WolframLang: Pattern Syntax

Here's a list of all pattern syntax. [see Pattern Matching]

Literal expression stand by itself. It can also be used in pattern matching. For example: symbol a matches itself, number 3 matches itself, string "abc" matches itself, and arbitrary expression f[a,b,c] matches itself.

_

any Expression

ReplaceAll[ {3,4}, _ -> x ] === x

x_

any expression, given the name x

ReplaceAll[ {3,4}, x_ -> x+y ] === {3 + y, 4 + y}

_h

any expression with Head h

ReplaceAll[ {3, a, 4.5}, _Integer -> n ] === {n, a, 4.5}

ReplaceAll[ {3, a, 4.5}, _List -> n ] === n

ReplaceAll[ {3, f[a], 4.5}, _f -> n ] === {3, n, 4.5}

x_h

any expression with Head h, given the name x

ReplaceAll[ {3, a}, x_List -> f[x] ] === f[{3, a}]

ReplaceAll[ {3, f[a]}, x_f -> g[x] ] === {3, g[f[a]]}

__

any sequence of one or more expressions. (2 LOW LINE characters)

___

any sequence of zero or more expressions (3 LOW LINE characters)

x__ and x___

sequences of expressions, given the name x

__h and ___h

sequences of expressions, each with Head h

x__h and x___h

sequences of expressions with Head h, given the name x

x:pattern

a pattern, given the name x

pattern?test

a pattern that yields True when test is applied to its value

PatternSequence[p1,p2,…]

a sequence of patterns

OrderlessPatternSequence[p1,p2,…]

an orderless sequence of patterns

KeyValuePattern[{‹key1› → ‹val1›,…}]

an orderless sequence of key → val pairs

x_:v

an expression with default value v

x_h:v

an expression with Head h and default value v

x_.

an expression with a globally defined default value

Optional[x_h]

an expression that must have Head h, and has a globally defined default value

Except[c]

any expression except one that matches c

Except[c,pattern]

any expression matching pattern, except one that matches c

pattern..

a pattern repeated one or more times

pattern...

a pattern repeated zero or more times

Repeated[pattern, spec]

a pattern repeated according to spec

pattern1|pattern2|…

a pattern that matches at least one of the patterni

pattern/;cond

a pattern for which cond evaluates to True

HoldPattern[pattern]

a pattern not evaluated

Verbatim[expr]

an expression to be matched verbatim

OptionsPattern[]

a sequence of options

Longest[pattern]

the longest sequence consistent with pattern

Shortest[pattern]

the shortest sequence consistent with pattern

PatternsAndTransformationRules