You're probably not passing a symbol for the second argument:

julia> isdefined(:sum)
true

julia> isdefined(:foo)
false

julia> isdefined(Base, :foo)
false

julia> isdefined(Base, :sum)
true


If you call isdefined(foo), then it first tries to evaluate the variable 
"foo" and pass the result to "isdefined", but evaluating "foo" throws an 
error if "foo" is not defined.   In contrast, :foo is a symbolic expression 
that refers to the "symbol" foo, which it doesn't try to evaluate. 

On Thursday, May 22, 2014 3:19:41 PM UTC-4, Cirrus McInnis wrote:
>
> New to Julia..
>
> I'm just trying to test for a var's existence.   isdefined()  seems to be 
> the tool to use.
> If the result is true then "true" is returned.
> If false, "x not defined.." is returned.  Shouldn't it return "false"?
>
> Is there another way to test for existence?
>
> -David
>

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