ev - diff error?



Stavros Macrakis <macrakis <at> alum.mit.edu> writes:

> 
> When you say
> 
> ? ? ?ev(diff(sin(x),x),x=1);?
> 
> You are asking Maxima to calculate diff(sin(x),x) in a 
context where all x's
are replaced by 1.
> 
> ? ? ? ? ? ? -s
> 
> 
> 

Thank you very much for your quick reply.
I am still puzzled by the fact that 
ev(diff(sin(x),x), x=%pi) returns 0
instead of an error. such as in the case of 
ev(diff(sin(x),x), x=%pi/4).