BlankNullSequence
 Usage
• ___ (three _ characters) or BlankNullSequence[ ] is a pattern object that can stand for any sequence of zero or more Mathematica expressions.
• ___h or BlankNullSequence[h] can stand for any sequence of expressions, all of which have head h.
Notes
• Blank sequences work slightly differently depending on whether or not the head of the expression in which they appear is a symbol with the attribute Flat. • Consider matching the pattern f[ ,  , ... , ___,  , ... ] against the expression f[ ,  , ... ,  , ... ,  , ... ]. If f is a symbol with attribute Flat, then the ___ will be taken to stand for the expression f[ , ... ]. If f is not a symbol with attribute Flat, then ___ will be taken to stand for the sequence of expressions  , ... . With a named pattern, such as x___, x can be used only as an element in an expression. The sequence of expressions  , ... is "spliced in" to replace x, thereby usually increasing the length of the expression. • If ___ matches a sequence of length more than one, then the sequence will be represented by a Sequence object. In most uses of ___, however, the Sequence object will automatically be spliced into another expression, and will never appear explicitly. • New in Version 1.
|
