Repeated

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

Repeated[p, max]

represents from 1 to max expressions matching p.

Repeated[p, {min, max}]

represents between min and max expressions matching p.

Repeated[p, {n}]

represents exactly n expressions matching p.

Notes

p.. or Repeated\[p\] is a pattern object that represents a sequence of one or more expressions, each matching p.

Examples (5)

Every input below was run against the current Mathilda build and its output recorded.

Applications (5)

In[1]:= MatchQ[{1, 1, 1}, {Repeated[1]}]
Out[1]= True

In[2]:= MatchQ[{1, 1, 2}, {Repeated[1]}]
Out[2]= False

In[3]:= MatchQ[{1, 2, 3}, {_Integer ..}]
Out[3]= True

In[4]:= Cases[{{1}, {1, 1}, {1, 1, 1}, {1, 1, 1, 1}}, {Repeated[1, {2, 3}]}]
Out[4]= {{1, 1}, {1, 1, 1}}

In[5]:= MatchQ[{1, 2, 3, 4}, {Repeated[_Integer, {4}]}]
Out[5]= True

Implementation notes

Repeated[p] (p..) is a pattern object handled entirely inside the matcher, not by a builtin. is_repeated in src/match.c recognises the Repeated head, sets the matched-length range to [1, ∞) by default, and parses an optional count spec: Repeated[p, max] gives [1, max], Repeated[p, {n}] gives exactly n, Repeated[p, {min, max}] gives [min, max] (with Infinity allowed as an open upper bound). The argument-sequence matcher then matches a run of consecutive arguments each satisfying p, using the standard backtracking that explores valid run lengths within the range.

Attributes: none registered.

References

• Source: src/match.c
• Specification: docs/spec/builtins/pattern-matching.md
• Tests: tests/test_match_extensive.c
• Tests: tests/test_parse.c
• Tests: tests/test_replace.c
• Tests: tests/test_stringfns.c

Notes & additional examples

Notes

Repeated[p] (postfix p..) matches a sequence of one or more expressions each satisfying p. The optional second argument bounds the count, e.g. Repeated[p, {2, 4}] for between two and four.