[erlang-questions] Don't understand the error message: call to local/imported function ... is illegal in guard

[Donald Steven]

Thanks Yao.

On 12/23/2018 8.02 PM, by wrote:
> Only limited expressions are permitted after “if”(guard), and the user defined function does not in the list.
> I believe there is a list on Erlang Doc about what is permitted.
>
> By the way, this limitation is for avoiding side effects when evaluating expressions.
>
> Yao
>
>> 在 2018年12月24日，08:26，Donald Steven <t6sn7gt@REDACTED> 写道：
>>
>> This code works:
>>
>>      AlphaNumericChar = isAlphaNumeric(C),
>>      if AlphaNumericChar ->
>>
>> but this code (which is functionally identical):
>>
>>      if isAlphaNumeric(C) ->
>>
>> produces an error message: call to local/imported function isAlphaNumeric/1 is illegal in guard
>>
>> Why?
>>
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