This is documentation for Mathematica 6, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.1)

Pattern (:)

s:obj
represents the pattern object obj, assigned the name s.
  • The name s 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.
New in 1