Sorry, I send it accidently. I did't finish my question.

Anyway, when I run in GHCi:

userRegistration  ("Joao Claudino","1240",2) users


It gives me the exception:

*** Exception: Prelude.head: empty list

Can anyone explain to me why the exception is thown and what should I do to fix it?

Thanks
 
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Francisco Borges "Chicão" Junior
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http://pedepinico.blogspot.com
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"Quem de boa vontade carrega o difícil, também carrega o menos difícil..." Lao Tsé - Tao Te Ching