# "Meta-matching" patterns [duplicate]

The title refers to the general problem of writing patterns to match pattern-containing expressions (hence "meta-match").

Here's an example.

In the following rules

0 -> "A"
foo[1] -> bar[2]
{1, 10} -> 11


the left-hand-sides contain no patterns, at least explicitly. I'll refer to such rules as being "pattern-free".

Now, given a list of rules (rules), how can one obtain the sublist consisting only of the pattern-free ones?

This naive solution won't work:

Cases[rules,x_ /; FreeQ[x, (Blank[___] | BlankSequence[___] | BlankNullSequence[___])]]


I can solve this problem at least with the following hack

Cases[(rules /. (Blank | BlankSequence | BlankNullSequence) -> $patt), y_ /; FreeQ[y,$patt[___]]]


or

Cases[(rules /. x:(Blank | BlankSequence | BlankNullSequence) -> $patt[x]), y_ /; FreeQ[y,$patt[_][___]]
] /. \$patt[z_] -> z


...but I figure that Mathematica may provide standard constructs to deal with such situations. If so, I'd like to learn what they are.

• Verbatim and PatternHold are useful. Jan 16, 2015 at 15:07
• What @Szabolcs said. Except the second one should be HoldPattern. Jan 16, 2015 at 15:44
• Related: (2778), (17591), (17892), (38436), (43972) Jan 16, 2015 at 18:36
• How would you owant to deal with expressions with things like x[Verbatim[2/;True]] or x[HoldPattern[2]]?
– Rojo
Jan 16, 2015 at 20:53