 # davearonson's solution

## to Wordy in the Elixir Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Parse and evaluate simple math word problems returning the answer as an integer.

What is 5 plus 13?

Evaluates to 18.

Handle large numbers and negative numbers.

## Iteration 2 — Subtraction, Multiplication and Division

Now, perform the other three operations.

What is 7 minus 5?

2

What is 6 multiplied by 4?

24

What is 25 divided by 5?

5

## Iteration 3 — Multiple Operations

Handle a set of operations, in sequence.

Since these are verbal word problems, evaluate the expression from left-to-right, ignoring the typical order of operations.

What is 5 plus 13 plus 6?

24

What is 3 plus 2 multiplied by 3?

15 (i.e. not 9)

## Bonus — Exponentials

If you'd like, handle exponentials.

What is 2 raised to the 5th power?

32

## Running tests

Execute the tests with:

``````\$ elixir wordy_test.exs
``````

### Pending tests

In the test suites, all but the first test have been 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:

``````# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
``````

Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the test suite.

``````# ExUnit.configure exclude: :pending, trace: true
``````

For more detailed information about the Elixir track, please see the help page.

## Source

Inspired by one of the generated questions in the Extreme Startup game. https://github.com/rchatley/extreme_startup

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### wordy_test.exs

``````if !System.get_env("EXERCISM_TEST_EXAMPLES") do
end

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

defmodule WordyTest do
use ExUnit.Case

assert Wordy.answer("What is 1 plus 1?") == 2
end

@tag :pending
assert Wordy.answer("What is 53 plus 2?") == 55
end

@tag :pending
test "addition with negative numbers" do
assert Wordy.answer("What is -1 plus -10?") == -11
end

@tag :pending
assert Wordy.answer("What is 123 plus 45678?") == 45801
end

@tag :pending
test "subtraction" do
assert Wordy.answer("What is 4 minus -12?") == 16
end

@tag :pending
test "multiplication" do
assert Wordy.answer("What is -3 multiplied by 25?") == -75
end

@tag :pending
test "division" do
assert Wordy.answer("What is 33 divided by -3?") == -11
end

@tag :pending
assert Wordy.answer("What is 1 plus 1 plus 1?") == 3
end

@tag :pending
assert Wordy.answer("What is 1 plus 5 minus -2?") == 8
end

@tag :pending
test "multiple subtraction" do
assert Wordy.answer("What is 20 minus 4 minus 13?") == 3
end

@tag :pending
assert Wordy.answer("What is 17 minus 6 plus 3?") == 14
end

@tag :pending
test "multiple multiplication" do
assert Wordy.answer("What is 2 multiplied by -2 multiplied by 3?") == -12
end

@tag :pending
assert Wordy.answer("What is -3 plus 7 multiplied by -2?") == -8
end

@tag :pending
test "multiple division" do
assert Wordy.answer("What is -12 divided by 2 divided by -3?") == 2
end

@tag :pending
test "unknown operation" do
assert_raise ArgumentError, fn ->
end
end

@tag :pending
test "Non math question" do
assert_raise ArgumentError, fn ->
Wordy.answer("Who is the President of the United States?")
end
end
end``````
``````defmodule Wordy do

@doc """
Calculate the math problem in the sentence.
"""
# scan for hits composed of:
# any string of non-digits (and stash it), a space,
# and an optional minus sign followed by digits (and stash it and them).
# at this point we're not bothering to validate the non-number part.
pieces = Regex.scan(~r/([^\d]*) (-?\d+)/, question)
# if we got no hits, or there is more (or less!) left over than a "?",
# then the question is malformed. it may be malformed in other ways,
# that will raise no-matching-clause errors below.
if pieces == nil || remove_pieces(pieces, question) != "?" do
raise ArgumentError
end
fixed = pieces |> Enum.map(&fixup/1)
end

defp remove_pieces([[whole_hit|_]|more], question) do
remove_pieces(more, question |> String.replace(whole_hit, ""))
end

defp remove_pieces([], question), do: question

# match on nil means it must be the very first thing.
# anything else as first thing will also produce error
# when we try to do math with it in the other defps.
end

end

end

end

end

defp do_answer(_, _), do: raise ArgumentError

defp fixup([_|[words|[number]]]) do
[String.trim(words), String.to_integer(number)]
end
end``````