[erlang-questions] learning Erlang: factoring primes

[Matthias Lang]

The programming style is fine. I only see trivial things which are
hardly worth mentioning:

  - You don't need to quote atoms like 'factor' (in your compile comment)
  - The program currently hangs for negative numbers

It can be simplified a bit, though it's already pretty good. You can
rewrite next_factor in two clauses like this:

  first_factor(N, M) when N rem M == 0 -> 
    M;
  first_factor(N, M) -> 
    first_factor(N, M+1).

Matthias


Martin Ankerl writes:
 > Hello everybody, I have just started learning Erlang and wrote one of
 > my first programs. It is a very simple prime factoring program, but it
 > works. I would appreciate comments about the programming style, is
 > this how Erlang code should be written? Any way to make it simpler?
 > 
 > Here is the code:
 > 
 > -module(factor).
 > -export([fact/1]).
 > 
 > % c('factor').
 > % factor:fact(123456723456789).
 > fact(1) ->
 >         [];
 > fact(N) ->
 >         % io:format("~w\n", [N]),
 >         M = next_factor(N, 2, N rem 2),
 >         [ M | fact(N div M) ].
 > 
 > % find the next factor
 > next_factor(_, M, 0) ->
 >         M;
 > next_factor(N, N, _) ->
 >         N;
 > next_factor(N, M, _) ->
 >         next_factor(N, M+1, N rem (M+1)).
 > 
 > -- 
 > Martin Ankerl | http://martin.ankerl.com
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