chapter_5

Exercises for Chapter 5

1. Write some functions to read configuration files containing JSON and turn them into Erlang maps. Also write code to validate the data in the configuration files.

Unlike what's shown in the book, the map module doesn't actually have a to_json/1 and from_json/1 functions. jsx is a JSON library that has similar functions, so we will use it instead. Solution to the exercise is in the exercise_1 directory. Example usage:

1> json_configuration:config_to_map("sample_config.json").
[{<<"param1">>,<<"value1">>},
 {<<"param2">>,<<"value2">>},
 {<<"param3">>,[<<"one">>,<<"two">>,<<"three">>]},
 {<<"param4">>,[]},
 {<<"param5">>,
  [{<<"sub1">>,<<"test1">>},{<<"sub2">>,<<"test2">>}]}]
2> json_configuration:verify_config("sample_config.json").
true

2. Write a function named map_search_pred that takes a map Map and a predicate Pred that returns the first element which Pred returns true.

Solution to the exercise is in the exercise_2 directory. Example usage:

% Function that returns true when the key is `baz`
1> Fun = fun(Key, Val) ->
1>   case Key of
1>     baz ->
1>       true;
1>     _ ->
1>       false
1>   end
1> end.
#Fun<erl_eval.12.54118792>

% Passing a map and the predicate function to `map_search_pred`
2> map_search:map_search_pred(#{first => 'Joe', last => 'Armstrong'}, Fun).
{baz,bim}
3>

3. Make an Erlang module with functions equivalent to the methods defined in Ruby's Hash class.

Solution to the exercise is in the exercise_3 directory.