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There are three other kinds of irrefutable patterns, two of which we will introduce now (the other we will delay until Section 4.4). ... Lazy patterns are irrefutable: matching a value v against ~pat always succeeds, regardless of pat. Operationally speaking, if an identifier in pat is later "used" on the right-hand-side,
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I hadn’t come across irrefutable patterns (also called lazy patterns) in Haskell before and was of course curious. This is an attempt at illustrating the difference between lazy and non-lazy pattern matching.
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Essentially, when you only have the single constructor for the type, e.g. tuples. Multiple equations won't work nicely with irrefutable patterns. To see this, let's examine what would happen were we to make head have an irrefutable pattern:
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; There is a notion of ``irrefutable patterns'' used by some syntactic constructions. Matching against these patterns never fails. An ``irrefutable pattern'' is either: ... A tuple with irrefutable patterns.
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3.1 Irrefutable Patterns ... Solution: Clean doesn't have any equivalent notation, however we note that Clean does support ``let'' expressions which, in the Haskell'98 report, are defined using irrefutable patterns. ... Where to are all the irrefutable patterns in and to are unique variable names that do not occur free in .
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Wikipatterns.com is a toolbox of patterns & anti-patterns, and a guide to the stages of wiki adoption. It's also a wiki, which means you can help build the information based on your experiences! Beyond this site, there are many other additional resources.
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Just want to mention that this is an issue of pattern matching semantics, not tied to tuples, so any kind of data structure would have the same issue. Lazy pattern matching is available (in the form of irrefutable patterns):
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CiteSeerX - Document Details (Isaac Councill, Lee Giles): . Pattern matching is a great convenience in programming. However, pattern matching has its problems: it conicts with data abstraction; ... it is complex (at least in Haskell, which has pattern guards, irrefutable patterns, n+k patterns, as patterns, etc.);
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Wood Carving, Online design packages that you download into your computer this afternoon and be carving tonight. Includes packet themes as Florals, Mythology, Shell Patterns,Traditional and Wood Spirits. ... Well over 1,500 Patterns & Designs to choose from! Designs Online Since 1997!
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Now, how can I tell (you) how the target > repo differs from the source repo? How can I get rid of all the > other files in the repo that don't matter? I guess this is what the > boiling down step is about.... ... Next message: [darcs-users] [issue701] Irrefutable pattern failed for pattern Data.Maybe.Just a2...
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