• ← OptionsPattern
• → Repeated

Pattern

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Pattern[symb, pat]

symb : pat

assigns the name symb to the pattern pat.

symb_head

is equivalent to symb : _head (accordingly with __ and ___).

symb : pat : default

is a pattern with name symb and default value default, equivalent to Optional[pat : symb, default].

• • FullForm[a_b]

• • FullForm[a:_:b]

Pattern has attribute HoldFirst, so it does not evaluate its name:

• • x = 2

• • x_

Nested Pattern assigns multiple names to the same pattern. Still, the last parameter is the default value.

• • f[y] /. f[a:b,_:d] -> {a, b}

This is equivalent to:

• • f[a] /. f[a:_:b] -> {a, b}

FullForm:

• • FullForm[a:b:c:d:e]

• • f[] /. f[a:_:b] -> {a, b}