# 176. Because recursive I/O is prohibited, a function should use ERROR STOP msg instead of PRINT statements for error messages.
topic: {ref}`input-and-output`
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Because recursive I/O is prohibited, a function should not have PRINT or WRITE(*,fmt) statements for error messages, since the behavior of
print*,f(x)
is then undefined. ERROR STOP <msg> is an alternative. Internal write can be useful in a function.
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