%LEN and *ZERO


This question is for Hans or Barbara (or anyone else who knows):

Why does the RPG IV compiler reject the following line with RNF7563?

        C                       EVAL %LEN(cmdString) = *ZERO

when cmdString is defined as:

        D cmdString             S               5768    VARYING

I see the documentation says:

        "The parameter must not be a figurative constant."

but that suggests to me the parameter of the BIF cannot be a figurative 
constant (e.g., something stupid like x = %LEN(*HIVAL)) not that I can't used 
a figurative constant to assign the current length.

I want to know why they can't be used.  I can understand rejecting many of the 
figurative constants but rejecting *ZERO seems a bit short-sighted to me.  
What is the real difference between the failing line and the following:

        C                       EVAL %LEN(cmdString) = 0

which is accepted by the compiler.

Especially in view of the fact that the compiler is quite happy with a 
construct like:

        C                       IF      %LEN(cmdString) = *ZERO

I would expect %LEN(cmdString) = *ZERO to set the length to zero; 
%LEN(cmdString) = *HIVAL to set the length to 99999 since the length component 
is a BIN(2) and to generate an error if the declared length is less than 
99999; %LEN(cmdString) = *LOVAL to generate an error because you can't have a 
negative length -- although there is a reasonable argument that *LOVAL should 
be the same as *ZERO in this case because the smallest variable length value 
is zero.

In the words of a famous, now dead, Australian; Why is it so?

I can feel a PMR coming on ....

Regards,
Simon Coulter.

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