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sudhagarc's solution

to Allergies in the Erlang Track

Published at Oct 14 2020 · 0 comments
Test suite


This exercise has changed since this solution was written.

Given a person's allergy score, determine whether or not they're allergic to a given item, and their full list of allergies.

An allergy test produces a single numeric score which contains the information about all the allergies the person has (that they were tested for).

The list of items (and their value) that were tested are:

  • eggs (1)
  • peanuts (2)
  • shellfish (4)
  • strawberries (8)
  • tomatoes (16)
  • chocolate (32)
  • pollen (64)
  • cats (128)

So if Tom is allergic to peanuts and chocolate, he gets a score of 34.

Now, given just that score of 34, your program should be able to say:

  • Whether Tom is allergic to any one of those allergens listed above.
  • All the allergens Tom is allergic to.

Note: a given score may include allergens not listed above (i.e. allergens that score 256, 512, 1024, etc.). Your program should ignore those components of the score. For example, if the allergy score is 257, your program should only report the eggs (1) allergy.

Running tests

In order to run the tests, issue the following command from the exercise directory:

For running the tests provided, rebar3 is used as it is the official build and dependency management tool for erlang now. Please refer to the tracks installation instructions on how to do that.

In order to run the tests, you can issue the following command from the exercise directory.

$ rebar3 eunit


For detailed information about the Erlang track, please refer to the help page on the Exercism site. This covers the basic information on setting up the development environment expected by the exercises.


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%% Based on canonical data version 1.1.0
%% https://github.com/exercism/problem-specifications/raw/master/exercises/allergies/canonical-data.json
%% This file is automatically generated from the exercises canonical data.



'1_no_allergies_means_not_allergic_test'() ->
    ?assertNot(allergies:is_allergic_to(peanuts, 0)),
    ?assertNot(allergies:is_allergic_to(cats, 0)),
    ?assertNot(allergies:is_allergic_to(strawberries, 0)).

'2_is_allergic_to_eggs_test'() ->
    ?assert(allergies:is_allergic_to(eggs, 1)).

'3_allergic_to_eggs_in_addition_to_other_stuff_test'() ->
    ?assert(allergies:is_allergic_to(eggs, 5)),
    ?assert(allergies:is_allergic_to(shellfish, 5)),
    ?assertNot(allergies:is_allergic_to(strawberries, 5)).

'4_no_allergies_at_all_test'() ->
    ?assertMatch([], lists:sort(allergies:allergies(0))).

'5_allergic_to_just_eggs_test'() ->

'6_allergic_to_just_peanuts_test'() ->

'7_allergic_to_just_strawberries_test'() ->

'8_allergic_to_eggs_and_peanuts_test'() ->
    ?assertMatch([eggs, peanuts],

'9_allergic_to_more_than_eggs_but_not_peanuts_test'() ->
    ?assertMatch([eggs, shellfish],

'10_allergic_to_lots_of_stuff_test'() ->
    ?assertMatch([cats, chocolate, pollen, strawberries,

'11_allergic_to_everything_test'() ->
    ?assertMatch([cats, chocolate, eggs, peanuts, pollen,
		  shellfish, strawberries, tomatoes],

'12_ignore_non_allergen_score_parts_test'() ->
    ?assertMatch([cats, chocolate, eggs, pollen, shellfish,
		  strawberries, tomatoes],

-export([allergies/1, is_allergic_to/2]).

-define(ALLERGIES, [{eggs, 1}, {peanuts, 2}, {shellfish, 4}, 
                    {strawberries, 8}, {tomatoes, 16}, 
                    {chocolate, 32}, {pollen, 64}, {cats, 128}]).

allergies(GivenScore) ->
    [Sub || {Sub, Score} <- ?ALLERGIES, (GivenScore band Score) =/= 0].

is_allergic_to(Substance, Score) -> 
    lists:any(fun({Sub, Sco}) -> Sub =:= Substance andalso (Sco band Score) =/= 0 end, ?ALLERGIES).

What can you learn from this solution?

A huge amount can be learned from reading other peopleโ€™s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?