• ← PatternTest
• → Repeated

Pattern

Pattern[symb, patt] or symb : patt

assigns the name symb to the pattern patt.

symb_head

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

symb : patt : default

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

• • FullForm[a_b]

• • FullForm[a:_:b]

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

• • x = 2

• • x_

Nested Pattern assign 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[] /. f[a:b_:d] -> {a, b}

FullForm:

• • FullForm[a:b:c:d:e]