4

I am trying to rewrite patterns. For example, I'd like to rewrite the pattern

jFoo_Integer

which has FullForm

Pattern[jFoo,Blank[Integer]]

into just 

Blank[Integer]

In other words, I want to strip out the names of patterns. I tried the following

jFoo_Integer /. {Pattern[nym_, Blank[typ_]] :> {nym, typ}}

which does not match or reduce and produces the (IMO bogus) error message

Pattern::patvar: First element in pattern Pattern[nym_,Blank[typ_]] is not a valid pattern name. >>

I also tried

    Pattern[jFoo,Blank[Integer]] /. {Pattern[nym_, Blank[typ_]] :> {nym, typ}}
    Pattern[jFoo,Blank[Integer]] /. {Verbatim[Pattern][nym_, Blank[typ_]] :> {nym, typ}}
    jFoo_Integer /. {Verbatim[Pattern][nym_, Blank[typ_]] :> {nym, typ}}
    jFoo_Integer /. {Verbatim[Pattern][nym_, Blank[typ_]] :> {nym, typ}}

all with exactly the same (failed) results.

Any hints, please & thanks?

Reb.Cabin
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2 Answers2

7

What you want is probably

jFoo_Integer /. Verbatim[Pattern][nym_, Verbatim[Blank][typ_]] :> {nym, typ}
(* {jFoo, Integer} *)

The usage of Verbatim points it out

Verbatim[expr] represents expr in pattern matching, requiring that expr be matched exactly as it appears, with no substitutions for blanks or other transformations.

halirutan
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3

I'm not sure how do you want to work with it, but those are ways to go:

List @@ (jFoo_Integer)

{jFoo, _Integer}

(jFoo_Integer) /. x_Pattern :> {x[[1]], x[[2]]}

{jFoo, _Integer}

(jFoo_Integer)[[2]]

_Integer
Kuba
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