Pattern to match list of identical elements

I am looking for a pattern that matches a (possibly empty) list consisting of identical (in the sense of Equal[]) atomic objects, but I can't figure it out. Any help would be greatly appreciated开发者_StackOverflow中文版.

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All of the responses so far seem to have missed the requirement that the objects being matched need to be atomic. The following does this:

Cases[testList, {a___?AtomQ} /; Equal[a]]

If you don't define identical in the sense of Equal you could have used:

Cases[testList, {(a_?AtomQ) ...}]

With a slightly modified test list you'll see other methods fail the requirement

testList = {{1, 1.0, 1.0}, {a, b, c}, {Exp[Pi] + 1, Exp[Pi] + 1, Exp[Pi] + 1}, {}, {3}};

they all incorrectly match the 3rd element too.

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Does this work for you?

testList = {
  {1, 1.0, 1.},
  {a, b, c},
  {0, Exp[Pi*I] + 1.0, Sin[Pi]}
}
Cases[testList, _List?(Equal @@ # &)]

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Using Condition, instead of PatternTest:

In[31]:= testList = {{1, 1.0, 1.}, {a, b, c}, {0, Exp[Pi*I] + 1.0, 
    Sin[Pi]}, {}, {3}};

Cases[testList, {a___} /; Equal[a]]

Out[32]= {{1, 1., 1.}, {0, 0., 0}, {}, {3}}

(and expanding on Mark's list of test cases to cover empty and singleton lists.)