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I was under the impression MMA directly substituted everything when assigned. Obviously I'm missing something subtle with either how substitution works in a notebook or how the Disk function takes an expression. (I guess the 3rd option might be that it's some sort of graphical bug in the WebGL performance of MMA online.) Do I need to change the Head of the "d" expression? How do I do that? This is a simplified version of a Neat Example for Disk in Wolfram doc center. In any case, I'd really like to learn about what's going on here. 

Graphics[Table[Disk[RandomReal[4,{2}],RandomReal[1]],40]]

enter image description here

Clear[d];
d:={RandomReal[4,{2}],RandomReal[1]}
Graphics[Table[Disk[d],40]]

enter image description here

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    $\begingroup$ It is a {} issue. You have many of them. Try this Graphics[Table[Disk[Sequence@@d],40]] and see if it works for you. $\endgroup$ Commented Oct 17, 2017 at 3:26
  • $\begingroup$ Yes that fixed it. Did you want to answer this? Sequence:"represents a sequence of arguments to be spliced automatically into any function." $\endgroup$ Commented Oct 17, 2017 at 3:30

2 Answers 2

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Passing the result of d as sequence resolves the extra {} issue.

From help

Mathematica graphics

So this should now work

Clear[d];
d:={RandomReal[4,{2}],RandomReal[1]}
Graphics[Table[Disk[Sequence@@d],40]]

Mathematica graphics

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  • $\begingroup$ Boom. The internet works! Problem solved. Thank you! $\endgroup$ Commented Oct 17, 2017 at 3:34
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Alternatives.

SeedRandom[42]
d := {RandomReal[4, {2}], RandomReal[1]}
Graphics[Table[Disk @@ d, 40]]

SeedRandom[42]
d := Sequence[RandomReal[4, {2}], RandomReal[1]]
Graphics[Table[Disk @ d, 40]]

Both produce

blobs

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