Erlang. Упражнения.

В рамках программы изучения Erlang я делаю упражнения из книги «Erlang programming» Франческо Чезарини и Саймона Томпсона. Оказалось что это на редкость полезное занятие, – теперь синтаксис не кажется таким уж страшным, и решение хоть и простых, но практических задач, придает уверенности в себе. Ниже я приведу условия задачи (уж простите, без перевода) и свой вариант решения (зачастую не оптимальный).

Exercise 3-1: Evaluating Expressions

Write a function sum/1which, given a positive integer N, will return the sum of all the integers between 1 and N.

Example: sum(5) ⇒ 15.

Write a function sum/2which, given two integers N and M, where N =< M, will return the sum of the interval between N and M. If N > M, you want your process to terminate

sum(1,3) ⇒ 6.
sum(6,6) ⇒ 6.


listCreate(L, Start, End) ->
	Start < End -> listCreate(L ++ [End], Start, End - 1);
	true -> L

sum(N) ->
  %Res = listCreate([], 0, N),
  %io:format("~w~n", [Res]),
  lists:sum(listCreate([], 0, N)).

sum(Start, End) ->
  lists:sum(listCreate([], Start, End)).

start() ->  
  io:format("~w~n~w~n", [sum(5), sum(1,3)]).

Exercise 3-2: Creating Lists

Write a function that returns a list of the format [1,2,..,N-1,N].

create(3) ⇒ [1,2,3].

Write a function that returns a list of the format [N, N-1,..,2,1].

reverse_create(3) ⇒ [3,2,1].


create(List, 0) -> List;
create(List, N) -> create(List ++ [N], N - 1).
create(N) -> create([], N).

start() ->

Exercise 3-3: Side Effects

Write a function that prints out the integers between 1 and N.

Hint: use io:format(“Number:~p~n”,[N]).

Write a function that prints out the even integers between 1 and N.

Hint: use guards.

-module (test3_3).
-import (io).
-export ([start/0]).

% implementation with if
print(Max, Cur) ->
  NewCur = Cur + 1,
    Max > Cur ->
      print(Max, NewCur);
    true -> io:format("Number:~p~n",[NewCur])

print(Max) ->
  print(Max - 1, 0).

% implementation with guard
print1(Max, Min) when Max > Min ->
  NewCur = Min + 1,
  print1(Max, NewCur);
print1(_, _) -> false.

print1(Max) -> 
  print1(Max, 0).

start() ->
%  print(3).

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