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sym:obj or Pattern[sym,obj]

represents the pattern object obj, assigned the name sym.

Details
Details and Options Details and Options
Examples  
Basic Examples  
Scope  
Properties & Relations  
Possible Issues  
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Pattern

sym:obj or Pattern[sym,obj]

represents the pattern object obj, assigned the name sym.

Details

  • The name sym must be a symbol.
  • The object obj can be any pattern object.
  • When a transformation rule is used, any occurrence of s on the right‐hand side is replaced by whatever expression it matched on the left‐hand side.
  • The operator : has a comparatively low precedence. The expression x:_+_ is thus interpreted as x:(_+_), not (x:_)+_.
  • The form s_ is equivalent to s:_. Similarly, s_h is equivalent to s:_h, s__ to s:__, and so on. »

Examples

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Basic Examples  (1)

Give a name to lists of integers:

Wolfram Language code: Cases[{{1, 2, 3}, a, {4, 5}}, t : {__Integer} :> t ^ 2]
Wolfram Language code: Cases[{{1, 2, 3}, a, {4, 5}}, Pattern[t, {__Integer}] :> t ^ 2]

Scope  (1)

Use Pattern in any pattern-matching function including ReplaceAll:

Wolfram Language code: {x} /. n : (x | y) :> n + 2

Cases:

Wolfram Language code: Cases[{x, y, z}, n : (x | y) :> n + 2]

And MatchQ:

Wolfram Language code: MatchQ[x, n : (x | y)]

Properties & Relations  (1)

The forms s_ and s:_ are equivalent:

Wolfram Language code: {FullForm[s_], FullForm[s : _]}

This extends to forms with a specified head:

Wolfram Language code: {FullForm[s_h], FullForm[s : _h]}

As well as forms involving BlankSequence and BlankNullSequence:

Wolfram Language code: {FullForm[s__], FullForm[s : ___]}

Possible Issues  (1)

The input s:v is a form of Pattern only if s is a symbol:

Wolfram Language code: FullForm[s : v]

If s is a special input form for Blank[…] or Pattern[sym,Blank[…]], then s:v is Optional[s,v]:

Wolfram Language code: {FullForm[_ : v], FullForm[s_ : v]}

Forms involving BlankSequence[…] and BlankNullSequence[…] are similar:

Wolfram Language code: {FullForm[__ : v], FullForm[s___ : v]}

If s is any other expression, the form is not valid input:

Wolfram Language code: ToExpression["f[]:v"]
Wolfram Research (1988), Pattern, Wolfram Language function, https://reference.wolfram.com/language/ref/Pattern.html.

Text

Wolfram Research (1988), Pattern, Wolfram Language function, https://reference.wolfram.com/language/ref/Pattern.html.

CMS

Wolfram Language. 1988. "Pattern." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Pattern.html.

APA

Wolfram Language. (1988). Pattern. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Pattern.html

BibTeX

@misc{reference.wolfram_2026_pattern, author="Wolfram Research", title="{Pattern}", year="1988", howpublished="\url{https://reference.wolfram.com/language/ref/Pattern.html}", note=[Accessed: 12-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_pattern, organization={Wolfram Research}, title={Pattern}, year={1988}, url={https://reference.wolfram.com/language/ref/Pattern.html}, note=[Accessed: 12-June-2026]}