/1
Problem:
"Write a function to capitalize the sentences in a string.
Each sentence is terminated by a period and a space. Right now, the case of the characters in the string is random."
iex> capitalize_sentences("oh. a DOG. woof. ")
"Oh. A dog. Woof. "
Files:
lib/prag_prog/my_string.extest/prag_prog/my_string_test.exs
Functions:
PragProg.MyString.sentence_case/1
Problem:
"Chapter 7 had an exercise about calculating sales tax. We now have the sales information in a file of comma-separated id, ship_to, and amount values. The file looks like this:"
id,ship_to,net_amount
123,:NC,100.00 124,:OK,35.50
125,:TX,24.00 126,:TX,44.80
127,:NC,25.00 128,:MA,10.00
129,:CA,102.00 120,:NC,50.00
Write a function that reads and parses this file and then passes the result to the sales_tax function. Remember that the data should be formatted into a keyword list, and that the fields need to be the correct types (so the id field is an integer, and so on).
You’ll need the library functions File.open, IO.read(file, :line), and IO.stream(file).
Files:
lib/prag_prog/orders.extest/prag_prog/orders_test.exs
Functions:
PragProg.Orders.parse_file/1PragProg.Orders.calc_totals/2
Problem:
(Exercise "MoreCoolStuff-1" from Programming Elixir ≥ 1.6 by Dave Thomas)
"Write a sigil ~v that parses multiple lines of comma-separated data, returning a list where each element is a row of data and each row is a list of values. Don’t worry about quoting—just assume each field is separated by a comma."
For example
csv = ~v"""
1,2,3
cat,dog
"""
would generate
[["1","2","3"], ["cat","dog"]]
(Exercise "MoreCoolStuff-2" from Programming Elixir ≥ 1.6 by Dave Thomas)
"The function Float.parse converts leading characters of a string to a float, returning either a tuple containing the value and the rest of the string, or the atom :error.
Update your CSV sigil so that numbers are automatically converted:
csv = ~v"""
1,2,3.14
cat,dog
"""
should generate
[[1.0,2.0,3.14], ["cat","dog"]]
(Exercise "MoreCoolStuff-3" from Programming Elixir ≥ 1.6 by Dave Thomas)
(Hard) Sometimes the first line of a CSV file is a list of the column names. Update your code to support this, and return the values in each row as a keyword list, using the column names as the keys. Here’s an example:
csv = ~v"""
Item,Qty,Price
Teddy bear,4,34.95
Milk,1,2.99
Battery,6,8.00
"""
would generate
[
[Item: "Teddy bear", Qty: 4, Price: 34.95],
[Item: "Milk", Qty: 1, Price: 2.99],
[Item: "Battery", Qty: 6, Price: 8.00]
]
Files:
lib/prag_prog/csv_sigil.extest/prag_prog/csv_sigil_test.exs
Functions:
PragProg.CSVSigil.v_sigil/2
_Note: this function is not called directly. Instead, a consuming module (e.g. PragProg.CSVSigilTest) should use PragProg.CSVSigil, allowing it to then use the sigil (~v[...]) within its functions.