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POUse of function in Guard not allowed. Suggestions for alternate implementation wanted
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copied!<p>I am attempting to create a prime number factorizer, using <a href="http://en.wikipedia.org/wiki/Fermat%27s_factorization_metho" rel="nofollow noreferrer">fermats method</a>.</p> <p>This line generates an error</p> <pre><code>find_factors(A, B, FactorThis) when is_a_square(B) == true -> </code></pre> <p><strong>call to local/imported function is_a_square/1 is illegal in guard</strong></p> <p>The only possible alternative I see to this implementation is to use some sort of case statement within the function. I was avoiding that, as it might screw up the tail recursion. I am a Erlang noob. <strong>What other ways are there to implement this functionality?</strong></p> <pre><code>get_int_part_of_sqrt(N) -> trunc(math:sqrt(N)). is_a_square(N) -> get_int_part_of_sqrt(N) * get_int_part_of_sqrt(N) == N. calculate_new_b(A, FactorThis) -> NewB = trunc(abs((A * A) - FactorThis)), io:format("Calculate_new_b A^2 ~w- FT ~w= NB ~w ~n",[A*A,FactorThis,NewB]), find_factors(A, B, FactorThis) when is_a_square(B) == true -> io:format("find_factors true ~w ~w~n", [A, B]), {ok, A + get_int_part_of_sqrt(B), A - get_int_part_of_sqrt(B)}; find_factors(A, B, FactorThis) -> io:format("find_factors false ~w ~w~n", [A, B]), NewA = A + 1, NewB = calculate_new_b(NewA, FactorThis), find_factors(NewA, NewB, FactorThis). </code></pre> <p><a href="https://stackoverflow.com/questions/2241340/unable-to-use-function-call-in-function-guard">Research1</a> </p> <p><a href="https://stackoverflow.com/questions/6505213/is-there-a-way-to-use-local-function-in-guard">Research2</a> </p> <p>Edited. fixed argument in call to calculate_new_b</p> <p>added missing get_int_part_of_sqrts.</p>

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