Longest

Longest[p]

is a pattern object that matches the longest sequence consistent with the pattern p.

Details

  • Longest works for both ordinary expression patterns and string patterns.
  • If several Longest objects occur in the same expression, those that appear first are given higher priority to match longest sequences.
  • Longest[p,pri] is given priority pri to be the longest sequence. Matches for longest sequences are tried first for Longest objects with higher priorities.
  • Priorities can be any expression, and are ordered in standard Wolfram Language Sort order. Longest[p] specifies the highest possible priority.
  • Longest objects with equal priorities are tried in the order they appear in the expression.
  • If no explicit Longest or Shortest is given, ordinary expression patterns are normally effectively assumed to be Shortest[p], while string patterns are assumed to be Longest[p].
  • For ordinary expressions, Longest[p] specifies that not just p itself, but also all parts of p should match the longest sequences.
  • Longest[p] corresponds to a "greedy pattern".
  • Longest[p] may not correspond to the absolutely longest expression matching p if there are additional constraints elsewhere in the pattern.

Examples

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Basic Examples  (1)

Control ambiguous matches by using Longest:

Scope  (2)

Longest works with string patterns:

Use priorities to affect ambiguous choices:

Applications  (2)

Find the longest sequence of integers:

Consider the following variable length argument function:

Use Longest to express it as one pattern:

Properties & Relations  (2)

For expressions, when a pattern has consecutive sequences, the last one is effectively wrapped in Longest:

For string patterns, Longest provides "greedy" matches of all maximum-length matches:

Possible Issues  (3)

When there are additional constraints, Longest may not match the absolute longest sequence:

For string patterns, Longest will match all maximal substrings, not just the absolute longest substring:

Priorities are not supported in string expressions:

Introduced in 2007
 (6.0)