You can incorporate the pattern from Danny's code without using a Condition like f[x_, syms:{_Symbol ..}] := ... although in this case I would use a BlankSequence rather than Repeated: f[x_, syms:{__Symbol}] := ...

Thanks Neil & Daniel. Those solutions are not really "easy" and not really easy to read, but they work. BTW: I think putting the constraints after the body end is less readable then putting them directly into the "function declaration".

Hence I will write according to Neil:

ClearAll[f, x, a, b];
f[x_, syms_List /; VectorQ[syms, Head[#] == Symbol &]] := 
  Style[x*syms, Red];
{f[2, 3], f[2, a], f[2, {a, 4}], f[2, {a, b}]}

= {f[2,3],f[2,a],f[2,{a,4}],{2 a,2 b}}

or Daniel's proposal, which is a bit shorter but perhaps less readable:

ClearAll[f, x, a, b];
f[x_, syms_List /; MatchQ[syms, {_Symbol ..}]] := Style[x*syms, Red];
{f[2, 3], f[2, a], f[2, {a, 4}], f[2, {a, b}]}

={f[2,3],f[2,a],f[2,{a,4}],{2 a,2 b}}

Extending those constarints to anything else is clear.

Werner,

You can do this:

In[13]:= mi[list_] := yes /; VectorQ[list, IntegerQ]

In[25]:= mi[{1, 2, 3, 4, 5}]

Out[25]= yes

In[15]:= mi[{1, 2, 3, 4, 5, t}]

Out[15]= mi[{1, 2, 3, 4, 5, t}]

In[21]:= 
mi[list_] := yes /; VectorQ[list, IntegerQ[#] || Head[#] == Symbol &]

In[22]:= mi[{1, 2, 3, 4, 5, t}]

Out[22]= yes

In[23]:= 
mi[list_] := yes /; VectorQ[list, IntegerQ[#] || MatchQ[#, _Symbol] &]

In[24]:= mi[{1, 2, 3, 4, 5, t}]

Out[24]= yes

Also works with ArrayQ for 2 dimensions. See some other good examples here and look at putting constraints on patterns.

Regards,

Neil