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Asked: 2026-05-23T09:36:28+00:00

Here is my code: is_prime(Num)-> length(list_of_dividers(Num)) == 0. problem_7(Current, Primes, Counter) when Primes >=

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Here is my code:

is_prime(Num)->
    length(list_of_dividers(Num)) == 0.

problem_7(Current, Primes, Counter) when Primes >= 10001->
    Current;
problem_7(Current, Primes, Counter) when is_prime(Counter) ->
    problem_7(Counter, Primes + 1, Counter + 1);
problem_7(Current, Primes, Counter) ->
    problem_7(Current, Primes, Counter).

I get error:

32> c(problem_7).
./problem_7.erl:30: call to local/imported function is_prime/1 is illegal in guard

And i can not use local function in the ‘if’-expression:

if is_prime(Counter)->
    problem_7(Counter, Primes + 1, Counter + 1);
   true ->
    problem_7(Current, Primes, Counter + 1)
end.

I am just wondering if there is any way to use local function in guard and how can I write condition with local function?

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1 Answer

  1. Editorial Team

    The reason for restricting the set of valid expressions is that evaluation of a guard expression must be guaranteed to be free of side effects. http://www.erlang.org/doc/reference_manual/expressions.html (section 7.24)

    Use case statement inside your function. You should be able to use local function in if and case.

    Edited: Agree with @cthulahoops, I was wrong about if http://www.erlang.org/doc/reference_manual/expressions.html#id75927

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